487 lines
16 KiB
C++
487 lines
16 KiB
C++
/*
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* Copyright (C) 2010 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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#ifndef UTILS_LOOPER_H
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#define UTILS_LOOPER_H
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#include <utils/threads.h>
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#include <utils/RefBase.h>
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#include <utils/KeyedVector.h>
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#include <utils/Timers.h>
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#include <sys/epoll.h>
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namespace android {
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/*
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* NOTE: Since Looper is used to implement the NDK ALooper, the Looper
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* enums and the signature of Looper_callbackFunc need to align with
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* that implementation.
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*/
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/**
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* For callback-based event loops, this is the prototype of the function
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* that is called when a file descriptor event occurs.
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* It is given the file descriptor it is associated with,
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* a bitmask of the poll events that were triggered (typically EVENT_INPUT),
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* and the data pointer that was originally supplied.
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*
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* Implementations should return 1 to continue receiving callbacks, or 0
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* to have this file descriptor and callback unregistered from the looper.
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*/
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typedef int (*Looper_callbackFunc)(int fd, int events, void* data);
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/**
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* A message that can be posted to a Looper.
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*/
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struct Message {
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Message() : what(0) { }
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Message(int what) : what(what) { }
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/* The message type. (interpretation is left up to the handler) */
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int what;
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};
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/**
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* Interface for a Looper message handler.
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*
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* The Looper holds a strong reference to the message handler whenever it has
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* a message to deliver to it. Make sure to call Looper::removeMessages
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* to remove any pending messages destined for the handler so that the handler
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* can be destroyed.
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*/
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class MessageHandler : public virtual RefBase {
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protected:
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virtual ~MessageHandler() { }
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public:
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/**
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* Handles a message.
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*/
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virtual void handleMessage(const Message& message) = 0;
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};
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/**
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* A simple proxy that holds a weak reference to a message handler.
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*/
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class WeakMessageHandler : public MessageHandler {
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protected:
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virtual ~WeakMessageHandler();
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public:
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WeakMessageHandler(const wp<MessageHandler>& handler);
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virtual void handleMessage(const Message& message);
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private:
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wp<MessageHandler> mHandler;
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};
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/**
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* A looper callback.
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*/
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class LooperCallback : public virtual RefBase {
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protected:
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virtual ~LooperCallback() { }
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public:
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/**
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* Handles a poll event for the given file descriptor.
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* It is given the file descriptor it is associated with,
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* a bitmask of the poll events that were triggered (typically EVENT_INPUT),
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* and the data pointer that was originally supplied.
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*
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* Implementations should return 1 to continue receiving callbacks, or 0
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* to have this file descriptor and callback unregistered from the looper.
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*/
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virtual int handleEvent(int fd, int events, void* data) = 0;
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};
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/**
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* Wraps a Looper_callbackFunc function pointer.
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*/
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class SimpleLooperCallback : public LooperCallback {
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protected:
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virtual ~SimpleLooperCallback();
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public:
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SimpleLooperCallback(Looper_callbackFunc callback);
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virtual int handleEvent(int fd, int events, void* data);
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private:
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Looper_callbackFunc mCallback;
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};
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/**
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* A polling loop that supports monitoring file descriptor events, optionally
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* using callbacks. The implementation uses epoll() internally.
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*
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* A looper can be associated with a thread although there is no requirement that it must be.
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*/
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class Looper : public RefBase {
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protected:
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virtual ~Looper();
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public:
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enum {
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/**
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* Result from Looper_pollOnce() and Looper_pollAll():
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* The poll was awoken using wake() before the timeout expired
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* and no callbacks were executed and no other file descriptors were ready.
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*/
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POLL_WAKE = -1,
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/**
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* Result from Looper_pollOnce() and Looper_pollAll():
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* One or more callbacks were executed.
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*/
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POLL_CALLBACK = -2,
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/**
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* Result from Looper_pollOnce() and Looper_pollAll():
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* The timeout expired.
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*/
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POLL_TIMEOUT = -3,
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/**
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* Result from Looper_pollOnce() and Looper_pollAll():
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* An error occurred.
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*/
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POLL_ERROR = -4,
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};
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/**
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* Flags for file descriptor events that a looper can monitor.
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*
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* These flag bits can be combined to monitor multiple events at once.
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*/
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enum {
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/**
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* The file descriptor is available for read operations.
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*/
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EVENT_INPUT = 1 << 0,
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/**
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* The file descriptor is available for write operations.
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*/
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EVENT_OUTPUT = 1 << 1,
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/**
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* The file descriptor has encountered an error condition.
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*
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* The looper always sends notifications about errors; it is not necessary
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* to specify this event flag in the requested event set.
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*/
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EVENT_ERROR = 1 << 2,
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/**
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* The file descriptor was hung up.
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* For example, indicates that the remote end of a pipe or socket was closed.
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*
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* The looper always sends notifications about hangups; it is not necessary
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* to specify this event flag in the requested event set.
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*/
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EVENT_HANGUP = 1 << 3,
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/**
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* The file descriptor is invalid.
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* For example, the file descriptor was closed prematurely.
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*
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* The looper always sends notifications about invalid file descriptors; it is not necessary
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* to specify this event flag in the requested event set.
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*/
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EVENT_INVALID = 1 << 4,
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};
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enum {
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/**
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* Option for Looper_prepare: this looper will accept calls to
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* Looper_addFd() that do not have a callback (that is provide NULL
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* for the callback). In this case the caller of Looper_pollOnce()
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* or Looper_pollAll() MUST check the return from these functions to
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* discover when data is available on such fds and process it.
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*/
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PREPARE_ALLOW_NON_CALLBACKS = 1<<0
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};
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/**
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* Creates a looper.
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*
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* If allowNonCallbaks is true, the looper will allow file descriptors to be
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* registered without associated callbacks. This assumes that the caller of
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* pollOnce() is prepared to handle callback-less events itself.
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*/
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Looper(bool allowNonCallbacks);
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/**
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* Returns whether this looper instance allows the registration of file descriptors
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* using identifiers instead of callbacks.
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*/
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bool getAllowNonCallbacks() const;
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/**
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* Waits for events to be available, with optional timeout in milliseconds.
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* Invokes callbacks for all file descriptors on which an event occurred.
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*
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* If the timeout is zero, returns immediately without blocking.
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* If the timeout is negative, waits indefinitely until an event appears.
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*
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* Returns POLL_WAKE if the poll was awoken using wake() before
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* the timeout expired and no callbacks were invoked and no other file
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* descriptors were ready.
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*
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* Returns POLL_CALLBACK if one or more callbacks were invoked.
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*
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* Returns POLL_TIMEOUT if there was no data before the given
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* timeout expired.
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*
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* Returns POLL_ERROR if an error occurred.
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*
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* Returns a value >= 0 containing an identifier if its file descriptor has data
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* and it has no callback function (requiring the caller here to handle it).
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* In this (and only this) case outFd, outEvents and outData will contain the poll
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* events and data associated with the fd, otherwise they will be set to NULL.
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*
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* This method does not return until it has finished invoking the appropriate callbacks
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* for all file descriptors that were signalled.
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*/
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int pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData);
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inline int pollOnce(int timeoutMillis) {
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return pollOnce(timeoutMillis, NULL, NULL, NULL);
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}
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/**
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* Like pollOnce(), but performs all pending callbacks until all
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* data has been consumed or a file descriptor is available with no callback.
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* This function will never return POLL_CALLBACK.
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*/
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int pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData);
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inline int pollAll(int timeoutMillis) {
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return pollAll(timeoutMillis, NULL, NULL, NULL);
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}
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/**
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* Wakes the poll asynchronously.
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*
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* This method can be called on any thread.
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* This method returns immediately.
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*/
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void wake();
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/**
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* Adds a new file descriptor to be polled by the looper.
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* If the same file descriptor was previously added, it is replaced.
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*
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* "fd" is the file descriptor to be added.
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* "ident" is an identifier for this event, which is returned from pollOnce().
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* The identifier must be >= 0, or POLL_CALLBACK if providing a non-NULL callback.
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* "events" are the poll events to wake up on. Typically this is EVENT_INPUT.
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* "callback" is the function to call when there is an event on the file descriptor.
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* "data" is a private data pointer to supply to the callback.
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*
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* There are two main uses of this function:
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*
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* (1) If "callback" is non-NULL, then this function will be called when there is
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* data on the file descriptor. It should execute any events it has pending,
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* appropriately reading from the file descriptor. The 'ident' is ignored in this case.
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*
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* (2) If "callback" is NULL, the 'ident' will be returned by Looper_pollOnce
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* when its file descriptor has data available, requiring the caller to take
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* care of processing it.
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*
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* Returns 1 if the file descriptor was added, 0 if the arguments were invalid.
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*
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* This method can be called on any thread.
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* This method may block briefly if it needs to wake the poll.
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*
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* The callback may either be specified as a bare function pointer or as a smart
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* pointer callback object. The smart pointer should be preferred because it is
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* easier to avoid races when the callback is removed from a different thread.
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* See removeFd() for details.
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*/
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int addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data);
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int addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data);
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/**
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* Removes a previously added file descriptor from the looper.
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*
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* When this method returns, it is safe to close the file descriptor since the looper
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* will no longer have a reference to it. However, it is possible for the callback to
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* already be running or for it to run one last time if the file descriptor was already
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* signalled. Calling code is responsible for ensuring that this case is safely handled.
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* For example, if the callback takes care of removing itself during its own execution either
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* by returning 0 or by calling this method, then it can be guaranteed to not be invoked
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* again at any later time unless registered anew.
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*
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* A simple way to avoid this problem is to use the version of addFd() that takes
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* a sp<LooperCallback> instead of a bare function pointer. The LooperCallback will
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* be released at the appropriate time by the Looper.
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*
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* Returns 1 if the file descriptor was removed, 0 if none was previously registered.
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*
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* This method can be called on any thread.
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* This method may block briefly if it needs to wake the poll.
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*/
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int removeFd(int fd);
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/**
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* Enqueues a message to be processed by the specified handler.
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*
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* The handler must not be null.
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* This method can be called on any thread.
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*/
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void sendMessage(const sp<MessageHandler>& handler, const Message& message);
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/**
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* Enqueues a message to be processed by the specified handler after all pending messages
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* after the specified delay.
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*
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* The time delay is specified in uptime nanoseconds.
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* The handler must not be null.
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* This method can be called on any thread.
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*/
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void sendMessageDelayed(nsecs_t uptimeDelay, const sp<MessageHandler>& handler,
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const Message& message);
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/**
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* Enqueues a message to be processed by the specified handler after all pending messages
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* at the specified time.
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*
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* The time is specified in uptime nanoseconds.
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* The handler must not be null.
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* This method can be called on any thread.
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*/
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void sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
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const Message& message);
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/**
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* Removes all messages for the specified handler from the queue.
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*
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* The handler must not be null.
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* This method can be called on any thread.
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*/
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void removeMessages(const sp<MessageHandler>& handler);
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/**
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* Removes all messages of a particular type for the specified handler from the queue.
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*
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* The handler must not be null.
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* This method can be called on any thread.
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*/
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void removeMessages(const sp<MessageHandler>& handler, int what);
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/**
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* Returns whether this looper's thread is currently polling for more work to do.
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* This is a good signal that the loop is still alive rather than being stuck
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* handling a callback. Note that this method is intrinsically racy, since the
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* state of the loop can change before you get the result back.
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*/
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bool isPolling() const;
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/**
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* Prepares a looper associated with the calling thread, and returns it.
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* If the thread already has a looper, it is returned. Otherwise, a new
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* one is created, associated with the thread, and returned.
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*
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* The opts may be PREPARE_ALLOW_NON_CALLBACKS or 0.
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*/
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static sp<Looper> prepare(int opts);
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/**
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* Sets the given looper to be associated with the calling thread.
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* If another looper is already associated with the thread, it is replaced.
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*
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* If "looper" is NULL, removes the currently associated looper.
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*/
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static void setForThread(const sp<Looper>& looper);
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/**
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* Returns the looper associated with the calling thread, or NULL if
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* there is not one.
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*/
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static sp<Looper> getForThread();
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private:
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struct Request {
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int fd;
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int ident;
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int events;
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int seq;
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sp<LooperCallback> callback;
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void* data;
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void initEventItem(struct epoll_event* eventItem) const;
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};
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struct Response {
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int events;
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Request request;
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};
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struct MessageEnvelope {
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MessageEnvelope() : uptime(0) { }
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MessageEnvelope(nsecs_t uptime, const sp<MessageHandler> handler,
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const Message& message) : uptime(uptime), handler(handler), message(message) {
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}
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nsecs_t uptime;
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sp<MessageHandler> handler;
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Message message;
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};
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const bool mAllowNonCallbacks; // immutable
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int mWakeEventFd; // immutable
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Mutex mLock;
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Vector<MessageEnvelope> mMessageEnvelopes; // guarded by mLock
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bool mSendingMessage; // guarded by mLock
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// Whether we are currently waiting for work. Not protected by a lock,
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// any use of it is racy anyway.
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volatile bool mPolling;
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int mEpollFd; // guarded by mLock but only modified on the looper thread
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bool mEpollRebuildRequired; // guarded by mLock
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// Locked list of file descriptor monitoring requests.
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KeyedVector<int, Request> mRequests; // guarded by mLock
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int mNextRequestSeq;
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// This state is only used privately by pollOnce and does not require a lock since
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// it runs on a single thread.
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Vector<Response> mResponses;
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size_t mResponseIndex;
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nsecs_t mNextMessageUptime; // set to LLONG_MAX when none
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int pollInner(int timeoutMillis);
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int removeFd(int fd, int seq);
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void awoken();
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void pushResponse(int events, const Request& request);
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void rebuildEpollLocked();
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void scheduleEpollRebuildLocked();
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static void initTLSKey();
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static void threadDestructor(void *st);
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static void initEpollEvent(struct epoll_event* eventItem);
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};
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} // namespace android
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#endif // UTILS_LOOPER_H
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