replicant-frameworks_native/libs/utils/PollLoop.cpp
Dianne Hackborn 3c5d125ed7 Add new glue code for writing native apps.
This factors out the boiler-plate code from the sample
app to a common glue code that can be used for everyone
writing this style of app: a dedicated app thread that
takes care of waiting for events and processing them.

As part of doing this, ALooper has a new facility to allow
registration of fds that cause ALooper_pollOnce() to return
the fd that has data, allowing the app to drive the loop
without callbacks.  Hopefully this makes some people feel better. :)

Also do some other cleanup of the ALooper API, plus some
actual documentation.

Change-Id: Ic53bd56bdf627e3ba28a3c093faa06a92be522b8
2010-07-08 11:06:59 -07:00

365 lines
10 KiB
C++

//
// Copyright 2010 The Android Open Source Project
//
// A select loop implementation.
//
#define LOG_TAG "PollLoop"
//#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/PollLoop.h>
#include <unistd.h>
#include <fcntl.h>
namespace android {
static pthread_mutex_t gTLSMutex = PTHREAD_MUTEX_INITIALIZER;
static bool gHaveTLS = false;
static pthread_key_t gTLS = 0;
PollLoop::PollLoop(bool allowNonCallbacks) :
mAllowNonCallbacks(allowNonCallbacks), mPolling(false),
mWaiters(0), mPendingFdsPos(0) {
openWakePipe();
}
PollLoop::~PollLoop() {
closeWakePipe();
}
void PollLoop::threadDestructor(void *st) {
PollLoop* const self = static_cast<PollLoop*>(st);
if (self != NULL) {
self->decStrong((void*)threadDestructor);
}
}
void PollLoop::setForThread(const sp<PollLoop>& pollLoop) {
sp<PollLoop> old = getForThread();
if (pollLoop != NULL) {
pollLoop->incStrong((void*)threadDestructor);
}
pthread_setspecific(gTLS, pollLoop.get());
if (old != NULL) {
old->decStrong((void*)threadDestructor);
}
}
sp<PollLoop> PollLoop::getForThread() {
if (!gHaveTLS) {
pthread_mutex_lock(&gTLSMutex);
if (pthread_key_create(&gTLS, threadDestructor) != 0) {
pthread_mutex_unlock(&gTLSMutex);
return NULL;
}
gHaveTLS = true;
pthread_mutex_unlock(&gTLSMutex);
}
return (PollLoop*)pthread_getspecific(gTLS);
}
void PollLoop::openWakePipe() {
int wakeFds[2];
int result = pipe(wakeFds);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe. errno=%d", errno);
mWakeReadPipeFd = wakeFds[0];
mWakeWritePipeFd = wakeFds[1];
result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake read pipe non-blocking. errno=%d",
errno);
result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake write pipe non-blocking. errno=%d",
errno);
// Add the wake pipe to the head of the request list with a null callback.
struct pollfd requestedFd;
requestedFd.fd = mWakeReadPipeFd;
requestedFd.events = POLLIN;
mRequestedFds.insertAt(requestedFd, 0);
RequestedCallback requestedCallback;
requestedCallback.callback = NULL;
requestedCallback.looperCallback = NULL;
requestedCallback.data = NULL;
mRequestedCallbacks.insertAt(requestedCallback, 0);
}
void PollLoop::closeWakePipe() {
close(mWakeReadPipeFd);
close(mWakeWritePipeFd);
// Note: We don't need to remove the poll structure or callback entry because this
// method is currently only called by the destructor.
}
int32_t PollLoop::pollOnce(int timeoutMillis, int* outEvents, void** outData) {
// If there are still pending fds from the last call, dispatch those
// first, to avoid an earlier fd from starving later ones.
const size_t pendingFdsCount = mPendingFds.size();
if (mPendingFdsPos < pendingFdsCount) {
const PendingCallback& pending = mPendingFds.itemAt(mPendingFdsPos);
mPendingFdsPos++;
if (outEvents != NULL) *outEvents = pending.events;
if (outData != NULL) *outData = pending.data;
return pending.fd;
}
mLock.lock();
while (mWaiters != 0) {
mResume.wait(mLock);
}
mPolling = true;
mLock.unlock();
int32_t result;
size_t requestedCount = mRequestedFds.size();
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - waiting on %d fds", this, requestedCount);
for (size_t i = 0; i < requestedCount; i++) {
LOGD(" fd %d - events %d", mRequestedFds[i].fd, mRequestedFds[i].events);
}
#endif
int respondedCount = poll(mRequestedFds.editArray(), requestedCount, timeoutMillis);
if (respondedCount == 0) {
// Timeout
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - timeout", this);
#endif
result = POLL_TIMEOUT;
goto Done;
}
if (respondedCount < 0) {
// Error
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - error, errno=%d", this, errno);
#endif
if (errno != EINTR) {
LOGW("Poll failed with an unexpected error, errno=%d", errno);
}
result = POLL_ERROR;
goto Done;
}
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - handling responses from %d fds", this, respondedCount);
for (size_t i = 0; i < requestedCount; i++) {
LOGD(" fd %d - events %d, revents %d", mRequestedFds[i].fd, mRequestedFds[i].events,
mRequestedFds[i].revents);
}
#endif
mPendingCallbacks.clear();
mPendingFds.clear();
mPendingFdsPos = 0;
if (outEvents != NULL) *outEvents = 0;
if (outData != NULL) *outData = NULL;
result = POLL_CALLBACK;
for (size_t i = 0; i < requestedCount; i++) {
const struct pollfd& requestedFd = mRequestedFds.itemAt(i);
short revents = requestedFd.revents;
if (revents) {
const RequestedCallback& requestedCallback = mRequestedCallbacks.itemAt(i);
PendingCallback pending;
pending.fd = requestedFd.fd;
pending.events = revents;
pending.callback = requestedCallback.callback;
pending.looperCallback = requestedCallback.looperCallback;
pending.data = requestedCallback.data;
if (pending.callback || pending.looperCallback) {
mPendingCallbacks.push(pending);
} else if (pending.fd != mWakeReadPipeFd) {
if (result == POLL_CALLBACK) {
result = pending.fd;
if (outEvents != NULL) *outEvents = pending.events;
if (outData != NULL) *outData = pending.data;
} else {
mPendingFds.push(pending);
}
} else {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - awoken", this);
#endif
char buffer[16];
ssize_t nRead;
do {
nRead = read(mWakeReadPipeFd, buffer, sizeof(buffer));
} while (nRead == sizeof(buffer));
}
respondedCount -= 1;
if (respondedCount == 0) {
break;
}
}
}
Done:
mLock.lock();
mPolling = false;
if (mWaiters != 0) {
mAwake.broadcast();
}
mLock.unlock();
if (result == POLL_CALLBACK || result >= 0) {
size_t pendingCount = mPendingCallbacks.size();
for (size_t i = 0; i < pendingCount; i++) {
const PendingCallback& pendingCallback = mPendingCallbacks.itemAt(i);
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
LOGD("%p ~ pollOnce - invoking callback for fd %d", this, pendingCallback.fd);
#endif
bool keep = true;
if (pendingCallback.callback != NULL) {
keep = pendingCallback.callback(pendingCallback.fd, pendingCallback.events,
pendingCallback.data);
} else {
keep = pendingCallback.looperCallback(pendingCallback.fd, pendingCallback.events,
pendingCallback.data) != 0;
}
if (! keep) {
removeCallback(pendingCallback.fd);
}
}
}
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - done", this);
#endif
return result;
}
void PollLoop::wake() {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ wake", this);
#endif
ssize_t nWrite = write(mWakeWritePipeFd, "W", 1);
if (nWrite != 1) {
if (errno != EAGAIN) {
LOGW("Could not write wake signal, errno=%d", errno);
}
}
}
bool PollLoop::getAllowNonCallbacks() const {
return mAllowNonCallbacks;
}
void PollLoop::setCallback(int fd, int events, Callback callback, void* data) {
setCallbackCommon(fd, events, callback, NULL, data);
}
void PollLoop::setLooperCallback(int fd, int events, ALooper_callbackFunc* callback,
void* data) {
setCallbackCommon(fd, events, NULL, callback, data);
}
void PollLoop::setCallbackCommon(int fd, int events, Callback callback,
ALooper_callbackFunc* looperCallback, void* data) {
#if DEBUG_CALLBACKS
LOGD("%p ~ setCallback - fd=%d, events=%d", this, fd, events);
#endif
if (! events) {
LOGE("Invalid attempt to set a callback with no selected poll events.");
removeCallback(fd);
return;
}
if (! callback && ! looperCallback && ! mAllowNonCallbacks) {
LOGE("Invalid attempt to set NULL callback but not allowed.");
removeCallback(fd);
return;
}
wakeAndLock();
struct pollfd requestedFd;
requestedFd.fd = fd;
requestedFd.events = events;
RequestedCallback requestedCallback;
requestedCallback.callback = callback;
requestedCallback.looperCallback = looperCallback;
requestedCallback.data = data;
ssize_t index = getRequestIndexLocked(fd);
if (index < 0) {
mRequestedFds.push(requestedFd);
mRequestedCallbacks.push(requestedCallback);
} else {
mRequestedFds.replaceAt(requestedFd, size_t(index));
mRequestedCallbacks.replaceAt(requestedCallback, size_t(index));
}
mLock.unlock();
}
bool PollLoop::removeCallback(int fd) {
#if DEBUG_CALLBACKS
LOGD("%p ~ removeCallback - fd=%d", this, fd);
#endif
wakeAndLock();
ssize_t index = getRequestIndexLocked(fd);
if (index >= 0) {
mRequestedFds.removeAt(size_t(index));
mRequestedCallbacks.removeAt(size_t(index));
}
mLock.unlock();
return index >= 0;
}
ssize_t PollLoop::getRequestIndexLocked(int fd) {
size_t requestCount = mRequestedFds.size();
for (size_t i = 0; i < requestCount; i++) {
if (mRequestedFds.itemAt(i).fd == fd) {
return i;
}
}
return -1;
}
void PollLoop::wakeAndLock() {
mLock.lock();
mWaiters += 1;
while (mPolling) {
wake();
mAwake.wait(mLock);
}
mWaiters -= 1;
if (mWaiters == 0) {
mResume.signal();
}
}
} // namespace android