replicant-frameworks_native/libs/utils/Looper.cpp
Jeff Brown ed242de3f5 Reduce lock thrashing in native Looper.
In the common case, there is nothing interesting happening on the native
Looper besides occasional wake ups.  There is no point grabbing the
semaphore then.

Change-Id: Ib5c426d0e158dfa37891b7ff5537b6f833592fad
2010-09-17 17:01:23 -07:00

381 lines
12 KiB
C++

//
// 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 <unistd.h>
#include <fcntl.h>
#include <sys/epoll.h>
namespace android {
static pthread_mutex_t gTLSMutex = PTHREAD_MUTEX_INITIALIZER;
static bool gHaveTLS = false;
static pthread_key_t gTLS = 0;
// 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;
Looper::Looper(bool allowNonCallbacks) :
mAllowNonCallbacks(allowNonCallbacks),
mResponseIndex(0) {
mEpollFd = epoll_create(EPOLL_SIZE_HINT);
LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance. errno=%d", errno);
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);
struct epoll_event eventItem;
eventItem.events = EPOLLIN;
eventItem.data.fd = mWakeReadPipeFd;
result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, & eventItem);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake read pipe to epoll instance. errno=%d",
errno);
}
Looper::~Looper() {
close(mWakeReadPipeFd);
close(mWakeWritePipeFd);
close(mEpollFd);
}
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(gTLS, looper.get());
if (old != NULL) {
old->decStrong((void*)threadDestructor);
}
}
sp<Looper> Looper::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 (Looper*)pthread_getspecific(gTLS);
}
sp<Looper> Looper::prepare(int opts) {
bool allowNonCallbacks = opts & ALOOPER_PREPARE_ALLOW_NON_CALLBACKS;
sp<Looper> looper = Looper::getForThread();
if (looper == NULL) {
looper = new Looper(allowNonCallbacks);
Looper::setForThread(looper);
}
if (looper->getAllowNonCallbacks() != allowNonCallbacks) {
LOGW("Looper already prepared for this thread with a different value for the "
"ALOOPER_PREPARE_ALLOW_NON_CALLBACKS option.");
}
return looper;
}
bool Looper::getAllowNonCallbacks() const {
return mAllowNonCallbacks;
}
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++);
if (! response.request.callback) {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - returning signalled identifier %d: "
"fd=%d, events=0x%x, data=%p", this,
response.request.ident, response.request.fd,
response.events, response.request.data);
#endif
if (outFd != NULL) *outFd = response.request.fd;
if (outEvents != NULL) *outEvents = response.events;
if (outData != NULL) *outData = response.request.data;
return response.request.ident;
}
}
if (result != 0) {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - returning result %d", this, result);
#endif
if (outFd != NULL) *outFd = 0;
if (outEvents != NULL) *outEvents = NULL;
if (outData != NULL) *outData = NULL;
return result;
}
result = pollInner(timeoutMillis);
}
}
int Looper::pollInner(int timeoutMillis) {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - waiting: timeoutMillis=%d", this, timeoutMillis);
#endif
struct epoll_event eventItems[EPOLL_MAX_EVENTS];
int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);
if (eventCount < 0) {
if (errno == EINTR) {
return ALOOPER_POLL_WAKE;
}
LOGW("Poll failed with an unexpected error, errno=%d", errno);
return ALOOPER_POLL_ERROR;
}
if (eventCount == 0) {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - timeout", this);
#endif
return ALOOPER_POLL_TIMEOUT;
}
int result = ALOOPER_POLL_WAKE;
mResponses.clear();
mResponseIndex = 0;
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ pollOnce - handling events from %d fds", this, eventCount);
#endif
bool acquiredLock = false;
for (int i = 0; i < eventCount; i++) {
int fd = eventItems[i].data.fd;
uint32_t epollEvents = eventItems[i].events;
if (fd == mWakeReadPipeFd) {
if (epollEvents & EPOLLIN) {
#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 == -1 && errno == EINTR) || nRead == sizeof(buffer));
} else {
LOGW("Ignoring unexpected epoll events 0x%x on wake read pipe.", epollEvents);
}
} else {
if (! acquiredLock) {
mLock.lock();
acquiredLock = true;
}
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex >= 0) {
int events = 0;
if (epollEvents & EPOLLIN) events |= ALOOPER_EVENT_INPUT;
if (epollEvents & EPOLLOUT) events |= ALOOPER_EVENT_OUTPUT;
if (epollEvents & EPOLLERR) events |= ALOOPER_EVENT_ERROR;
if (epollEvents & EPOLLHUP) events |= ALOOPER_EVENT_HANGUP;
Response response;
response.events = events;
response.request = mRequests.valueAt(requestIndex);
mResponses.push(response);
} else {
LOGW("Ignoring unexpected epoll events 0x%x on fd %d that is "
"no longer registered.", epollEvents, fd);
}
}
}
if (acquiredLock) {
mLock.unlock();
}
for (size_t i = 0; i < mResponses.size(); i++) {
const Response& response = mResponses.itemAt(i);
if (response.request.callback) {
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
LOGD("%p ~ pollOnce - invoking callback: fd=%d, events=0x%x, data=%p", this,
response.request.fd, response.events, response.request.data);
#endif
int callbackResult = response.request.callback(
response.request.fd, response.events, response.request.data);
if (callbackResult == 0) {
removeFd(response.request.fd);
}
result = ALOOPER_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 == ALOOPER_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 != ALOOPER_POLL_CALLBACK) {
return result;
}
nsecs_t timeoutNanos = endTime - systemTime(SYSTEM_TIME_MONOTONIC);
if (timeoutNanos <= 0) {
return ALOOPER_POLL_TIMEOUT;
}
timeoutMillis = int(nanoseconds_to_milliseconds(timeoutNanos + 999999LL));
}
}
}
void Looper::wake() {
#if DEBUG_POLL_AND_WAKE
LOGD("%p ~ wake", this);
#endif
ssize_t nWrite;
do {
nWrite = write(mWakeWritePipeFd, "W", 1);
} while (nWrite == -1 && errno == EINTR);
if (nWrite != 1) {
if (errno != EAGAIN) {
LOGW("Could not write wake signal, errno=%d", errno);
}
}
}
int Looper::addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data) {
#if DEBUG_CALLBACKS
LOGD("%p ~ addFd - fd=%d, ident=%d, events=0x%x, callback=%p, data=%p", this, fd, ident,
events, callback, data);
#endif
int epollEvents = 0;
if (events & ALOOPER_EVENT_INPUT) epollEvents |= EPOLLIN;
if (events & ALOOPER_EVENT_OUTPUT) epollEvents |= EPOLLOUT;
if (events & ALOOPER_EVENT_ERROR) epollEvents |= EPOLLERR;
if (events & ALOOPER_EVENT_HANGUP) epollEvents |= EPOLLHUP;
if (epollEvents == 0) {
LOGE("Invalid attempt to set a callback with no selected poll events.");
return -1;
}
if (! callback) {
if (! mAllowNonCallbacks) {
LOGE("Invalid attempt to set NULL callback but not allowed for this looper.");
return -1;
}
if (ident < 0) {
LOGE("Invalid attempt to set NULL callback with ident <= 0.");
return -1;
}
}
{ // acquire lock
AutoMutex _l(mLock);
Request request;
request.fd = fd;
request.ident = ident;
request.callback = callback;
request.data = data;
struct epoll_event eventItem;
eventItem.events = epollEvents;
eventItem.data.fd = fd;
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
if (epollResult < 0) {
LOGE("Error adding epoll events for fd %d, errno=%d", fd, errno);
return -1;
}
mRequests.add(fd, request);
} else {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
if (epollResult < 0) {
LOGE("Error modifying epoll events for fd %d, errno=%d", fd, errno);
return -1;
}
mRequests.replaceValueAt(requestIndex, request);
}
} // release lock
return 1;
}
int Looper::removeFd(int fd) {
#if DEBUG_CALLBACKS
LOGD("%p ~ removeFd - fd=%d", this, fd);
#endif
{ // acquire lock
AutoMutex _l(mLock);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
return 0;
}
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_DEL, fd, NULL);
if (epollResult < 0) {
LOGE("Error removing epoll events for fd %d, errno=%d", fd, errno);
return -1;
}
mRequests.removeItemsAt(requestIndex);
} // request lock
return 1;
}
} // namespace android