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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 <poll.h>
namespace android {
/**
* A basic file descriptor polling loop based on poll() with callbacks.
*/
class PollLoop : public RefBase {
protected:
virtual ~PollLoop();
public:
PollLoop();
/**
* 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);
/**
* 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 true if a callback was invoked or if the loop was awoken by wake().
* Returns false if a timeout or error occurred.
*
* This method must only be called on the main thread.
* 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.
*/
bool pollOnce(int timeoutMillis);
/**
* Wakes the loop asynchronously.
*
* This method can be called on any thread.
* This method returns immediately.
*/
void wake();
/**
* 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 events, Callback callback, void* data = NULL);
/**
* 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);
private:
struct RequestedCallback {
Callback callback;
void* data;
};
struct PendingCallback {
int fd;
int events;
Callback callback;
void* data;
};
Mutex mLock;
Condition mAwake;
bool mPolling;
int mWakeReadPipeFd;
int mWakeWritePipeFd;
Vector<struct pollfd> mRequestedFds;
Vector<RequestedCallback> mRequestedCallbacks;
Vector<PendingCallback> mPendingCallbacks; // used privately by pollOnce
void openWakePipe();
void closeWakePipe();
ssize_t getRequestIndexLocked(int fd);
void wakeAndLock();
};
} // namespace android
#endif // UTILS_POLL_LOOP_H
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