/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef UTILS_LOOPER_H
#define UTILS_LOOPER_H
#include <utils/threads.h>
#include <utils/RefBase.h>
#include <utils/KeyedVector.h>
#include <utils/Timers.h>
#include <android/looper.h>
// When defined, uses epoll_wait() for polling, otherwise uses poll().
#define LOOPER_USES_EPOLL
// When defined, logs performance statistics for tuning and debugging purposes.
//#define LOOPER_STATISTICS
#ifdef LOOPER_USES_EPOLL
#include <sys/epoll.h>
#else
#include <sys/poll.h>
#endif
/*
* Declare a concrete type for the NDK's looper forward declaration.
*/
struct ALooper {
};
namespace android {
/**
* A polling loop that supports monitoring file descriptor events, optionally
* using callbacks. The implementation uses epoll() internally.
*
* A looper can be associated with a thread although there is no requirement that it must be.
*/
class Looper : public ALooper, public RefBase {
protected:
virtual ~Looper();
public:
/**
* Creates a looper.
*
* If allowNonCallbaks is true, the looper will allow file descriptors to be
* registered without associated callbacks. This assumes that the caller of
* pollOnce() is prepared to handle callback-less events itself.
*/
Looper(bool allowNonCallbacks);
/**
* Returns whether this looper instance allows the registration of file descriptors
* using identifiers instead of callbacks.
*/
bool getAllowNonCallbacks() const;
/**
* Waits for events to be available, with optional timeout in milliseconds.
* Invokes callbacks for all file descriptors on which an event occurred.
*
* If the timeout is zero, returns immediately without blocking.
* If the timeout is negative, waits indefinitely until an event appears.
*
* Returns ALOOPER_POLL_WAKE if the poll was awoken using wake() before
* the timeout expired and no callbacks were invoked and no other file
* descriptors were ready.
*
* Returns ALOOPER_POLL_CALLBACK if one or more callbacks were invoked.
*
* Returns ALOOPER_POLL_TIMEOUT if there was no data before the given
* timeout expired.
*
* Returns ALOOPER_POLL_ERROR if an error occurred.
*
* Returns a value >= 0 containing an identifier if its file descriptor has data
* and it has no callback function (requiring the caller here to handle it).
* In this (and only this) case outFd, outEvents and outData will contain the poll
* events and data associated with the fd, otherwise they will be set to NULL.
*
* This method does not return until it has finished invoking the appropriate callbacks
* for all file descriptors that were signalled.
*/
int pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData);
inline int pollOnce(int timeoutMillis) {
return pollOnce(timeoutMillis, NULL, NULL, NULL);
}
/**
* Like pollOnce(), but performs all pending callbacks until all
* data has been consumed or a file descriptor is available with no callback.
* This function will never return ALOOPER_POLL_CALLBACK.
*/
int pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData);
inline int pollAll(int timeoutMillis) {
return pollAll(timeoutMillis, NULL, NULL, NULL);
}
/**
* Wakes the poll asynchronously.
*
* This method can be called on any thread.
* This method returns immediately.
*/
void wake();
/**
* Adds a new file descriptor to be polled by the looper.
* If the same file descriptor was previously added, it is replaced.
*
* "fd" is the file descriptor to be added.
* "ident" is an identifier for this event, which is returned from ALooper_pollOnce().
* The identifier must be >= 0, or ALOOPER_POLL_CALLBACK if providing a non-NULL callback.
* "events" are the poll events to wake up on. Typically this is ALOOPER_EVENT_INPUT.
* "callback" is the function to call when there is an event on the file descriptor.
* "data" is a private data pointer to supply to the callback.
*
* There are two main uses of this function:
*
* (1) If "callback" is non-NULL, then this function will be called when there is
* data on the file descriptor. It should execute any events it has pending,
* appropriately reading from the file descriptor. The 'ident' is ignored in this case.
*
* (2) If "callback" is NULL, the 'ident' will be returned by ALooper_pollOnce
* when its file descriptor has data available, requiring the caller to take
* care of processing it.
*
* Returns 1 if the file descriptor was added, 0 if the arguments were invalid.
*
* This method can be called on any thread.
* This method may block briefly if it needs to wake the poll.
*/
int addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data);
/**
* Removes a previously added file descriptor from the looper.
*
* When this method returns, it is safe to close the file descriptor since the looper
* will no longer have a reference to it. However, it is possible for the callback to
* already be running or for it to run one last time if the file descriptor was already
* signalled. Calling code is responsible for ensuring that this case is safely handled.
* For example, if the callback takes care of removing itself during its own execution either
* by returning 0 or by calling this method, then it can be guaranteed to not be invoked
* again at any later time unless registered anew.
*
* Returns 1 if the file descriptor was removed, 0 if none was previously registered.
*
* This method can be called on any thread.
* This method may block briefly if it needs to wake the poll.
*/
int removeFd(int fd);
/**
* Prepares a looper associated with the calling thread, and returns it.
* If the thread already has a looper, it is returned. Otherwise, a new
* one is created, associated with the thread, and returned.
*
* The opts may be ALOOPER_PREPARE_ALLOW_NON_CALLBACKS or 0.
*/
static sp<Looper> prepare(int opts);
/**
* Sets the given looper to be associated with the calling thread.
* If another looper is already associated with the thread, it is replaced.
*
* If "looper" is NULL, removes the currently associated looper.
*/
static void setForThread(const sp<Looper>& looper);
/**
* Returns the looper associated with the calling thread, or NULL if
* there is not one.
*/
static sp<Looper> getForThread();
private:
struct Request {
int fd;
int ident;
ALooper_callbackFunc callback;
void* data;
};
struct Response {
int events;
Request request;
};
const bool mAllowNonCallbacks; // immutable
int mWakeReadPipeFd; // immutable
int mWakeWritePipeFd; // immutable
Mutex mLock;
#ifdef LOOPER_USES_EPOLL
int mEpollFd; // immutable
// Locked list of file descriptor monitoring requests.
KeyedVector<int, Request> mRequests; // guarded by mLock
#else
// The lock guards state used to track whether there is a poll() in progress and whether
// there are any other threads waiting in wakeAndLock(). The condition variables
// are used to transfer control among these threads such that all waiters are
// serviced before a new poll can begin.
// The wakeAndLock() method increments mWaiters, wakes the poll, blocks on mAwake
// until mPolling becomes false, then decrements mWaiters again.
// The poll() method blocks on mResume until mWaiters becomes 0, then sets
// mPolling to true, blocks until the poll completes, then resets mPolling to false
// and signals mResume if there are waiters.
bool mPolling; // guarded by mLock
uint32_t mWaiters; // guarded by mLock
Condition mAwake; // guarded by mLock
Condition mResume; // guarded by mLock
Vector<struct pollfd> mRequestedFds; // must hold mLock and mPolling must be false to modify
Vector<Request> mRequests; // must hold mLock and mPolling must be false to modify
ssize_t getRequestIndexLocked(int fd);
void wakeAndLock();
#endif
#ifdef LOOPER_STATISTICS
static const int SAMPLED_WAKE_CYCLES_TO_AGGREGATE = 100;
static const int SAMPLED_POLLS_TO_AGGREGATE = 1000;
nsecs_t mPendingWakeTime;
int mPendingWakeCount;
int mSampledWakeCycles;
int mSampledWakeCountSum;
nsecs_t mSampledWakeLatencySum;
int mSampledPolls;
int mSampledZeroPollCount;
int mSampledZeroPollLatencySum;
int mSampledTimeoutPollCount;
int mSampledTimeoutPollLatencySum;
#endif
// This state is only used privately by pollOnce and does not require a lock since
// it runs on a single thread.
Vector<Response> mResponses;
size_t mResponseIndex;
int pollInner(int timeoutMillis);
void awoken();
void pushResponse(int events, const Request& request);
static void initTLSKey();
static void threadDestructor(void *st);
};
} // namespace android
#endif // UTILS_LOOPER_H