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platform_bionic/libc/bionic/pthread.c
Elliott Hughes 1e980b6bc8 Fix the duplication in the debugging code. 
We had two copies of the backtrace code, and two copies of the
libcorkscrew /proc/pid/maps code. This patch gets us down to one.

We also had hacks so we could log in the malloc debugging code.
This patch pulls the non-allocating "printf" code out of the
dynamic linker so everyone can share.

This patch also makes the leak diagnostics easier to read, and
makes it possible to paste them directly into the 'stack' tool (by
using relative PCs).

This patch also fixes the stdio standard stream leak that was
causing a leak warning every time tf_daemon ran.

Bug: 7291287
Change-Id: I66e4083ac2c5606c8d2737cb45c8ac8a32c7cfe8
2013-01-18 22:20:06 -08:00

2257 lines
70 KiB
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/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <malloc.h>
#include <memory.h>
#include <pthread.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/atomics.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include "bionic_atomic_inline.h"
#include "bionic_futex.h"
#include "bionic_pthread.h"
#include "bionic_ssp.h"
#include "bionic_tls.h"
#include "debug_format.h"
#include "pthread_internal.h"
#include "thread_private.h"
extern void pthread_debug_mutex_lock_check(pthread_mutex_t *mutex);
extern void pthread_debug_mutex_unlock_check(pthread_mutex_t *mutex);
extern int __pthread_clone(int (*fn)(void*), void *child_stack, int flags, void *arg);
extern void _exit_with_stack_teardown(void * stackBase, int stackSize, int retCode);
extern void _exit_thread(int retCode);
int __futex_wake_ex(volatile void *ftx, int pshared, int val)
{
return __futex_syscall3(ftx, pshared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, val);
}
int __futex_wait_ex(volatile void *ftx, int pshared, int val, const struct timespec *timeout)
{
return __futex_syscall4(ftx, pshared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, val, timeout);
}
#define __likely(cond) __builtin_expect(!!(cond), 1)
#define __unlikely(cond) __builtin_expect(!!(cond), 0)
#ifdef __i386__
#define ATTRIBUTES __attribute__((noinline)) __attribute__((fastcall))
#else
#define ATTRIBUTES __attribute__((noinline))
#endif
void ATTRIBUTES _thread_created_hook(pid_t thread_id);
static const int kPthreadInitFailed = 1;
#define PTHREAD_ATTR_FLAG_DETACHED 0x00000001
#define PTHREAD_ATTR_FLAG_USER_STACK 0x00000002
#define DEFAULT_STACKSIZE (1024 * 1024)
static pthread_mutex_t mmap_lock = PTHREAD_MUTEX_INITIALIZER;
static const pthread_attr_t gDefaultPthreadAttr = {
.flags = 0,
.stack_base = NULL,
.stack_size = DEFAULT_STACKSIZE,
.guard_size = PAGE_SIZE,
.sched_policy = SCHED_NORMAL,
.sched_priority = 0
};
static pthread_internal_t* gThreadList = NULL;
static pthread_mutex_t gThreadListLock = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t gDebuggerNotificationLock = PTHREAD_MUTEX_INITIALIZER;
static void _pthread_internal_remove_locked(pthread_internal_t* thread) {
if (thread->next != NULL) {
thread->next->prev = thread->prev;
}
if (thread->prev != NULL) {
thread->prev->next = thread->next;
} else {
gThreadList = thread->next;
}
// The main thread is not heap-allocated. See __libc_init_tls for the declaration,
// and __libc_init_common for the point where it's added to the thread list.
if (thread->allocated_on_heap) {
free(thread);
}
}
static void _pthread_internal_remove(pthread_internal_t* thread) {
pthread_mutex_lock(&gThreadListLock);
_pthread_internal_remove_locked(thread);
pthread_mutex_unlock(&gThreadListLock);
}
__LIBC_ABI_PRIVATE__ void _pthread_internal_add(pthread_internal_t* thread) {
pthread_mutex_lock(&gThreadListLock);
// We insert at the head.
thread->next = gThreadList;
thread->prev = NULL;
if (thread->next != NULL) {
thread->next->prev = thread;
}
gThreadList = thread;
pthread_mutex_unlock(&gThreadListLock);
}
__LIBC_ABI_PRIVATE__ pthread_internal_t*
__get_thread(void)
{
void** tls = (void**)__get_tls();
return (pthread_internal_t*) tls[TLS_SLOT_THREAD_ID];
}
void*
__get_stack_base(int *p_stack_size)
{
pthread_internal_t* thread = __get_thread();
*p_stack_size = thread->attr.stack_size;
return thread->attr.stack_base;
}
void __init_tls(void** tls, void* thread) {
((pthread_internal_t*) thread)->tls = tls;
// Zero-initialize all the slots.
for (size_t i = 0; i < BIONIC_TLS_SLOTS; ++i) {
tls[i] = NULL;
}
// Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0.
tls[TLS_SLOT_SELF] = (void*) tls;
tls[TLS_SLOT_THREAD_ID] = thread;
// Stack guard generation may make system calls, and those system calls may fail.
// If they do, they'll try to set errno, so we can only do this after calling __set_tls.
__set_tls((void*) tls);
tls[TLS_SLOT_STACK_GUARD] = __generate_stack_chk_guard();
}
/*
* This trampoline is called from the assembly _pthread_clone() function.
*/
void __thread_entry(int (*func)(void*), void *arg, void **tls)
{
// Wait for our creating thread to release us. This lets it have time to
// notify gdb about this thread before we start doing anything.
//
// This also provides the memory barrier needed to ensure that all memory
// accesses previously made by the creating thread are visible to us.
pthread_mutex_t* start_mutex = (pthread_mutex_t*) &tls[TLS_SLOT_SELF];
pthread_mutex_lock(start_mutex);
pthread_mutex_destroy(start_mutex);
pthread_internal_t* thread = (pthread_internal_t*) tls[TLS_SLOT_THREAD_ID];
__init_tls(tls, thread);
if ((thread->internal_flags & kPthreadInitFailed) != 0) {
pthread_exit(NULL);
}
int result = func(arg);
pthread_exit((void*) result);
}
#include <private/logd.h>
__LIBC_ABI_PRIVATE__
int _init_thread(pthread_internal_t* thread, pid_t kernel_id, const pthread_attr_t* attr,
void* stack_base, bool add_to_thread_list)
{
int error = 0;
thread->attr = *attr;
thread->attr.stack_base = stack_base;
thread->kernel_id = kernel_id;
// Make a note of whether the user supplied this stack (so we know whether or not to free it).
if (attr->stack_base == stack_base) {
thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_STACK;
}
// Set the scheduling policy/priority of the thread.
if (thread->attr.sched_policy != SCHED_NORMAL) {
struct sched_param param;
param.sched_priority = thread->attr.sched_priority;
if (sched_setscheduler(kernel_id, thread->attr.sched_policy, &param) == -1) {
// For backwards compatibility reasons, we just warn about failures here.
// error = errno;
const char* msg = "pthread_create sched_setscheduler call failed: %s\n";
__libc_format_log(ANDROID_LOG_WARN, "libc", msg, strerror(errno));
}
}
pthread_cond_init(&thread->join_cond, NULL);
thread->join_count = 0;
thread->cleanup_stack = NULL;
if (add_to_thread_list) {
_pthread_internal_add(thread);
}
return error;
}
static void *mkstack(size_t size, size_t guard_size)
{
pthread_mutex_lock(&mmap_lock);
int prot = PROT_READ | PROT_WRITE;
int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
void* stack = mmap(NULL, size, prot, flags, -1, 0);
if (stack == MAP_FAILED) {
stack = NULL;
goto done;
}
if (mprotect(stack, guard_size, PROT_NONE) == -1) {
munmap(stack, size);
stack = NULL;
goto done;
}
done:
pthread_mutex_unlock(&mmap_lock);
return stack;
}
/*
* Create a new thread. The thread's stack is laid out like so:
*
* +---------------------------+
* | pthread_internal_t |
* +---------------------------+
* | |
* | TLS area |
* | |
* +---------------------------+
* | |
* . .
* . stack area .
* . .
* | |
* +---------------------------+
* | guard page |
* +---------------------------+
*
* note that TLS[0] must be a pointer to itself, this is required
* by the thread-local storage implementation of the x86 Linux
* kernel, where the TLS pointer is read by reading fs:[0]
*/
int pthread_create(pthread_t *thread_out, pthread_attr_t const * attr,
void *(*start_routine)(void *), void * arg)
{
int old_errno = errno;
/* this will inform the rest of the C library that at least one thread
* was created. this will enforce certain functions to acquire/release
* locks (e.g. atexit()) to protect shared global structures.
*
* this works because pthread_create() is not called by the C library
* initialization routine that sets up the main thread's data structures.
*/
__isthreaded = 1;
pthread_internal_t* thread = calloc(sizeof(*thread), 1);
if (thread == NULL) {
return ENOMEM;
}
thread->allocated_on_heap = true;
if (attr == NULL) {
attr = &gDefaultPthreadAttr;
}
// make sure the stack is PAGE_SIZE aligned
size_t stack_size = (attr->stack_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);
uint8_t* stack = attr->stack_base;
if (stack == NULL) {
stack = mkstack(stack_size, attr->guard_size);
if (stack == NULL) {
free(thread);
return ENOMEM;
}
}
// Make room for TLS
void** tls = (void**)(stack + stack_size - BIONIC_TLS_SLOTS*sizeof(void*));
// Create a mutex for the thread in TLS_SLOT_SELF to wait on once it starts so we can keep
// it from doing anything until after we notify the debugger about it
//
// This also provides the memory barrier we need to ensure that all
// memory accesses previously performed by this thread are visible to
// the new thread.
pthread_mutex_t* start_mutex = (pthread_mutex_t*) &tls[TLS_SLOT_SELF];
pthread_mutex_init(start_mutex, NULL);
pthread_mutex_lock(start_mutex);
tls[TLS_SLOT_THREAD_ID] = thread;
int flags = CLONE_FILES | CLONE_FS | CLONE_VM | CLONE_SIGHAND |
CLONE_THREAD | CLONE_SYSVSEM | CLONE_DETACHED;
int tid = __pthread_clone((int(*)(void*))start_routine, tls, flags, arg);
if (tid < 0) {
int clone_errno = errno;
pthread_mutex_unlock(start_mutex);
if (stack != attr->stack_base) {
munmap(stack, stack_size);
}
free(thread);
errno = old_errno;
return clone_errno;
}
int init_errno = _init_thread(thread, tid, attr, stack, true);
if (init_errno != 0) {
// Mark the thread detached and let its __thread_entry run to
// completion. (It'll just exit immediately, cleaning up its resources.)
thread->internal_flags |= kPthreadInitFailed;
thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED;
pthread_mutex_unlock(start_mutex);
errno = old_errno;
return init_errno;
}
// Notify any debuggers about the new thread.
pthread_mutex_lock(&gDebuggerNotificationLock);
_thread_created_hook(tid);
pthread_mutex_unlock(&gDebuggerNotificationLock);
// Publish the pthread_t and let the thread run.
*thread_out = (pthread_t) thread;
pthread_mutex_unlock(start_mutex);
return 0;
}
int pthread_attr_init(pthread_attr_t * attr)
{
*attr = gDefaultPthreadAttr;
return 0;
}
int pthread_attr_destroy(pthread_attr_t * attr)
{
memset(attr, 0x42, sizeof(pthread_attr_t));
return 0;
}
int pthread_attr_setdetachstate(pthread_attr_t * attr, int state)
{
if (state == PTHREAD_CREATE_DETACHED) {
attr->flags |= PTHREAD_ATTR_FLAG_DETACHED;
} else if (state == PTHREAD_CREATE_JOINABLE) {
attr->flags &= ~PTHREAD_ATTR_FLAG_DETACHED;
} else {
return EINVAL;
}
return 0;
}
int pthread_attr_getdetachstate(pthread_attr_t const * attr, int * state)
{
*state = (attr->flags & PTHREAD_ATTR_FLAG_DETACHED)
? PTHREAD_CREATE_DETACHED
: PTHREAD_CREATE_JOINABLE;
return 0;
}
int pthread_attr_setschedpolicy(pthread_attr_t * attr, int policy)
{
attr->sched_policy = policy;
return 0;
}
int pthread_attr_getschedpolicy(pthread_attr_t const * attr, int * policy)
{
*policy = attr->sched_policy;
return 0;
}
int pthread_attr_setschedparam(pthread_attr_t * attr, struct sched_param const * param)
{
attr->sched_priority = param->sched_priority;
return 0;
}
int pthread_attr_getschedparam(pthread_attr_t const * attr, struct sched_param * param)
{
param->sched_priority = attr->sched_priority;
return 0;
}
int pthread_attr_setstacksize(pthread_attr_t * attr, size_t stack_size)
{
if ((stack_size & (PAGE_SIZE - 1) || stack_size < PTHREAD_STACK_MIN)) {
return EINVAL;
}
attr->stack_size = stack_size;
return 0;
}
int pthread_attr_getstacksize(pthread_attr_t const * attr, size_t * stack_size)
{
*stack_size = attr->stack_size;
return 0;
}
int pthread_attr_setstackaddr(pthread_attr_t * attr __attribute__((unused)),
void * stack_addr __attribute__((unused)))
{
// This was removed from POSIX.1-2008, and is not implemented on bionic.
// Needed for ABI compatibility with the NDK.
return ENOSYS;
}
int pthread_attr_getstackaddr(pthread_attr_t const * attr, void ** stack_addr)
{
// This was removed from POSIX.1-2008.
// Needed for ABI compatibility with the NDK.
*stack_addr = (char*)attr->stack_base + attr->stack_size;
return 0;
}
int pthread_attr_setstack(pthread_attr_t * attr, void * stack_base, size_t stack_size)
{
if ((stack_size & (PAGE_SIZE - 1) || stack_size < PTHREAD_STACK_MIN)) {
return EINVAL;
}
if ((uint32_t)stack_base & (PAGE_SIZE - 1)) {
return EINVAL;
}
attr->stack_base = stack_base;
attr->stack_size = stack_size;
return 0;
}
int pthread_attr_getstack(pthread_attr_t const * attr, void ** stack_base, size_t * stack_size)
{
*stack_base = attr->stack_base;
*stack_size = attr->stack_size;
return 0;
}
int pthread_attr_setguardsize(pthread_attr_t * attr, size_t guard_size)
{
if (guard_size & (PAGE_SIZE - 1) || guard_size < PAGE_SIZE) {
return EINVAL;
}
attr->guard_size = guard_size;
return 0;
}
int pthread_attr_getguardsize(pthread_attr_t const * attr, size_t * guard_size)
{
*guard_size = attr->guard_size;
return 0;
}
int pthread_getattr_np(pthread_t thid, pthread_attr_t * attr)
{
pthread_internal_t * thread = (pthread_internal_t *)thid;
*attr = thread->attr;
return 0;
}
int pthread_attr_setscope(pthread_attr_t *attr __attribute__((unused)), int scope)
{
if (scope == PTHREAD_SCOPE_SYSTEM)
return 0;
if (scope == PTHREAD_SCOPE_PROCESS)
return ENOTSUP;
return EINVAL;
}
int pthread_attr_getscope(pthread_attr_t const *attr __attribute__((unused)))
{
return PTHREAD_SCOPE_SYSTEM;
}
/* CAVEAT: our implementation of pthread_cleanup_push/pop doesn't support C++ exceptions
* and thread cancelation
*/
void __pthread_cleanup_push( __pthread_cleanup_t* c,
__pthread_cleanup_func_t routine,
void* arg )
{
pthread_internal_t* thread = __get_thread();
c->__cleanup_routine = routine;
c->__cleanup_arg = arg;
c->__cleanup_prev = thread->cleanup_stack;
thread->cleanup_stack = c;
}
void __pthread_cleanup_pop( __pthread_cleanup_t* c, int execute )
{
pthread_internal_t* thread = __get_thread();
thread->cleanup_stack = c->__cleanup_prev;
if (execute)
c->__cleanup_routine(c->__cleanup_arg);
}
/* used by pthread_exit() to clean all TLS keys of the current thread */
static void pthread_key_clean_all(void);
void pthread_exit(void * retval)
{
pthread_internal_t* thread = __get_thread();
void* stack_base = thread->attr.stack_base;
int stack_size = thread->attr.stack_size;
int user_stack = (thread->attr.flags & PTHREAD_ATTR_FLAG_USER_STACK) != 0;
sigset_t mask;
// call the cleanup handlers first
while (thread->cleanup_stack) {
__pthread_cleanup_t* c = thread->cleanup_stack;
thread->cleanup_stack = c->__cleanup_prev;
c->__cleanup_routine(c->__cleanup_arg);
}
// call the TLS destructors, it is important to do that before removing this
// thread from the global list. this will ensure that if someone else deletes
// a TLS key, the corresponding value will be set to NULL in this thread's TLS
// space (see pthread_key_delete)
pthread_key_clean_all();
// if the thread is detached, destroy the pthread_internal_t
// otherwise, keep it in memory and signal any joiners.
if (thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) {
_pthread_internal_remove(thread);
} else {
pthread_mutex_lock(&gThreadListLock);
/* make sure that the thread struct doesn't have stale pointers to a stack that
* will be unmapped after the exit call below.
*/
if (!user_stack) {
thread->attr.stack_base = NULL;
thread->attr.stack_size = 0;
thread->tls = NULL;
}
/* the join_count field is used to store the number of threads waiting for
* the termination of this thread with pthread_join(),
*
* if it is positive we need to signal the waiters, and we do not touch
* the count (it will be decremented by the waiters, the last one will
* also remove/free the thread structure
*
* if it is zero, we set the count value to -1 to indicate that the
* thread is in 'zombie' state: it has stopped executing, and its stack
* is gone (as well as its TLS area). when another thread calls pthread_join()
* on it, it will immediately free the thread and return.
*/
thread->return_value = retval;
if (thread->join_count > 0) {
pthread_cond_broadcast(&thread->join_cond);
} else {
thread->join_count = -1; /* zombie thread */
}
pthread_mutex_unlock(&gThreadListLock);
}
sigfillset(&mask);
sigdelset(&mask, SIGSEGV);
(void)sigprocmask(SIG_SETMASK, &mask, (sigset_t *)NULL);
// destroy the thread stack
if (user_stack)
_exit_thread((int)retval);
else
_exit_with_stack_teardown(stack_base, stack_size, (int)retval);
}
int pthread_join(pthread_t thid, void ** ret_val)
{
pthread_internal_t* thread = (pthread_internal_t*)thid;
if (thid == pthread_self()) {
return EDEADLK;
}
// check that the thread still exists and is not detached
pthread_mutex_lock(&gThreadListLock);
for (thread = gThreadList; thread != NULL; thread = thread->next) {
if (thread == (pthread_internal_t*)thid) {
goto FoundIt;
}
}
pthread_mutex_unlock(&gThreadListLock);
return ESRCH;
FoundIt:
if (thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) {
pthread_mutex_unlock(&gThreadListLock);
return EINVAL;
}
/* wait for thread death when needed
*
* if the 'join_count' is negative, this is a 'zombie' thread that
* is already dead and without stack/TLS
*
* otherwise, we need to increment 'join-count' and wait to be signaled
*/
int count = thread->join_count;
if (count >= 0) {
thread->join_count += 1;
pthread_cond_wait( &thread->join_cond, &gThreadListLock );
count = --thread->join_count;
}
if (ret_val) {
*ret_val = thread->return_value;
}
/* remove thread descriptor when we're the last joiner or when the
* thread was already a zombie.
*/
if (count <= 0) {
_pthread_internal_remove_locked(thread);
}
pthread_mutex_unlock(&gThreadListLock);
return 0;
}
int pthread_detach( pthread_t thid )
{
pthread_internal_t* thread;
int result = 0;
pthread_mutex_lock(&gThreadListLock);
for (thread = gThreadList; thread != NULL; thread = thread->next) {
if (thread == (pthread_internal_t*)thid) {
goto FoundIt;
}
}
result = ESRCH;
goto Exit;
FoundIt:
if (thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) {
result = EINVAL; // Already detached.
goto Exit;
}
if (thread->join_count > 0) {
result = 0; // Already being joined; silently do nothing, like glibc.
goto Exit;
}
thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED;
Exit:
pthread_mutex_unlock(&gThreadListLock);
return result;
}
pthread_t pthread_self(void)
{
return (pthread_t)__get_thread();
}
int pthread_equal(pthread_t one, pthread_t two)
{
return (one == two ? 1 : 0);
}
int pthread_getschedparam(pthread_t thid, int * policy,
struct sched_param * param)
{
int old_errno = errno;
pthread_internal_t * thread = (pthread_internal_t *)thid;
int err = sched_getparam(thread->kernel_id, param);
if (!err) {
*policy = sched_getscheduler(thread->kernel_id);
} else {
err = errno;
errno = old_errno;
}
return err;
}
int pthread_setschedparam(pthread_t thid, int policy,
struct sched_param const * param)
{
pthread_internal_t * thread = (pthread_internal_t *)thid;
int old_errno = errno;
int ret;
ret = sched_setscheduler(thread->kernel_id, policy, param);
if (ret < 0) {
ret = errno;
errno = old_errno;
}
return ret;
}
/* a mutex is implemented as a 32-bit integer holding the following fields
*
* bits: name description
* 31-16 tid owner thread's kernel id (recursive and errorcheck only)
* 15-14 type mutex type
* 13 shared process-shared flag
* 12-2 counter counter of recursive mutexes
* 1-0 state lock state (0, 1 or 2)
*/
/* Convenience macro, creates a mask of 'bits' bits that starts from
* the 'shift'-th least significant bit in a 32-bit word.
*
* Examples: FIELD_MASK(0,4) -> 0xf
* FIELD_MASK(16,9) -> 0x1ff0000
*/
#define FIELD_MASK(shift,bits) (((1 << (bits))-1) << (shift))
/* This one is used to create a bit pattern from a given field value */
#define FIELD_TO_BITS(val,shift,bits) (((val) & ((1 << (bits))-1)) << (shift))
/* And this one does the opposite, i.e. extract a field's value from a bit pattern */
#define FIELD_FROM_BITS(val,shift,bits) (((val) >> (shift)) & ((1 << (bits))-1))
/* Mutex state:
*
* 0 for unlocked
* 1 for locked, no waiters
* 2 for locked, maybe waiters
*/
#define MUTEX_STATE_SHIFT 0
#define MUTEX_STATE_LEN 2
#define MUTEX_STATE_MASK FIELD_MASK(MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_FROM_BITS(v) FIELD_FROM_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_TO_BITS(v) FIELD_TO_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_UNLOCKED 0 /* must be 0 to match __PTHREAD_MUTEX_INIT_VALUE */
#define MUTEX_STATE_LOCKED_UNCONTENDED 1 /* must be 1 due to atomic dec in unlock operation */
#define MUTEX_STATE_LOCKED_CONTENDED 2 /* must be 1 + LOCKED_UNCONTENDED due to atomic dec */
#define MUTEX_STATE_FROM_BITS(v) FIELD_FROM_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_TO_BITS(v) FIELD_TO_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_BITS_UNLOCKED MUTEX_STATE_TO_BITS(MUTEX_STATE_UNLOCKED)
#define MUTEX_STATE_BITS_LOCKED_UNCONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_UNCONTENDED)
#define MUTEX_STATE_BITS_LOCKED_CONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_CONTENDED)
/* return true iff the mutex if locked with no waiters */
#define MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_UNCONTENDED)
/* return true iff the mutex if locked with maybe waiters */
#define MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_CONTENDED)
/* used to flip from LOCKED_UNCONTENDED to LOCKED_CONTENDED */
#define MUTEX_STATE_BITS_FLIP_CONTENTION(v) ((v) ^ (MUTEX_STATE_BITS_LOCKED_CONTENDED ^ MUTEX_STATE_BITS_LOCKED_UNCONTENDED))
/* Mutex counter:
*
* We need to check for overflow before incrementing, and we also need to
* detect when the counter is 0
*/
#define MUTEX_COUNTER_SHIFT 2
#define MUTEX_COUNTER_LEN 11
#define MUTEX_COUNTER_MASK FIELD_MASK(MUTEX_COUNTER_SHIFT, MUTEX_COUNTER_LEN)
#define MUTEX_COUNTER_BITS_WILL_OVERFLOW(v) (((v) & MUTEX_COUNTER_MASK) == MUTEX_COUNTER_MASK)
#define MUTEX_COUNTER_BITS_IS_ZERO(v) (((v) & MUTEX_COUNTER_MASK) == 0)
/* Used to increment the counter directly after overflow has been checked */
#define MUTEX_COUNTER_BITS_ONE FIELD_TO_BITS(1,MUTEX_COUNTER_SHIFT,MUTEX_COUNTER_LEN)
/* Returns true iff the counter is 0 */
#define MUTEX_COUNTER_BITS_ARE_ZERO(v) (((v) & MUTEX_COUNTER_MASK) == 0)
/* Mutex shared bit flag
*
* This flag is set to indicate that the mutex is shared among processes.
* This changes the futex opcode we use for futex wait/wake operations
* (non-shared operations are much faster).
*/
#define MUTEX_SHARED_SHIFT 13
#define MUTEX_SHARED_MASK FIELD_MASK(MUTEX_SHARED_SHIFT,1)
/* Mutex type:
*
* We support normal, recursive and errorcheck mutexes.
*
* The constants defined here *cannot* be changed because they must match
* the C library ABI which defines the following initialization values in
* <pthread.h>:
*
* __PTHREAD_MUTEX_INIT_VALUE
* __PTHREAD_RECURSIVE_MUTEX_VALUE
* __PTHREAD_ERRORCHECK_MUTEX_INIT_VALUE
*/
#define MUTEX_TYPE_SHIFT 14
#define MUTEX_TYPE_LEN 2
#define MUTEX_TYPE_MASK FIELD_MASK(MUTEX_TYPE_SHIFT,MUTEX_TYPE_LEN)
#define MUTEX_TYPE_NORMAL 0 /* Must be 0 to match __PTHREAD_MUTEX_INIT_VALUE */
#define MUTEX_TYPE_RECURSIVE 1
#define MUTEX_TYPE_ERRORCHECK 2
#define MUTEX_TYPE_TO_BITS(t) FIELD_TO_BITS(t, MUTEX_TYPE_SHIFT, MUTEX_TYPE_LEN)
#define MUTEX_TYPE_BITS_NORMAL MUTEX_TYPE_TO_BITS(MUTEX_TYPE_NORMAL)
#define MUTEX_TYPE_BITS_RECURSIVE MUTEX_TYPE_TO_BITS(MUTEX_TYPE_RECURSIVE)
#define MUTEX_TYPE_BITS_ERRORCHECK MUTEX_TYPE_TO_BITS(MUTEX_TYPE_ERRORCHECK)
/* Mutex owner field:
*
* This is only used for recursive and errorcheck mutexes. It holds the
* kernel TID of the owning thread. Note that this works because the Linux
* kernel _only_ uses 16-bit values for thread ids.
*
* More specifically, it will wrap to 10000 when it reaches over 32768 for
* application processes. You can check this by running the following inside
* an adb shell session:
*
OLDPID=$$;
while true; do
NEWPID=$(sh -c 'echo $$')
if [ "$NEWPID" -gt 32768 ]; then
echo "AARGH: new PID $NEWPID is too high!"
exit 1
fi
if [ "$NEWPID" -lt "$OLDPID" ]; then
echo "****** Wrapping from PID $OLDPID to $NEWPID. *******"
else
echo -n "$NEWPID!"
fi
OLDPID=$NEWPID
done
* Note that you can run the same example on a desktop Linux system,
* the wrapping will also happen at 32768, but will go back to 300 instead.
*/
#define MUTEX_OWNER_SHIFT 16
#define MUTEX_OWNER_LEN 16
#define MUTEX_OWNER_FROM_BITS(v) FIELD_FROM_BITS(v,MUTEX_OWNER_SHIFT,MUTEX_OWNER_LEN)
#define MUTEX_OWNER_TO_BITS(v) FIELD_TO_BITS(v,MUTEX_OWNER_SHIFT,MUTEX_OWNER_LEN)
/* Convenience macros.
*
* These are used to form or modify the bit pattern of a given mutex value
*/
/* a mutex attribute holds the following fields
*
* bits: name description
* 0-3 type type of mutex
* 4 shared process-shared flag
*/
#define MUTEXATTR_TYPE_MASK 0x000f
#define MUTEXATTR_SHARED_MASK 0x0010
int pthread_mutexattr_init(pthread_mutexattr_t *attr)
{
if (attr) {
*attr = PTHREAD_MUTEX_DEFAULT;
return 0;
} else {
return EINVAL;
}
}
int pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
{
if (attr) {
*attr = -1;
return 0;
} else {
return EINVAL;
}
}
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type)
{
if (attr) {
int atype = (*attr & MUTEXATTR_TYPE_MASK);
if (atype >= PTHREAD_MUTEX_NORMAL &&
atype <= PTHREAD_MUTEX_ERRORCHECK) {
*type = atype;
return 0;
}
}
return EINVAL;
}
int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)
{
if (attr && type >= PTHREAD_MUTEX_NORMAL &&
type <= PTHREAD_MUTEX_ERRORCHECK ) {
*attr = (*attr & ~MUTEXATTR_TYPE_MASK) | type;
return 0;
}
return EINVAL;
}
/* process-shared mutexes are not supported at the moment */
int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared)
{
if (!attr)
return EINVAL;
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
*attr &= ~MUTEXATTR_SHARED_MASK;
return 0;
case PTHREAD_PROCESS_SHARED:
/* our current implementation of pthread actually supports shared
* mutexes but won't cleanup if a process dies with the mutex held.
* Nevertheless, it's better than nothing. Shared mutexes are used
* by surfaceflinger and audioflinger.
*/
*attr |= MUTEXATTR_SHARED_MASK;
return 0;
}
return EINVAL;
}
int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr, int *pshared)
{
if (!attr || !pshared)
return EINVAL;
*pshared = (*attr & MUTEXATTR_SHARED_MASK) ? PTHREAD_PROCESS_SHARED
: PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_mutex_init(pthread_mutex_t *mutex,
const pthread_mutexattr_t *attr)
{
int value = 0;
if (mutex == NULL)
return EINVAL;
if (__likely(attr == NULL)) {
mutex->value = MUTEX_TYPE_BITS_NORMAL;
return 0;
}
if ((*attr & MUTEXATTR_SHARED_MASK) != 0)
value |= MUTEX_SHARED_MASK;
switch (*attr & MUTEXATTR_TYPE_MASK) {
case PTHREAD_MUTEX_NORMAL:
value |= MUTEX_TYPE_BITS_NORMAL;
break;
case PTHREAD_MUTEX_RECURSIVE:
value |= MUTEX_TYPE_BITS_RECURSIVE;
break;
case PTHREAD_MUTEX_ERRORCHECK:
value |= MUTEX_TYPE_BITS_ERRORCHECK;
break;
default:
return EINVAL;
}
mutex->value = value;
return 0;
}
/*
* Lock a non-recursive mutex.
*
* As noted above, there are three states:
* 0 (unlocked, no contention)
* 1 (locked, no contention)
* 2 (locked, contention)
*
* Non-recursive mutexes don't use the thread-id or counter fields, and the
* "type" value is zero, so the only bits that will be set are the ones in
* the lock state field.
*/
static __inline__ void
_normal_lock(pthread_mutex_t* mutex, int shared)
{
/* convenience shortcuts */
const int unlocked = shared | MUTEX_STATE_BITS_UNLOCKED;
const int locked_uncontended = shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
/*
* The common case is an unlocked mutex, so we begin by trying to
* change the lock's state from 0 (UNLOCKED) to 1 (LOCKED).
* __bionic_cmpxchg() returns 0 if it made the swap successfully.
* If the result is nonzero, this lock is already held by another thread.
*/
if (__bionic_cmpxchg(unlocked, locked_uncontended, &mutex->value) != 0) {
const int locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED;
/*
* We want to go to sleep until the mutex is available, which
* requires promoting it to state 2 (CONTENDED). We need to
* swap in the new state value and then wait until somebody wakes us up.
*
* __bionic_swap() returns the previous value. We swap 2 in and
* see if we got zero back; if so, we have acquired the lock. If
* not, another thread still holds the lock and we wait again.
*
* The second argument to the __futex_wait() call is compared
* against the current value. If it doesn't match, __futex_wait()
* returns immediately (otherwise, it sleeps for a time specified
* by the third argument; 0 means sleep forever). This ensures
* that the mutex is in state 2 when we go to sleep on it, which
* guarantees a wake-up call.
*/
while (__bionic_swap(locked_contended, &mutex->value) != unlocked)
__futex_wait_ex(&mutex->value, shared, locked_contended, 0);
}
ANDROID_MEMBAR_FULL();
}
/*
* Release a non-recursive mutex. The caller is responsible for determining
* that we are in fact the owner of this lock.
*/
static __inline__ void
_normal_unlock(pthread_mutex_t* mutex, int shared)
{
ANDROID_MEMBAR_FULL();
/*
* The mutex state will be 1 or (rarely) 2. We use an atomic decrement
* to release the lock. __bionic_atomic_dec() returns the previous value;
* if it wasn't 1 we have to do some additional work.
*/
if (__bionic_atomic_dec(&mutex->value) != (shared|MUTEX_STATE_BITS_LOCKED_UNCONTENDED)) {
/*
* Start by releasing the lock. The decrement changed it from
* "contended lock" to "uncontended lock", which means we still
* hold it, and anybody who tries to sneak in will push it back
* to state 2.
*
* Once we set it to zero the lock is up for grabs. We follow
* this with a __futex_wake() to ensure that one of the waiting
* threads has a chance to grab it.
*
* This doesn't cause a race with the swap/wait pair in
* _normal_lock(), because the __futex_wait() call there will
* return immediately if the mutex value isn't 2.
*/
mutex->value = shared;
/*
* Wake up one waiting thread. We don't know which thread will be
* woken or when it'll start executing -- futexes make no guarantees
* here. There may not even be a thread waiting.
*
* The newly-woken thread will replace the 0 we just set above
* with 2, which means that when it eventually releases the mutex
* it will also call FUTEX_WAKE. This results in one extra wake
* call whenever a lock is contended, but lets us avoid forgetting
* anyone without requiring us to track the number of sleepers.
*
* It's possible for another thread to sneak in and grab the lock
* between the zero assignment above and the wake call below. If
* the new thread is "slow" and holds the lock for a while, we'll
* wake up a sleeper, which will swap in a 2 and then go back to
* sleep since the lock is still held. If the new thread is "fast",
* running to completion before we call wake, the thread we
* eventually wake will find an unlocked mutex and will execute.
* Either way we have correct behavior and nobody is orphaned on
* the wait queue.
*/
__futex_wake_ex(&mutex->value, shared, 1);
}
}
/* This common inlined function is used to increment the counter of an
* errorcheck or recursive mutex.
*
* For errorcheck mutexes, it will return EDEADLK
* If the counter overflows, it will return EAGAIN
* Otherwise, it atomically increments the counter and returns 0
* after providing an acquire barrier.
*
* mtype is the current mutex type
* mvalue is the current mutex value (already loaded)
* mutex pointers to the mutex.
*/
static __inline__ __attribute__((always_inline)) int
_recursive_increment(pthread_mutex_t* mutex, int mvalue, int mtype)
{
if (mtype == MUTEX_TYPE_BITS_ERRORCHECK) {
/* trying to re-lock a mutex we already acquired */
return EDEADLK;
}
/* Detect recursive lock overflow and return EAGAIN.
* This is safe because only the owner thread can modify the
* counter bits in the mutex value.
*/
if (MUTEX_COUNTER_BITS_WILL_OVERFLOW(mvalue)) {
return EAGAIN;
}
/* We own the mutex, but other threads are able to change
* the lower bits (e.g. promoting it to "contended"), so we
* need to use an atomic cmpxchg loop to update the counter.
*/
for (;;) {
/* increment counter, overflow was already checked */
int newval = mvalue + MUTEX_COUNTER_BITS_ONE;
if (__likely(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) {
/* mutex is still locked, not need for a memory barrier */
return 0;
}
/* the value was changed, this happens when another thread changes
* the lower state bits from 1 to 2 to indicate contention. This
* cannot change the counter, so simply reload and try again.
*/
mvalue = mutex->value;
}
}
__LIBC_HIDDEN__
int pthread_mutex_lock_impl(pthread_mutex_t *mutex)
{
int mvalue, mtype, tid, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
mvalue = mutex->value;
mtype = (mvalue & MUTEX_TYPE_MASK);
shared = (mvalue & MUTEX_SHARED_MASK);
/* Handle normal case first */
if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) ) {
_normal_lock(mutex, shared);
return 0;
}
/* Do we already own this recursive or error-check mutex ? */
tid = __get_thread()->kernel_id;
if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
return _recursive_increment(mutex, mvalue, mtype);
/* Add in shared state to avoid extra 'or' operations below */
mtype |= shared;
/* First, if the mutex is unlocked, try to quickly acquire it.
* In the optimistic case where this works, set the state to 1 to
* indicate locked with no contention */
if (mvalue == mtype) {
int newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
if (__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0) {
ANDROID_MEMBAR_FULL();
return 0;
}
/* argh, the value changed, reload before entering the loop */
mvalue = mutex->value;
}
for (;;) {
int newval;
/* if the mutex is unlocked, its value should be 'mtype' and
* we try to acquire it by setting its owner and state atomically.
* NOTE: We put the state to 2 since we _know_ there is contention
* when we are in this loop. This ensures all waiters will be
* unlocked.
*/
if (mvalue == mtype) {
newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_CONTENDED;
/* TODO: Change this to __bionic_cmpxchg_acquire when we
* implement it to get rid of the explicit memory
* barrier below.
*/
if (__unlikely(__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0)) {
mvalue = mutex->value;
continue;
}
ANDROID_MEMBAR_FULL();
return 0;
}
/* the mutex is already locked by another thread, if its state is 1
* we will change it to 2 to indicate contention. */
if (MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(mvalue)) {
newval = MUTEX_STATE_BITS_FLIP_CONTENTION(mvalue); /* locked state 1 => state 2 */
if (__unlikely(__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0)) {
mvalue = mutex->value;
continue;
}
mvalue = newval;
}
/* wait until the mutex is unlocked */
__futex_wait_ex(&mutex->value, shared, mvalue, NULL);
mvalue = mutex->value;
}
/* NOTREACHED */
}
int pthread_mutex_lock(pthread_mutex_t *mutex)
{
int err = pthread_mutex_lock_impl(mutex);
#ifdef PTHREAD_DEBUG
if (PTHREAD_DEBUG_ENABLED) {
if (!err) {
pthread_debug_mutex_lock_check(mutex);
}
}
#endif
return err;
}
__LIBC_HIDDEN__
int pthread_mutex_unlock_impl(pthread_mutex_t *mutex)
{
int mvalue, mtype, tid, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
mvalue = mutex->value;
mtype = (mvalue & MUTEX_TYPE_MASK);
shared = (mvalue & MUTEX_SHARED_MASK);
/* Handle common case first */
if (__likely(mtype == MUTEX_TYPE_BITS_NORMAL)) {
_normal_unlock(mutex, shared);
return 0;
}
/* Do we already own this recursive or error-check mutex ? */
tid = __get_thread()->kernel_id;
if ( tid != MUTEX_OWNER_FROM_BITS(mvalue) )
return EPERM;
/* If the counter is > 0, we can simply decrement it atomically.
* Since other threads can mutate the lower state bits (and only the
* lower state bits), use a cmpxchg to do it.
*/
if (!MUTEX_COUNTER_BITS_IS_ZERO(mvalue)) {
for (;;) {
int newval = mvalue - MUTEX_COUNTER_BITS_ONE;
if (__likely(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) {
/* success: we still own the mutex, so no memory barrier */
return 0;
}
/* the value changed, so reload and loop */
mvalue = mutex->value;
}
}
/* the counter is 0, so we're going to unlock the mutex by resetting
* its value to 'unlocked'. We need to perform a swap in order
* to read the current state, which will be 2 if there are waiters
* to awake.
*
* TODO: Change this to __bionic_swap_release when we implement it
* to get rid of the explicit memory barrier below.
*/
ANDROID_MEMBAR_FULL(); /* RELEASE BARRIER */
mvalue = __bionic_swap(mtype | shared | MUTEX_STATE_BITS_UNLOCKED, &mutex->value);
/* Wake one waiting thread, if any */
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) {
__futex_wake_ex(&mutex->value, shared, 1);
}
return 0;
}
int pthread_mutex_unlock(pthread_mutex_t *mutex)
{
#ifdef PTHREAD_DEBUG
if (PTHREAD_DEBUG_ENABLED) {
pthread_debug_mutex_unlock_check(mutex);
}
#endif
return pthread_mutex_unlock_impl(mutex);
}
__LIBC_HIDDEN__
int pthread_mutex_trylock_impl(pthread_mutex_t *mutex)
{
int mvalue, mtype, tid, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
mvalue = mutex->value;
mtype = (mvalue & MUTEX_TYPE_MASK);
shared = (mvalue & MUTEX_SHARED_MASK);
/* Handle common case first */
if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) )
{
if (__bionic_cmpxchg(shared|MUTEX_STATE_BITS_UNLOCKED,
shared|MUTEX_STATE_BITS_LOCKED_UNCONTENDED,
&mutex->value) == 0) {
ANDROID_MEMBAR_FULL();
return 0;
}
return EBUSY;
}
/* Do we already own this recursive or error-check mutex ? */
tid = __get_thread()->kernel_id;
if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
return _recursive_increment(mutex, mvalue, mtype);
/* Same as pthread_mutex_lock, except that we don't want to wait, and
* the only operation that can succeed is a single cmpxchg to acquire the
* lock if it is released / not owned by anyone. No need for a complex loop.
*/
mtype |= shared | MUTEX_STATE_BITS_UNLOCKED;
mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
if (__likely(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) {
ANDROID_MEMBAR_FULL();
return 0;
}
return EBUSY;
}
int pthread_mutex_trylock(pthread_mutex_t *mutex)
{
int err = pthread_mutex_trylock_impl(mutex);
#ifdef PTHREAD_DEBUG
if (PTHREAD_DEBUG_ENABLED) {
if (!err) {
pthread_debug_mutex_lock_check(mutex);
}
}
#endif
return err;
}
/* initialize 'ts' with the difference between 'abstime' and the current time
* according to 'clock'. Returns -1 if abstime already expired, or 0 otherwise.
*/
static int
__timespec_to_absolute(struct timespec* ts, const struct timespec* abstime, clockid_t clock)
{
clock_gettime(clock, ts);
ts->tv_sec = abstime->tv_sec - ts->tv_sec;
ts->tv_nsec = abstime->tv_nsec - ts->tv_nsec;
if (ts->tv_nsec < 0) {
ts->tv_sec--;
ts->tv_nsec += 1000000000;
}
if ((ts->tv_nsec < 0) || (ts->tv_sec < 0))
return -1;
return 0;
}
/* initialize 'abstime' to the current time according to 'clock' plus 'msecs'
* milliseconds.
*/
static void
__timespec_to_relative_msec(struct timespec* abstime, unsigned msecs, clockid_t clock)
{
clock_gettime(clock, abstime);
abstime->tv_sec += msecs/1000;
abstime->tv_nsec += (msecs%1000)*1000000;
if (abstime->tv_nsec >= 1000000000) {
abstime->tv_sec++;
abstime->tv_nsec -= 1000000000;
}
}
__LIBC_HIDDEN__
int pthread_mutex_lock_timeout_np_impl(pthread_mutex_t *mutex, unsigned msecs)
{
clockid_t clock = CLOCK_MONOTONIC;
struct timespec abstime;
struct timespec ts;
int mvalue, mtype, tid, shared;
/* compute absolute expiration time */
__timespec_to_relative_msec(&abstime, msecs, clock);
if (__unlikely(mutex == NULL))
return EINVAL;
mvalue = mutex->value;
mtype = (mvalue & MUTEX_TYPE_MASK);
shared = (mvalue & MUTEX_SHARED_MASK);
/* Handle common case first */
if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) )
{
const int unlocked = shared | MUTEX_STATE_BITS_UNLOCKED;
const int locked_uncontended = shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
const int locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED;
/* fast path for uncontended lock. Note: MUTEX_TYPE_BITS_NORMAL is 0 */
if (__bionic_cmpxchg(unlocked, locked_uncontended, &mutex->value) == 0) {
ANDROID_MEMBAR_FULL();
return 0;
}
/* loop while needed */
while (__bionic_swap(locked_contended, &mutex->value) != unlocked) {
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
__futex_wait_ex(&mutex->value, shared, locked_contended, &ts);
}
ANDROID_MEMBAR_FULL();
return 0;
}
/* Do we already own this recursive or error-check mutex ? */
tid = __get_thread()->kernel_id;
if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
return _recursive_increment(mutex, mvalue, mtype);
/* the following implements the same loop than pthread_mutex_lock_impl
* but adds checks to ensure that the operation never exceeds the
* absolute expiration time.
*/
mtype |= shared;
/* first try a quick lock */
if (mvalue == mtype) {
mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
if (__likely(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) {
ANDROID_MEMBAR_FULL();
return 0;
}
mvalue = mutex->value;
}
for (;;) {
struct timespec ts;
/* if the value is 'unlocked', try to acquire it directly */
/* NOTE: put state to 2 since we know there is contention */
if (mvalue == mtype) /* unlocked */ {
mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_CONTENDED;
if (__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0) {
ANDROID_MEMBAR_FULL();
return 0;
}
/* the value changed before we could lock it. We need to check
* the time to avoid livelocks, reload the value, then loop again. */
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
mvalue = mutex->value;
continue;
}
/* The value is locked. If 'uncontended', try to switch its state
* to 'contented' to ensure we get woken up later. */
if (MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(mvalue)) {
int newval = MUTEX_STATE_BITS_FLIP_CONTENTION(mvalue);
if (__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0) {
/* this failed because the value changed, reload it */
mvalue = mutex->value;
} else {
/* this succeeded, update mvalue */
mvalue = newval;
}
}
/* check time and update 'ts' */
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
/* Only wait to be woken up if the state is '2', otherwise we'll
* simply loop right now. This can happen when the second cmpxchg
* in our loop failed because the mutex was unlocked by another
* thread.
*/
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) {
if (__futex_wait_ex(&mutex->value, shared, mvalue, &ts) == ETIMEDOUT) {
return EBUSY;
}
mvalue = mutex->value;
}
}
/* NOTREACHED */
}
int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs)
{
int err = pthread_mutex_lock_timeout_np_impl(mutex, msecs);
#ifdef PTHREAD_DEBUG
if (PTHREAD_DEBUG_ENABLED) {
if (!err) {
pthread_debug_mutex_lock_check(mutex);
}
}
#endif
return err;
}
int pthread_mutex_destroy(pthread_mutex_t *mutex)
{
int ret;
/* use trylock to ensure that the mutex value is
* valid and is not already locked. */
ret = pthread_mutex_trylock_impl(mutex);
if (ret != 0)
return ret;
mutex->value = 0xdead10cc;
return 0;
}
int pthread_condattr_init(pthread_condattr_t *attr)
{
if (attr == NULL)
return EINVAL;
*attr = PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_condattr_getpshared(pthread_condattr_t *attr, int *pshared)
{
if (attr == NULL || pshared == NULL)
return EINVAL;
*pshared = *attr;
return 0;
}
int pthread_condattr_setpshared(pthread_condattr_t *attr, int pshared)
{
if (attr == NULL)
return EINVAL;
if (pshared != PTHREAD_PROCESS_SHARED &&
pshared != PTHREAD_PROCESS_PRIVATE)
return EINVAL;
*attr = pshared;
return 0;
}
int pthread_condattr_destroy(pthread_condattr_t *attr)
{
if (attr == NULL)
return EINVAL;
*attr = 0xdeada11d;
return 0;
}
/* We use one bit in condition variable values as the 'shared' flag
* The rest is a counter.
*/
#define COND_SHARED_MASK 0x0001
#define COND_COUNTER_INCREMENT 0x0002
#define COND_COUNTER_MASK (~COND_SHARED_MASK)
#define COND_IS_SHARED(c) (((c)->value & COND_SHARED_MASK) != 0)
/* XXX *technically* there is a race condition that could allow
* XXX a signal to be missed. If thread A is preempted in _wait()
* XXX after unlocking the mutex and before waiting, and if other
* XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
* XXX before thread A is scheduled again and calls futex_wait(),
* XXX then the signal will be lost.
*/
int pthread_cond_init(pthread_cond_t *cond,
const pthread_condattr_t *attr)
{
if (cond == NULL)
return EINVAL;
cond->value = 0;
if (attr != NULL && *attr == PTHREAD_PROCESS_SHARED)
cond->value |= COND_SHARED_MASK;
return 0;
}
int pthread_cond_destroy(pthread_cond_t *cond)
{
if (cond == NULL)
return EINVAL;
cond->value = 0xdeadc04d;
return 0;
}
/* This function is used by pthread_cond_broadcast and
* pthread_cond_signal to atomically decrement the counter
* then wake-up 'counter' threads.
*/
static int
__pthread_cond_pulse(pthread_cond_t *cond, int counter)
{
long flags;
if (__unlikely(cond == NULL))
return EINVAL;
flags = (cond->value & ~COND_COUNTER_MASK);
for (;;) {
long oldval = cond->value;
long newval = ((oldval - COND_COUNTER_INCREMENT) & COND_COUNTER_MASK)
| flags;
if (__bionic_cmpxchg(oldval, newval, &cond->value) == 0)
break;
}
/*
* Ensure that all memory accesses previously made by this thread are
* visible to the woken thread(s). On the other side, the "wait"
* code will issue any necessary barriers when locking the mutex.
*
* This may not strictly be necessary -- if the caller follows
* recommended practice and holds the mutex before signaling the cond
* var, the mutex ops will provide correct semantics. If they don't
* hold the mutex, they're subject to race conditions anyway.
*/
ANDROID_MEMBAR_FULL();
__futex_wake_ex(&cond->value, COND_IS_SHARED(cond), counter);
return 0;
}
int pthread_cond_broadcast(pthread_cond_t *cond)
{
return __pthread_cond_pulse(cond, INT_MAX);
}
int pthread_cond_signal(pthread_cond_t *cond)
{
return __pthread_cond_pulse(cond, 1);
}
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
return pthread_cond_timedwait(cond, mutex, NULL);
}
int __pthread_cond_timedwait_relative(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *reltime)
{
int status;
int oldvalue = cond->value;
pthread_mutex_unlock(mutex);
status = __futex_wait_ex(&cond->value, COND_IS_SHARED(cond), oldvalue, reltime);
pthread_mutex_lock(mutex);
if (status == (-ETIMEDOUT)) return ETIMEDOUT;
return 0;
}
int __pthread_cond_timedwait(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *abstime,
clockid_t clock)
{
struct timespec ts;
struct timespec * tsp;
if (abstime != NULL) {
if (__timespec_to_absolute(&ts, abstime, clock) < 0)
return ETIMEDOUT;
tsp = &ts;
} else {
tsp = NULL;
}
return __pthread_cond_timedwait_relative(cond, mutex, tsp);
}
int pthread_cond_timedwait(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
{
return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_REALTIME);
}
/* this one exists only for backward binary compatibility */
int pthread_cond_timedwait_monotonic(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
{
return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
}
int pthread_cond_timedwait_monotonic_np(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
{
return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
}
int pthread_cond_timedwait_relative_np(pthread_cond_t *cond,
pthread_mutex_t * mutex,
const struct timespec *reltime)
{
return __pthread_cond_timedwait_relative(cond, mutex, reltime);
}
int pthread_cond_timeout_np(pthread_cond_t *cond,
pthread_mutex_t * mutex,
unsigned msecs)
{
struct timespec ts;
ts.tv_sec = msecs / 1000;
ts.tv_nsec = (msecs % 1000) * 1000000;
return __pthread_cond_timedwait_relative(cond, mutex, &ts);
}
/* A technical note regarding our thread-local-storage (TLS) implementation:
*
* There can be up to TLSMAP_SIZE independent TLS keys in a given process,
* though the first TLSMAP_START keys are reserved for Bionic to hold
* special thread-specific variables like errno or a pointer to
* the current thread's descriptor.
*
* while stored in the TLS area, these entries cannot be accessed through
* pthread_getspecific() / pthread_setspecific() and pthread_key_delete()
*
* also, some entries in the key table are pre-allocated (see tlsmap_lock)
* to greatly simplify and speedup some OpenGL-related operations. though the
* initialy value will be NULL on all threads.
*
* you can use pthread_getspecific()/setspecific() on these, and in theory
* you could also call pthread_key_delete() as well, though this would
* probably break some apps.
*
* The 'tlsmap_t' type defined below implements a shared global map of
* currently created/allocated TLS keys and the destructors associated
* with them. You should use tlsmap_lock/unlock to access it to avoid
* any race condition.
*
* the global TLS map simply contains a bitmap of allocated keys, and
* an array of destructors.
*
* each thread has a TLS area that is a simple array of TLSMAP_SIZE void*
* pointers. the TLS area of the main thread is stack-allocated in
* __libc_init_common, while the TLS area of other threads is placed at
* the top of their stack in pthread_create.
*
* when pthread_key_create() is called, it finds the first free key in the
* bitmap, then set it to 1, saving the destructor altogether
*
* when pthread_key_delete() is called. it will erase the key's bitmap bit
* and its destructor, and will also clear the key data in the TLS area of
* all created threads. As mandated by Posix, it is the responsability of
* the caller of pthread_key_delete() to properly reclaim the objects that
* were pointed to by these data fields (either before or after the call).
*
*/
/* TLS Map implementation
*/
#define TLSMAP_START (TLS_SLOT_MAX_WELL_KNOWN+1)
#define TLSMAP_SIZE BIONIC_TLS_SLOTS
#define TLSMAP_BITS 32
#define TLSMAP_WORDS ((TLSMAP_SIZE+TLSMAP_BITS-1)/TLSMAP_BITS)
#define TLSMAP_WORD(m,k) (m)->map[(k)/TLSMAP_BITS]
#define TLSMAP_MASK(k) (1U << ((k)&(TLSMAP_BITS-1)))
/* this macro is used to quickly check that a key belongs to a reasonable range */
#define TLSMAP_VALIDATE_KEY(key) \
((key) >= TLSMAP_START && (key) < TLSMAP_SIZE)
/* the type of tls key destructor functions */
typedef void (*tls_dtor_t)(void*);
typedef struct {
int init; /* see comment in tlsmap_lock() */
uint32_t map[TLSMAP_WORDS]; /* bitmap of allocated keys */
tls_dtor_t dtors[TLSMAP_SIZE]; /* key destructors */
} tlsmap_t;
static pthread_mutex_t _tlsmap_lock = PTHREAD_MUTEX_INITIALIZER;
static tlsmap_t _tlsmap;
/* lock the global TLS map lock and return a handle to it */
static __inline__ tlsmap_t* tlsmap_lock(void)
{
tlsmap_t* m = &_tlsmap;
pthread_mutex_lock(&_tlsmap_lock);
/* we need to initialize the first entry of the 'map' array
* with the value TLS_DEFAULT_ALLOC_MAP. doing it statically
* when declaring _tlsmap is a bit awkward and is going to
* produce warnings, so do it the first time we use the map
* instead
*/
if (__unlikely(!m->init)) {
TLSMAP_WORD(m,0) = TLS_DEFAULT_ALLOC_MAP;
m->init = 1;
}
return m;
}
/* unlock the global TLS map */
static __inline__ void tlsmap_unlock(tlsmap_t* m)
{
pthread_mutex_unlock(&_tlsmap_lock);
(void)m; /* a good compiler is a happy compiler */
}
/* test to see wether a key is allocated */
static __inline__ int tlsmap_test(tlsmap_t* m, int key)
{
return (TLSMAP_WORD(m,key) & TLSMAP_MASK(key)) != 0;
}
/* set the destructor and bit flag on a newly allocated key */
static __inline__ void tlsmap_set(tlsmap_t* m, int key, tls_dtor_t dtor)
{
TLSMAP_WORD(m,key) |= TLSMAP_MASK(key);
m->dtors[key] = dtor;
}
/* clear the destructor and bit flag on an existing key */
static __inline__ void tlsmap_clear(tlsmap_t* m, int key)
{
TLSMAP_WORD(m,key) &= ~TLSMAP_MASK(key);
m->dtors[key] = NULL;
}
/* allocate a new TLS key, return -1 if no room left */
static int tlsmap_alloc(tlsmap_t* m, tls_dtor_t dtor)
{
int key;
for ( key = TLSMAP_START; key < TLSMAP_SIZE; key++ ) {
if ( !tlsmap_test(m, key) ) {
tlsmap_set(m, key, dtor);
return key;
}
}
return -1;
}
int pthread_key_create(pthread_key_t *key, void (*destructor_function)(void *))
{
uint32_t err = ENOMEM;
tlsmap_t* map = tlsmap_lock();
int k = tlsmap_alloc(map, destructor_function);
if (k >= 0) {
*key = k;
err = 0;
}
tlsmap_unlock(map);
return err;
}
/* This deletes a pthread_key_t. note that the standard mandates that this does
* not call the destructor of non-NULL key values. Instead, it is the
* responsibility of the caller to properly dispose of the corresponding data
* and resources, using any means it finds suitable.
*
* On the other hand, this function will clear the corresponding key data
* values in all known threads. this prevents later (invalid) calls to
* pthread_getspecific() to receive invalid/stale values.
*/
int pthread_key_delete(pthread_key_t key)
{
uint32_t err;
pthread_internal_t* thr;
tlsmap_t* map;
if (!TLSMAP_VALIDATE_KEY(key)) {
return EINVAL;
}
map = tlsmap_lock();
if (!tlsmap_test(map, key)) {
err = EINVAL;
goto err1;
}
/* clear value in all threads */
pthread_mutex_lock(&gThreadListLock);
for ( thr = gThreadList; thr != NULL; thr = thr->next ) {
/* avoid zombie threads with a negative 'join_count'. these are really
* already dead and don't have a TLS area anymore.
*
* similarly, it is possible to have thr->tls == NULL for threads that
* were just recently created through pthread_create() but whose
* startup trampoline (__thread_entry) hasn't been run yet by the
* scheduler. thr->tls will also be NULL after it's stack has been
* unmapped but before the ongoing pthread_join() is finished.
* so check for this too.
*/
if (thr->join_count < 0 || !thr->tls)
continue;
thr->tls[key] = NULL;
}
tlsmap_clear(map, key);
pthread_mutex_unlock(&gThreadListLock);
err = 0;
err1:
tlsmap_unlock(map);
return err;
}
int pthread_setspecific(pthread_key_t key, const void *ptr)
{
int err = EINVAL;
tlsmap_t* map;
if (TLSMAP_VALIDATE_KEY(key)) {
/* check that we're trying to set data for an allocated key */
map = tlsmap_lock();
if (tlsmap_test(map, key)) {
((uint32_t *)__get_tls())[key] = (uint32_t)ptr;
err = 0;
}
tlsmap_unlock(map);
}
return err;
}
void * pthread_getspecific(pthread_key_t key)
{
if (!TLSMAP_VALIDATE_KEY(key)) {
return NULL;
}
/* for performance reason, we do not lock/unlock the global TLS map
* to check that the key is properly allocated. if the key was not
* allocated, the value read from the TLS should always be NULL
* due to pthread_key_delete() clearing the values for all threads.
*/
return (void *)(((unsigned *)__get_tls())[key]);
}
/* Posix mandates that this be defined in <limits.h> but we don't have
* it just yet.
*/
#ifndef PTHREAD_DESTRUCTOR_ITERATIONS
# define PTHREAD_DESTRUCTOR_ITERATIONS 4
#endif
/* this function is called from pthread_exit() to remove all TLS key data
* from this thread's TLS area. this must call the destructor of all keys
* that have a non-NULL data value (and a non-NULL destructor).
*
* because destructors can do funky things like deleting/creating other
* keys, we need to implement this in a loop
*/
static void pthread_key_clean_all(void)
{
tlsmap_t* map;
void** tls = (void**)__get_tls();
int rounds = PTHREAD_DESTRUCTOR_ITERATIONS;
map = tlsmap_lock();
for (rounds = PTHREAD_DESTRUCTOR_ITERATIONS; rounds > 0; rounds--)
{
int kk, count = 0;
for (kk = TLSMAP_START; kk < TLSMAP_SIZE; kk++) {
if ( tlsmap_test(map, kk) )
{
void* data = tls[kk];
tls_dtor_t dtor = map->dtors[kk];
if (data != NULL && dtor != NULL)
{
/* we need to clear the key data now, this will prevent the
* destructor (or a later one) from seeing the old value if
* it calls pthread_getspecific() for some odd reason
*
* we do not do this if 'dtor == NULL' just in case another
* destructor function might be responsible for manually
* releasing the corresponding data.
*/
tls[kk] = NULL;
/* because the destructor is free to call pthread_key_create
* and/or pthread_key_delete, we need to temporarily unlock
* the TLS map
*/
tlsmap_unlock(map);
(*dtor)(data);
map = tlsmap_lock();
count += 1;
}
}
}
/* if we didn't call any destructor, there is no need to check the
* TLS data again
*/
if (count == 0)
break;
}
tlsmap_unlock(map);
}
// man says this should be in <linux/unistd.h>, but it isn't
extern int tgkill(int tgid, int tid, int sig);
int pthread_kill(pthread_t tid, int sig)
{
int ret;
int old_errno = errno;
pthread_internal_t * thread = (pthread_internal_t *)tid;
ret = tgkill(getpid(), thread->kernel_id, sig);
if (ret < 0) {
ret = errno;
errno = old_errno;
}
return ret;
}
int pthread_getcpuclockid(pthread_t tid, clockid_t *clockid)
{
const int CLOCK_IDTYPE_BITS = 3;
pthread_internal_t* thread = (pthread_internal_t*)tid;
if (!thread)
return ESRCH;
*clockid = CLOCK_THREAD_CPUTIME_ID | (thread->kernel_id << CLOCK_IDTYPE_BITS);
return 0;
}
/* NOTE: this implementation doesn't support a init function that throws a C++ exception
* or calls fork()
*/
int pthread_once( pthread_once_t* once_control, void (*init_routine)(void) )
{
volatile pthread_once_t* ocptr = once_control;
/* PTHREAD_ONCE_INIT is 0, we use the following bit flags
*
* bit 0 set -> initialization is under way
* bit 1 set -> initialization is complete
*/
#define ONCE_INITIALIZING (1 << 0)
#define ONCE_COMPLETED (1 << 1)
/* First check if the once is already initialized. This will be the common
* case and we want to make this as fast as possible. Note that this still
* requires a load_acquire operation here to ensure that all the
* stores performed by the initialization function are observable on
* this CPU after we exit.
*/
if (__likely((*ocptr & ONCE_COMPLETED) != 0)) {
ANDROID_MEMBAR_FULL();
return 0;
}
for (;;) {
/* Try to atomically set the INITIALIZING flag.
* This requires a cmpxchg loop, and we may need
* to exit prematurely if we detect that
* COMPLETED is now set.
*/
int32_t oldval, newval;
do {
oldval = *ocptr;
if ((oldval & ONCE_COMPLETED) != 0)
break;
newval = oldval | ONCE_INITIALIZING;
} while (__bionic_cmpxchg(oldval, newval, ocptr) != 0);
if ((oldval & ONCE_COMPLETED) != 0) {
/* We detected that COMPLETED was set while in our loop */
ANDROID_MEMBAR_FULL();
return 0;
}
if ((oldval & ONCE_INITIALIZING) == 0) {
/* We got there first, we can jump out of the loop to
* handle the initialization */
break;
}
/* Another thread is running the initialization and hasn't completed
* yet, so wait for it, then try again. */
__futex_wait_ex(ocptr, 0, oldval, NULL);
}
/* call the initialization function. */
(*init_routine)();
/* Do a store_release indicating that initialization is complete */
ANDROID_MEMBAR_FULL();
*ocptr = ONCE_COMPLETED;
/* Wake up any waiters, if any */
__futex_wake_ex(ocptr, 0, INT_MAX);
return 0;
}
/* This value is not exported by kernel headers, so hardcode it here */
#define MAX_TASK_COMM_LEN 16
#define TASK_COMM_FMT "/proc/self/task/%u/comm"
int pthread_setname_np(pthread_t thid, const char *thname)
{
size_t thname_len;
int saved_errno, ret;
if (thid == 0 || thname == NULL)
return EINVAL;
thname_len = strlen(thname);
if (thname_len >= MAX_TASK_COMM_LEN)
return ERANGE;
saved_errno = errno;
if (thid == pthread_self())
{
ret = prctl(PR_SET_NAME, (unsigned long)thname, 0, 0, 0) ? errno : 0;
}
else
{
/* Have to change another thread's name */
pthread_internal_t *thread = (pthread_internal_t *)thid;
char comm_name[sizeof(TASK_COMM_FMT) + 8];
ssize_t n;
int fd;
snprintf(comm_name, sizeof(comm_name), TASK_COMM_FMT, (unsigned int)thread->kernel_id);
fd = open(comm_name, O_RDWR);
if (fd == -1)
{
ret = errno;
goto exit;
}
n = TEMP_FAILURE_RETRY(write(fd, thname, thname_len));
close(fd);
if (n < 0)
ret = errno;
else if ((size_t)n != thname_len)
ret = EIO;
else
ret = 0;
}
exit:
errno = saved_errno;
return ret;
}
/* Return the kernel thread ID for a pthread.
* This is only defined for implementations where pthread <-> kernel is 1:1, which this is.
* Not the same as pthread_getthreadid_np, which is commonly defined to be opaque.
* Internal, not an NDK API.
*/
pid_t __pthread_gettid(pthread_t thid)
{
pthread_internal_t* thread = (pthread_internal_t*)thid;
return thread->kernel_id;
}
int __pthread_settid(pthread_t thid, pid_t tid)
{
if (thid == 0)
return EINVAL;
pthread_internal_t* thread = (pthread_internal_t*)thid;
thread->kernel_id = tid;
return 0;
}
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