replicant-frameworks_native/include/utils/Looper.h
Jeff Brown b0619e8ad8 Looper: Drop default parameters in favor of a safer overload.
The idea is that if you're writing code that wants fd/events/data on
return from pollOnce() / pollAll() you should really pass in all of those
arguments.  When I changed the Looper API earlier, it was difficult
to ensure that all callers were passing the right parameters since they
were relying on default parameters to some degree so usage mistakes
would not have been caught by the compiler.

Change-Id: I1f2812894270aaf1515017ac1616b6b312d9b565
2010-09-16 18:51:15 -07:00

214 lines
7.6 KiB
C++

/*
* 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 <android/looper.h>
/*
* 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 mEpollFd; // immutable
int mWakeReadPipeFd; // immutable
int mWakeWritePipeFd; // immutable
// Locked list of file descriptor monitoring requests.
Mutex mLock;
KeyedVector<int, Request> mRequests;
// 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);
static void threadDestructor(void *st);
};
} // namespace android
#endif // UTILS_LOOPER_H