2d09171758
If the signal to dump a thread is never delivered, then it's possible for a deadlock. The signal handler is responsible for unlocking and deleting the ThreadEntry created for the pid/tid combination. This means if the signal is lost, the ThreadEntry gets stuck locked and never deleted. If a second attempt to get a backtrace of this thread occurs, there is a deadlock. Also, decrease the timeout from 10 seconds to 5 seconds. The original 10 seconds was because the unwind was actually done in the signal handler. Now the signal handler does nothing but copy the ucontext structure and let the caller do the unwind. Bug: 21086132 Change-Id: Idc735dbf6147ec879d35bd4f034c5d227e26a98d
131 lines
3.5 KiB
C++
131 lines
3.5 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <pthread.h>
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#include <stdint.h>
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#include <string.h>
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#include <sys/types.h>
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#include <time.h>
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#include <ucontext.h>
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#include "BacktraceLog.h"
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#include "ThreadEntry.h"
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// Initialize static member variables.
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ThreadEntry* ThreadEntry::list_ = nullptr;
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pthread_mutex_t ThreadEntry::list_mutex_ = PTHREAD_MUTEX_INITIALIZER;
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// Assumes that ThreadEntry::list_mutex_ has already been locked before
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// creating a ThreadEntry object.
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ThreadEntry::ThreadEntry(pid_t pid, pid_t tid)
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: pid_(pid), tid_(tid), ref_count_(1), mutex_(PTHREAD_MUTEX_INITIALIZER),
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wait_mutex_(PTHREAD_MUTEX_INITIALIZER), wait_value_(0),
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next_(ThreadEntry::list_), prev_(nullptr) {
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pthread_condattr_t attr;
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pthread_condattr_init(&attr);
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pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
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pthread_cond_init(&wait_cond_, &attr);
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// Add ourselves to the list.
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if (ThreadEntry::list_) {
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ThreadEntry::list_->prev_ = this;
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}
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ThreadEntry::list_ = this;
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}
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ThreadEntry* ThreadEntry::Get(pid_t pid, pid_t tid, bool create) {
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pthread_mutex_lock(&ThreadEntry::list_mutex_);
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ThreadEntry* entry = list_;
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while (entry != nullptr) {
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if (entry->Match(pid, tid)) {
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break;
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}
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entry = entry->next_;
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}
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if (!entry) {
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if (create) {
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entry = new ThreadEntry(pid, tid);
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}
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} else {
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entry->ref_count_++;
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}
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pthread_mutex_unlock(&ThreadEntry::list_mutex_);
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return entry;
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}
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void ThreadEntry::Remove(ThreadEntry* entry) {
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entry->Unlock();
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pthread_mutex_lock(&ThreadEntry::list_mutex_);
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if (--entry->ref_count_ == 0) {
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delete entry;
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}
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pthread_mutex_unlock(&ThreadEntry::list_mutex_);
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}
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// Assumes that ThreadEntry::list_mutex_ has already been locked before
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// deleting a ThreadEntry object.
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ThreadEntry::~ThreadEntry() {
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if (list_ == this) {
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list_ = next_;
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} else {
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if (next_) {
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next_->prev_ = prev_;
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}
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prev_->next_ = next_;
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}
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next_ = nullptr;
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prev_ = nullptr;
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pthread_cond_destroy(&wait_cond_);
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}
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bool ThreadEntry::Wait(int value) {
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timespec ts;
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clock_gettime(CLOCK_MONOTONIC, &ts);
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ts.tv_sec += 5;
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bool wait_completed = true;
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pthread_mutex_lock(&wait_mutex_);
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while (wait_value_ != value) {
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int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);
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if (ret != 0) {
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BACK_LOGW("pthread_cond_timedwait for value %d failed: %s", value, strerror(ret));
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wait_completed = false;
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break;
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}
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}
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pthread_mutex_unlock(&wait_mutex_);
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return wait_completed;
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}
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void ThreadEntry::Wake() {
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pthread_mutex_lock(&wait_mutex_);
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wait_value_++;
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pthread_mutex_unlock(&wait_mutex_);
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pthread_cond_signal(&wait_cond_);
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}
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void ThreadEntry::CopyUcontextFromSigcontext(void* sigcontext) {
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ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(sigcontext);
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// The only thing the unwinder cares about is the mcontext data.
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memcpy(&ucontext_.uc_mcontext, &ucontext->uc_mcontext, sizeof(ucontext->uc_mcontext));
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}
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