/*
* 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 <sys/epoll.h>
namespace android {
/*
* NOTE: Since Looper is used to implement the NDK ALooper, the Looper
* enums and the signature of Looper_callbackFunc need to align with
* that implementation.
*/
/**
* For callback-based event loops, this is the prototype of the function
* that is called when a file descriptor event occurs.
* It is given the file descriptor it is associated with,
* a bitmask of the poll events that were triggered (typically EVENT_INPUT),
* and the data pointer that was originally supplied.
*
* Implementations should return 1 to continue receiving callbacks, or 0
* to have this file descriptor and callback unregistered from the looper.
*/
typedef int (*Looper_callbackFunc)(int fd, int events, void* data);
/**
* A message that can be posted to a Looper.
*/
struct Message {
Message() : what(0) { }
Message(int what) : what(what) { }
/* The message type. (interpretation is left up to the handler) */
int what;
};
/**
* Interface for a Looper message handler.
*
* The Looper holds a strong reference to the message handler whenever it has
* a message to deliver to it. Make sure to call Looper::removeMessages
* to remove any pending messages destined for the handler so that the handler
* can be destroyed.
*/
class MessageHandler : public virtual RefBase {
protected:
virtual ~MessageHandler() { }
public:
/**
* Handles a message.
*/
virtual void handleMessage(const Message& message) = 0;
};
/**
* A simple proxy that holds a weak reference to a message handler.
*/
class WeakMessageHandler : public MessageHandler {
protected:
virtual ~WeakMessageHandler();
public:
WeakMessageHandler(const wp<MessageHandler>& handler);
virtual void handleMessage(const Message& message);
private:
wp<MessageHandler> mHandler;
};
/**
* A looper callback.
*/
class LooperCallback : public virtual RefBase {
protected:
virtual ~LooperCallback() { }
public:
/**
* Handles a poll event for the given file descriptor.
* It is given the file descriptor it is associated with,
* a bitmask of the poll events that were triggered (typically EVENT_INPUT),
* and the data pointer that was originally supplied.
*
* Implementations should return 1 to continue receiving callbacks, or 0
* to have this file descriptor and callback unregistered from the looper.
*/
virtual int handleEvent(int fd, int events, void* data) = 0;
};
/**
* Wraps a Looper_callbackFunc function pointer.
*/
class SimpleLooperCallback : public LooperCallback {
protected:
virtual ~SimpleLooperCallback();
public:
SimpleLooperCallback(Looper_callbackFunc callback);
virtual int handleEvent(int fd, int events, void* data);
private:
Looper_callbackFunc mCallback;
};
/**
* 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 RefBase {
protected:
virtual ~Looper();
public:
enum {
/**
* Result from Looper_pollOnce() and Looper_pollAll():
* The poll was awoken using wake() before the timeout expired
* and no callbacks were executed and no other file descriptors were ready.
*/
POLL_WAKE = -1,
/**
* Result from Looper_pollOnce() and Looper_pollAll():
* One or more callbacks were executed.
*/
POLL_CALLBACK = -2,
/**
* Result from Looper_pollOnce() and Looper_pollAll():
* The timeout expired.
*/
POLL_TIMEOUT = -3,
/**
* Result from Looper_pollOnce() and Looper_pollAll():
* An error occurred.
*/
POLL_ERROR = -4,
};
/**
* Flags for file descriptor events that a looper can monitor.
*
* These flag bits can be combined to monitor multiple events at once.
*/
enum {
/**
* The file descriptor is available for read operations.
*/
EVENT_INPUT = 1 << 0,
/**
* The file descriptor is available for write operations.
*/
EVENT_OUTPUT = 1 << 1,
/**
* The file descriptor has encountered an error condition.
*
* The looper always sends notifications about errors; it is not necessary
* to specify this event flag in the requested event set.
*/
EVENT_ERROR = 1 << 2,
/**
* The file descriptor was hung up.
* For example, indicates that the remote end of a pipe or socket was closed.
*
* The looper always sends notifications about hangups; it is not necessary
* to specify this event flag in the requested event set.
*/
EVENT_HANGUP = 1 << 3,
/**
* The file descriptor is invalid.
* For example, the file descriptor was closed prematurely.
*
* The looper always sends notifications about invalid file descriptors; it is not necessary
* to specify this event flag in the requested event set.
*/
EVENT_INVALID = 1 << 4,
};
enum {
/**
* Option for Looper_prepare: this looper will accept calls to
* Looper_addFd() that do not have a callback (that is provide NULL
* for the callback). In this case the caller of Looper_pollOnce()
* or Looper_pollAll() MUST check the return from these functions to
* discover when data is available on such fds and process it.
*/
PREPARE_ALLOW_NON_CALLBACKS = 1<<0
};
/**
* 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 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 POLL_CALLBACK if one or more callbacks were invoked.
*
* Returns POLL_TIMEOUT if there was no data before the given
* timeout expired.
*
* Returns 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 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 pollOnce().
* The identifier must be >= 0, or POLL_CALLBACK if providing a non-NULL callback.
* "events" are the poll events to wake up on. Typically this is 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 Looper_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.
*
* The callback may either be specified as a bare function pointer or as a smart
* pointer callback object. The smart pointer should be preferred because it is
* easier to avoid races when the callback is removed from a different thread.
* See removeFd() for details.
*/
int addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data);
int addFd(int fd, int ident, int events, const sp<LooperCallback>& 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.
*
* A simple way to avoid this problem is to use the version of addFd() that takes
* a sp<LooperCallback> instead of a bare function pointer. The LooperCallback will
* be released at the appropriate time by the Looper.
*
* 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);
/**
* Enqueues a message to be processed by the specified handler.
*
* The handler must not be null.
* This method can be called on any thread.
*/
void sendMessage(const sp<MessageHandler>& handler, const Message& message);
/**
* Enqueues a message to be processed by the specified handler after all pending messages
* after the specified delay.
*
* The time delay is specified in uptime nanoseconds.
* The handler must not be null.
* This method can be called on any thread.
*/
void sendMessageDelayed(nsecs_t uptimeDelay, const sp<MessageHandler>& handler,
const Message& message);
/**
* Enqueues a message to be processed by the specified handler after all pending messages
* at the specified time.
*
* The time is specified in uptime nanoseconds.
* The handler must not be null.
* This method can be called on any thread.
*/
void sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
const Message& message);
/**
* Removes all messages for the specified handler from the queue.
*
* The handler must not be null.
* This method can be called on any thread.
*/
void removeMessages(const sp<MessageHandler>& handler);
/**
* Removes all messages of a particular type for the specified handler from the queue.
*
* The handler must not be null.
* This method can be called on any thread.
*/
void removeMessages(const sp<MessageHandler>& handler, int what);
/**
* Returns whether this looper's thread is currently polling for more work to do.
* This is a good signal that the loop is still alive rather than being stuck
* handling a callback. Note that this method is intrinsically racy, since the
* state of the loop can change before you get the result back.
*/
bool isPolling() const;
/**
* 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 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;
int events;
int seq;
sp<LooperCallback> callback;
void* data;
void initEventItem(struct epoll_event* eventItem) const;
};
struct Response {
int events;
Request request;
};
struct MessageEnvelope {
MessageEnvelope() : uptime(0) { }
MessageEnvelope(nsecs_t uptime, const sp<MessageHandler> handler,
const Message& message) : uptime(uptime), handler(handler), message(message) {
}
nsecs_t uptime;
sp<MessageHandler> handler;
Message message;
};
const bool mAllowNonCallbacks; // immutable
int mWakeEventFd; // immutable
Mutex mLock;
Vector<MessageEnvelope> mMessageEnvelopes; // guarded by mLock
bool mSendingMessage; // guarded by mLock
// Whether we are currently waiting for work. Not protected by a lock,
// any use of it is racy anyway.
volatile bool mPolling;
int mEpollFd; // guarded by mLock but only modified on the looper thread
bool mEpollRebuildRequired; // guarded by mLock
// Locked list of file descriptor monitoring requests.
KeyedVector<int, Request> mRequests; // guarded by mLock
int mNextRequestSeq;
// 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;
nsecs_t mNextMessageUptime; // set to LLONG_MAX when none
int pollInner(int timeoutMillis);
int removeFd(int fd, int seq);
void awoken();
void pushResponse(int events, const Request& request);
void rebuildEpollLocked();
void scheduleEpollRebuildLocked();
static void initTLSKey();
static void threadDestructor(void *st);
static void initEpollEvent(struct epoll_event* eventItem);
};
} // namespace android
#endif // UTILS_LOOPER_H