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platform_system_core/libutils/Looper.cpp

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//
// Copyright 2010 The Android Open Source Project
//
// A looper implementation based on epoll().
//
#define LOG_TAG "Looper"
//#define LOG_NDEBUG 0
// Debugs poll and wake interactions.
#define DEBUG_POLL_AND_WAKE 0
// Debugs callback registration and invocation.
#define DEBUG_CALLBACKS 0
#include <cutils/log.h>
#include <utils/Looper.h>
#include <utils/Timers.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <inttypes.h>
#include <string.h>
#include <sys/eventfd.h>
#include <unistd.h>
namespace android {
// --- WeakMessageHandler ---
WeakMessageHandler::WeakMessageHandler(const wp<MessageHandler>& handler) :
mHandler(handler) {
}
WeakMessageHandler::~WeakMessageHandler() {
}
void WeakMessageHandler::handleMessage(const Message& message) {
sp<MessageHandler> handler = mHandler.promote();
if (handler != NULL) {
handler->handleMessage(message);
}
}
// --- SimpleLooperCallback ---
SimpleLooperCallback::SimpleLooperCallback(Looper_callbackFunc callback) :
mCallback(callback) {
}
SimpleLooperCallback::~SimpleLooperCallback() {
}
int SimpleLooperCallback::handleEvent(int fd, int events, void* data) {
return mCallback(fd, events, data);
}
// --- Looper ---
// Hint for number of file descriptors to be associated with the epoll instance.
static const int EPOLL_SIZE_HINT = 8;
// Maximum number of file descriptors for which to retrieve poll events each iteration.
static const int EPOLL_MAX_EVENTS = 16;
static pthread_once_t gTLSOnce = PTHREAD_ONCE_INIT;
static pthread_key_t gTLSKey = 0;
Looper::Looper(bool allowNonCallbacks) :
mAllowNonCallbacks(allowNonCallbacks), mSendingMessage(false),
mPolling(false), mEpollFd(-1), mEpollRebuildRequired(false),
mNextRequestSeq(0), mResponseIndex(0), mNextMessageUptime(LLONG_MAX) {
mWakeEventFd = eventfd(0, EFD_NONBLOCK);
LOG_ALWAYS_FATAL_IF(mWakeEventFd < 0, "Could not make wake event fd: %s",
strerror(errno));
AutoMutex _l(mLock);
rebuildEpollLocked();
}
Looper::~Looper() {
close(mWakeEventFd);
if (mEpollFd >= 0) {
close(mEpollFd);
}
}
void Looper::initTLSKey() {
int result = pthread_key_create(& gTLSKey, threadDestructor);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not allocate TLS key.");
}
void Looper::threadDestructor(void *st) {
Looper* const self = static_cast<Looper*>(st);
if (self != NULL) {
self->decStrong((void*)threadDestructor);
}
}
void Looper::setForThread(const sp<Looper>& looper) {
sp<Looper> old = getForThread(); // also has side-effect of initializing TLS
if (looper != NULL) {
looper->incStrong((void*)threadDestructor);
}
pthread_setspecific(gTLSKey, looper.get());
if (old != NULL) {
old->decStrong((void*)threadDestructor);
}
}
sp<Looper> Looper::getForThread() {
int result = pthread_once(& gTLSOnce, initTLSKey);
LOG_ALWAYS_FATAL_IF(result != 0, "pthread_once failed");
return (Looper*)pthread_getspecific(gTLSKey);
}
sp<Looper> Looper::prepare(int opts) {
bool allowNonCallbacks = opts & PREPARE_ALLOW_NON_CALLBACKS;
sp<Looper> looper = Looper::getForThread();
if (looper == NULL) {
looper = new Looper(allowNonCallbacks);
Looper::setForThread(looper);
}
if (looper->getAllowNonCallbacks() != allowNonCallbacks) {
ALOGW("Looper already prepared for this thread with a different value for the "
"LOOPER_PREPARE_ALLOW_NON_CALLBACKS option.");
}
return looper;
}
bool Looper::getAllowNonCallbacks() const {
return mAllowNonCallbacks;
}
void Looper::rebuildEpollLocked() {
// Close old epoll instance if we have one.
if (mEpollFd >= 0) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ rebuildEpollLocked - rebuilding epoll set", this);
#endif
close(mEpollFd);
}
// Allocate the new epoll instance and register the wake pipe.
mEpollFd = epoll_create(EPOLL_SIZE_HINT);
LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance: %s", strerror(errno));
struct epoll_event eventItem;
memset(& eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
eventItem.events = EPOLLIN;
eventItem.data.fd = mWakeEventFd;
int result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeEventFd, & eventItem);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake event fd to epoll instance: %s",
strerror(errno));
for (size_t i = 0; i < mRequests.size(); i++) {
const Request& request = mRequests.valueAt(i);
struct epoll_event eventItem;
request.initEventItem(&eventItem);
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, request.fd, & eventItem);
if (epollResult < 0) {
ALOGE("Error adding epoll events for fd %d while rebuilding epoll set: %s",
request.fd, strerror(errno));
}
}
}
void Looper::scheduleEpollRebuildLocked() {
if (!mEpollRebuildRequired) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ scheduleEpollRebuildLocked - scheduling epoll set rebuild", this);
#endif
mEpollRebuildRequired = true;
wake();
}
}
int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData) {
int result = 0;
for (;;) {
while (mResponseIndex < mResponses.size()) {
const Response& response = mResponses.itemAt(mResponseIndex++);
int ident = response.request.ident;
if (ident >= 0) {
int fd = response.request.fd;
int events = response.events;
void* data = response.request.data;
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - returning signalled identifier %d: "
"fd=%d, events=0x%x, data=%p",
this, ident, fd, events, data);
#endif
if (outFd != NULL) *outFd = fd;
if (outEvents != NULL) *outEvents = events;
if (outData != NULL) *outData = data;
return ident;
}
}
if (result != 0) {
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - returning result %d", this, result);
#endif
if (outFd != NULL) *outFd = 0;
if (outEvents != NULL) *outEvents = 0;
if (outData != NULL) *outData = NULL;
return result;
}
result = pollInner(timeoutMillis);
}
}
int Looper::pollInner(int timeoutMillis) {
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - waiting: timeoutMillis=%d", this, timeoutMillis);
#endif
// Adjust the timeout based on when the next message is due.
if (timeoutMillis != 0 && mNextMessageUptime != LLONG_MAX) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
int messageTimeoutMillis = toMillisecondTimeoutDelay(now, mNextMessageUptime);
if (messageTimeoutMillis >= 0
&& (timeoutMillis < 0 || messageTimeoutMillis < timeoutMillis)) {
timeoutMillis = messageTimeoutMillis;
}
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - next message in %" PRId64 "ns, adjusted timeout: timeoutMillis=%d",
this, mNextMessageUptime - now, timeoutMillis);
#endif
}
// Poll.
int result = POLL_WAKE;
mResponses.clear();
mResponseIndex = 0;
// We are about to idle.
mPolling = true;
struct epoll_event eventItems[EPOLL_MAX_EVENTS];
int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);
// No longer idling.
mPolling = false;
// Acquire lock.
mLock.lock();
// Rebuild epoll set if needed.
if (mEpollRebuildRequired) {
mEpollRebuildRequired = false;
rebuildEpollLocked();
goto Done;
}
// Check for poll error.
if (eventCount < 0) {
if (errno == EINTR) {
goto Done;
}
ALOGW("Poll failed with an unexpected error: %s", strerror(errno));
result = POLL_ERROR;
goto Done;
}
// Check for poll timeout.
if (eventCount == 0) {
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - timeout", this);
#endif
result = POLL_TIMEOUT;
goto Done;
}
// Handle all events.
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ pollOnce - handling events from %d fds", this, eventCount);
#endif
for (int i = 0; i < eventCount; i++) {
int fd = eventItems[i].data.fd;
uint32_t epollEvents = eventItems[i].events;
if (fd == mWakeEventFd) {
if (epollEvents & EPOLLIN) {
awoken();
} else {
ALOGW("Ignoring unexpected epoll events 0x%x on wake event fd.", epollEvents);
}
} else {
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex >= 0) {
int events = 0;
if (epollEvents & EPOLLIN) events |= EVENT_INPUT;
if (epollEvents & EPOLLOUT) events |= EVENT_OUTPUT;
if (epollEvents & EPOLLERR) events |= EVENT_ERROR;
if (epollEvents & EPOLLHUP) events |= EVENT_HANGUP;
pushResponse(events, mRequests.valueAt(requestIndex));
} else {
ALOGW("Ignoring unexpected epoll events 0x%x on fd %d that is "
"no longer registered.", epollEvents, fd);
}
}
}
Done: ;
// Invoke pending message callbacks.
mNextMessageUptime = LLONG_MAX;
while (mMessageEnvelopes.size() != 0) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(0);
if (messageEnvelope.uptime <= now) {
// Remove the envelope from the list.
// We keep a strong reference to the handler until the call to handleMessage
// finishes. Then we drop it so that the handler can be deleted *before*
// we reacquire our lock.
{ // obtain handler
sp<MessageHandler> handler = messageEnvelope.handler;
Message message = messageEnvelope.message;
mMessageEnvelopes.removeAt(0);
mSendingMessage = true;
mLock.unlock();
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
ALOGD("%p ~ pollOnce - sending message: handler=%p, what=%d",
this, handler.get(), message.what);
#endif
handler->handleMessage(message);
} // release handler
mLock.lock();
mSendingMessage = false;
result = POLL_CALLBACK;
} else {
// The last message left at the head of the queue determines the next wakeup time.
mNextMessageUptime = messageEnvelope.uptime;
break;
}
}
// Release lock.
mLock.unlock();
// Invoke all response callbacks.
for (size_t i = 0; i < mResponses.size(); i++) {
Response& response = mResponses.editItemAt(i);
if (response.request.ident == POLL_CALLBACK) {
int fd = response.request.fd;
int events = response.events;
void* data = response.request.data;
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
ALOGD("%p ~ pollOnce - invoking fd event callback %p: fd=%d, events=0x%x, data=%p",
this, response.request.callback.get(), fd, events, data);
#endif
// Invoke the callback. Note that the file descriptor may be closed by
// the callback (and potentially even reused) before the function returns so
// we need to be a little careful when removing the file descriptor afterwards.
int callbackResult = response.request.callback->handleEvent(fd, events, data);
if (callbackResult == 0) {
removeFd(fd, response.request.seq);
}
// Clear the callback reference in the response structure promptly because we
// will not clear the response vector itself until the next poll.
response.request.callback.clear();
result = POLL_CALLBACK;
}
}
return result;
}
int Looper::pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData) {
if (timeoutMillis <= 0) {
int result;
do {
result = pollOnce(timeoutMillis, outFd, outEvents, outData);
} while (result == POLL_CALLBACK);
return result;
} else {
nsecs_t endTime = systemTime(SYSTEM_TIME_MONOTONIC)
+ milliseconds_to_nanoseconds(timeoutMillis);
for (;;) {
int result = pollOnce(timeoutMillis, outFd, outEvents, outData);
if (result != POLL_CALLBACK) {
return result;
}
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
timeoutMillis = toMillisecondTimeoutDelay(now, endTime);
if (timeoutMillis == 0) {
return POLL_TIMEOUT;
}
}
}
}
void Looper::wake() {
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ wake", this);
#endif
uint64_t inc = 1;
ssize_t nWrite = TEMP_FAILURE_RETRY(write(mWakeEventFd, &inc, sizeof(uint64_t)));
if (nWrite != sizeof(uint64_t)) {
if (errno != EAGAIN) {
ALOGW("Could not write wake signal: %s", strerror(errno));
}
}
}
void Looper::awoken() {
#if DEBUG_POLL_AND_WAKE
ALOGD("%p ~ awoken", this);
#endif
uint64_t counter;
TEMP_FAILURE_RETRY(read(mWakeEventFd, &counter, sizeof(uint64_t)));
}
void Looper::pushResponse(int events, const Request& request) {
Response response;
response.events = events;
response.request = request;
mResponses.push(response);
}
int Looper::addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data) {
return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);
}
int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ addFd - fd=%d, ident=%d, events=0x%x, callback=%p, data=%p", this, fd, ident,
events, callback.get(), data);
#endif
if (!callback.get()) {
if (! mAllowNonCallbacks) {
ALOGE("Invalid attempt to set NULL callback but not allowed for this looper.");
return -1;
}
if (ident < 0) {
ALOGE("Invalid attempt to set NULL callback with ident < 0.");
return -1;
}
} else {
ident = POLL_CALLBACK;
}
{ // acquire lock
AutoMutex _l(mLock);
Request request;
request.fd = fd;
request.ident = ident;
request.events = events;
request.seq = mNextRequestSeq++;
request.callback = callback;
request.data = data;
if (mNextRequestSeq == -1) mNextRequestSeq = 0; // reserve sequence number -1
struct epoll_event eventItem;
request.initEventItem(&eventItem);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
if (epollResult < 0) {
ALOGE("Error adding epoll events for fd %d: %s", fd, strerror(errno));
return -1;
}
mRequests.add(fd, request);
} else {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
if (epollResult < 0) {
if (errno == ENOENT) {
// Tolerate ENOENT because it means that an older file descriptor was
// closed before its callback was unregistered and meanwhile a new
// file descriptor with the same number has been created and is now
// being registered for the first time. This error may occur naturally
// when a callback has the side-effect of closing the file descriptor
// before returning and unregistering itself. Callback sequence number
// checks further ensure that the race is benign.
//
// Unfortunately due to kernel limitations we need to rebuild the epoll
// set from scratch because it may contain an old file handle that we are
// now unable to remove since its file descriptor is no longer valid.
// No such problem would have occurred if we were using the poll system
// call instead, but that approach carries others disadvantages.
#if DEBUG_CALLBACKS
ALOGD("%p ~ addFd - EPOLL_CTL_MOD failed due to file descriptor "
"being recycled, falling back on EPOLL_CTL_ADD: %s",
this, strerror(errno));
#endif
epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
if (epollResult < 0) {
ALOGE("Error modifying or adding epoll events for fd %d: %s",
fd, strerror(errno));
return -1;
}
scheduleEpollRebuildLocked();
} else {
ALOGE("Error modifying epoll events for fd %d: %s", fd, strerror(errno));
return -1;
}
}
mRequests.replaceValueAt(requestIndex, request);
}
} // release lock
return 1;
}
int Looper::removeFd(int fd) {
return removeFd(fd, -1);
}
int Looper::removeFd(int fd, int seq) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ removeFd - fd=%d, seq=%d", this, fd, seq);
#endif
{ // acquire lock
AutoMutex _l(mLock);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
return 0;
}
// Check the sequence number if one was given.
if (seq != -1 && mRequests.valueAt(requestIndex).seq != seq) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ removeFd - sequence number mismatch, oldSeq=%d",
this, mRequests.valueAt(requestIndex).seq);
#endif
return 0;
}
// Always remove the FD from the request map even if an error occurs while
// updating the epoll set so that we avoid accidentally leaking callbacks.
mRequests.removeItemsAt(requestIndex);
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_DEL, fd, NULL);
if (epollResult < 0) {
if (seq != -1 && (errno == EBADF || errno == ENOENT)) {
// Tolerate EBADF or ENOENT when the sequence number is known because it
// means that the file descriptor was closed before its callback was
// unregistered. This error may occur naturally when a callback has the
// side-effect of closing the file descriptor before returning and
// unregistering itself.
//
// Unfortunately due to kernel limitations we need to rebuild the epoll
// set from scratch because it may contain an old file handle that we are
// now unable to remove since its file descriptor is no longer valid.
// No such problem would have occurred if we were using the poll system
// call instead, but that approach carries others disadvantages.
#if DEBUG_CALLBACKS
ALOGD("%p ~ removeFd - EPOLL_CTL_DEL failed due to file descriptor "
"being closed: %s", this, strerror(errno));
#endif
scheduleEpollRebuildLocked();
} else {
// Some other error occurred. This is really weird because it means
// our list of callbacks got out of sync with the epoll set somehow.
// We defensively rebuild the epoll set to avoid getting spurious
// notifications with nowhere to go.
ALOGE("Error removing epoll events for fd %d: %s", fd, strerror(errno));
scheduleEpollRebuildLocked();
return -1;
}
}
} // release lock
return 1;
}
void Looper::sendMessage(const sp<MessageHandler>& handler, const Message& message) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
sendMessageAtTime(now, handler, message);
}
void Looper::sendMessageDelayed(nsecs_t uptimeDelay, const sp<MessageHandler>& handler,
const Message& message) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
sendMessageAtTime(now + uptimeDelay, handler, message);
}
void Looper::sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
const Message& message) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ sendMessageAtTime - uptime=%" PRId64 ", handler=%p, what=%d",
this, uptime, handler.get(), message.what);
#endif
size_t i = 0;
{ // acquire lock
AutoMutex _l(mLock);
size_t messageCount = mMessageEnvelopes.size();
while (i < messageCount && uptime >= mMessageEnvelopes.itemAt(i).uptime) {
i += 1;
}
MessageEnvelope messageEnvelope(uptime, handler, message);
mMessageEnvelopes.insertAt(messageEnvelope, i, 1);
// Optimization: If the Looper is currently sending a message, then we can skip
// the call to wake() because the next thing the Looper will do after processing
// messages is to decide when the next wakeup time should be. In fact, it does
// not even matter whether this code is running on the Looper thread.
if (mSendingMessage) {
return;
}
} // release lock
// Wake the poll loop only when we enqueue a new message at the head.
if (i == 0) {
wake();
}
}
void Looper::removeMessages(const sp<MessageHandler>& handler) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ removeMessages - handler=%p", this, handler.get());
#endif
{ // acquire lock
AutoMutex _l(mLock);
for (size_t i = mMessageEnvelopes.size(); i != 0; ) {
const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(--i);
if (messageEnvelope.handler == handler) {
mMessageEnvelopes.removeAt(i);
}
}
} // release lock
}
void Looper::removeMessages(const sp<MessageHandler>& handler, int what) {
#if DEBUG_CALLBACKS
ALOGD("%p ~ removeMessages - handler=%p, what=%d", this, handler.get(), what);
#endif
{ // acquire lock
AutoMutex _l(mLock);
for (size_t i = mMessageEnvelopes.size(); i != 0; ) {
const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(--i);
if (messageEnvelope.handler == handler
&& messageEnvelope.message.what == what) {
mMessageEnvelopes.removeAt(i);
}
}
} // release lock
}
bool Looper::isPolling() const {
return mPolling;
}
void Looper::Request::initEventItem(struct epoll_event* eventItem) const {
int epollEvents = 0;
if (events & EVENT_INPUT) epollEvents |= EPOLLIN;
if (events & EVENT_OUTPUT) epollEvents |= EPOLLOUT;
memset(eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
eventItem->events = epollEvents;
eventItem->data.fd = fd;
}
} // namespace android
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