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/*
* 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_POLL_LOOP_H
#define UTILS_POLL_LOOP_H
#include <utils/Vector.h>
#include <utils/threads.h>
#include <sys/poll.h>
#include <android/looper.h>
struct ALooper : public android::RefBase {
protected:
virtual ~ALooper() { }
public:
ALooper() { }
};
namespace android {
/**
* A basic file descriptor polling loop based on poll() with callbacks.
*/
class PollLoop : public ALooper {
protected:
virtual ~PollLoop();
public:
PollLoop(bool allowNonCallbacks);
/**
* A callback that it to be invoked when an event occurs on a file descriptor.
* Specifies the events that were triggered and the user data provided when the
* callback was set.
*
* Returns true if the callback should be kept, false if it should be removed automatically
* after the callback returns.
*/
typedef bool (*Callback)(int fd, int events, void* data);
enum {
POLL_CALLBACK = ALOOPER_POLL_CALLBACK,
POLL_TIMEOUT = ALOOPER_POLL_TIMEOUT,
POLL_ERROR = ALOOPER_POLL_ERROR,
};
/**
* Performs a single call to poll() 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 awoken.
*
* Returns ALOOPER_POLL_CALLBACK if a callback was invoked.
*
* Returns ALOOPER_POLL_TIMEOUT if there was no data before the given
* timeout expired.
*
* Returns ALOPER_POLL_ERROR if an error occurred.
*
* Returns a value >= 0 containing a file descriptor if it has data
* and it has no callback function (requiring the caller here to handle it).
* In this (and only this) case outEvents and outData will contain the poll
* events and data associated with the fd.
*
* This method must only be called on the thread owning the PollLoop.
* This method blocks until either a file descriptor is signalled, a timeout occurs,
* or wake() is called.
* This method does not return until it has finished invoking the appropriate callbacks
* for all file descriptors that were signalled.
*/
int32_t pollOnce(int timeoutMillis, int* outEvents = NULL, void** outData = NULL);
/**
* Wakes the loop asynchronously.
*
* This method can be called on any thread.
* This method returns immediately.
*/
void wake();
/**
* Control whether this PollLoop instance allows using IDs instead
* of callbacks.
*/
bool getAllowNonCallbacks() const;
/**
* Sets the callback for a file descriptor, replacing the existing one, if any.
* It is an error to call this method with events == 0 or callback == NULL.
*
* Note that a callback can be invoked with the POLLERR, POLLHUP or POLLNVAL events
* even if it is not explicitly requested when registered.
*
* This method can be called on any thread.
* This method may block briefly if it needs to wake the poll loop.
*/
void setCallback(int fd, int ident, int events, Callback callback, void* data = NULL);
/**
* Convenience for above setCallback when ident is not used. In this case
* the ident is set to POLL_CALLBACK.
*/
void setCallback(int fd, int events, Callback callback, void* data = NULL);
/**
* Like setCallback(), but for the NDK callback function.
*/
void setLooperCallback(int fd, int ident, int events, ALooper_callbackFunc* callback,
void* data);
/**
* Removes the callback for a file descriptor, if one exists.
*
* When this method returns, it is safe to close the file descriptor since the poll loop
* 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 false or calling this method, then it can be guaranteed to not be invoked
* again at any later time unless registered anew.
*
* This method can be called on any thread.
* This method may block briefly if it needs to wake the poll loop.
*
* Returns true if a callback was actually removed, false if none was registered.
*/
bool removeCallback(int fd);
/**
* Set the given PollLoop to be associated with the
* calling thread. There must be a 1:1 relationship between
* PollLoop and thread.
*/
static void setForThread(const sp<PollLoop>& pollLoop);
/**
* Return the PollLoop associated with the calling thread.
*/
static sp<PollLoop> getForThread();
private:
struct RequestedCallback {
Callback callback;
ALooper_callbackFunc* looperCallback;
int ident;
void* data;
};
struct PendingCallback {
int fd;
int ident;
int events;
Callback callback;
ALooper_callbackFunc* looperCallback;
void* data;
};
const bool mAllowNonCallbacks; // immutable
int mWakeReadPipeFd; // immutable
int mWakeWritePipeFd; // immutable
// 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.
Mutex mLock;
bool mPolling; // guarded by mLock
uint32_t mWaiters; // guarded by mLock
Condition mAwake; // guarded by mLock
Condition mResume; // guarded by mLock
// The next two vectors are only mutated when mPolling is false since they must
// not be changed while the poll() system call is in progress. To mutate these
// vectors, the poll() must first be awoken then the lock acquired.
Vector<struct pollfd> mRequestedFds;
Vector<RequestedCallback> mRequestedCallbacks;
// This state is only used privately by pollOnce and does not require a lock since
// it runs on a single thread.
Vector<PendingCallback> mPendingCallbacks;
Vector<PendingCallback> mPendingFds;
size_t mPendingFdsPos;
void openWakePipe();
void closeWakePipe();
void setCallbackCommon(int fd, int ident, int events, Callback callback,
ALooper_callbackFunc* looperCallback, void* data);
ssize_t getRequestIndexLocked(int fd);
void wakeAndLock();
static void threadDestructor(void *st);
};
} // namespace android
#endif // UTILS_POLL_LOOP_H
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