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-rw-r--r--libutils/Looper.cpp229
1 files changed, 164 insertions, 65 deletions
diff --git a/libutils/Looper.cpp b/libutils/Looper.cpp
index 9a2dd6c..e69784d 100644
--- a/libutils/Looper.cpp
+++ b/libutils/Looper.cpp
@@ -20,6 +20,8 @@
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
+#include <inttypes.h>
+#include <sys/eventfd.h>
namespace android {
@@ -68,41 +70,20 @@ static pthread_key_t gTLSKey = 0;
Looper::Looper(bool allowNonCallbacks) :
mAllowNonCallbacks(allowNonCallbacks), mSendingMessage(false),
- mResponseIndex(0), mNextMessageUptime(LLONG_MAX) {
- int wakeFds[2];
- int result = pipe(wakeFds);
- LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe. errno=%d", errno);
+ 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. 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);
-
- mIdling = false;
-
- // Allocate the epoll instance and register the wake pipe.
- mEpollFd = epoll_create(EPOLL_SIZE_HINT);
- LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance. errno=%d", 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 = 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);
+ AutoMutex _l(mLock);
+ rebuildEpollLocked();
}
Looper::~Looper() {
- close(mWakeReadPipeFd);
- close(mWakeWritePipeFd);
- close(mEpollFd);
+ close(mWakeEventFd);
+ if (mEpollFd >= 0) {
+ close(mEpollFd);
+ }
}
void Looper::initTLSKey() {
@@ -156,6 +137,50 @@ 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. errno=%d", 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. errno=%d",
+ 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, errno=%d",
+ request.fd, 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 (;;) {
@@ -206,7 +231,7 @@ int Looper::pollInner(int timeoutMillis) {
timeoutMillis = messageTimeoutMillis;
}
#if DEBUG_POLL_AND_WAKE
- ALOGD("%p ~ pollOnce - next message in %lldns, adjusted timeout: timeoutMillis=%d",
+ ALOGD("%p ~ pollOnce - next message in %" PRId64 "ns, adjusted timeout: timeoutMillis=%d",
this, mNextMessageUptime - now, timeoutMillis);
#endif
}
@@ -217,17 +242,24 @@ int Looper::pollInner(int timeoutMillis) {
mResponseIndex = 0;
// We are about to idle.
- mIdling = true;
+ mPolling = true;
struct epoll_event eventItems[EPOLL_MAX_EVENTS];
int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);
// No longer idling.
- mIdling = false;
+ 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) {
@@ -255,11 +287,11 @@ int Looper::pollInner(int timeoutMillis) {
for (int i = 0; i < eventCount; i++) {
int fd = eventItems[i].data.fd;
uint32_t epollEvents = eventItems[i].events;
- if (fd == mWakeReadPipeFd) {
+ if (fd == mWakeEventFd) {
if (epollEvents & EPOLLIN) {
awoken();
} else {
- ALOGW("Ignoring unexpected epoll events 0x%x on wake read pipe.", epollEvents);
+ ALOGW("Ignoring unexpected epoll events 0x%x on wake event fd.", epollEvents);
}
} else {
ssize_t requestIndex = mRequests.indexOfKey(fd);
@@ -326,10 +358,14 @@ Done: ;
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);
+ 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();
@@ -370,12 +406,9 @@ void Looper::wake() {
ALOGD("%p ~ wake", this);
#endif
- ssize_t nWrite;
- do {
- nWrite = write(mWakeWritePipeFd, "W", 1);
- } while (nWrite == -1 && errno == EINTR);
-
- if (nWrite != 1) {
+ 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, errno=%d", errno);
}
@@ -387,11 +420,8 @@ void Looper::awoken() {
ALOGD("%p ~ awoken", this);
#endif
- char buffer[16];
- ssize_t nRead;
- do {
- nRead = read(mWakeReadPipeFd, buffer, sizeof(buffer));
- } while ((nRead == -1 && errno == EINTR) || nRead == sizeof(buffer));
+ uint64_t counter;
+ TEMP_FAILURE_RETRY(read(mWakeEventFd, &counter, sizeof(uint64_t)));
}
void Looper::pushResponse(int events, const Request& request) {
@@ -425,23 +455,20 @@ int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callb
ident = POLL_CALLBACK;
}
- int epollEvents = 0;
- if (events & EVENT_INPUT) epollEvents |= EPOLLIN;
- if (events & EVENT_OUTPUT) epollEvents |= EPOLLOUT;
-
{ // 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;
- memset(& eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
- eventItem.events = epollEvents;
- eventItem.data.fd = fd;
+ request.initEventItem(&eventItem);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
@@ -454,8 +481,36 @@ int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callb
} else {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
if (epollResult < 0) {
- ALOGE("Error modifying epoll events for fd %d, errno=%d", fd, errno);
- return -1;
+ 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, errno=%d",
+ this, errno);
+#endif
+ epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
+ if (epollResult < 0) {
+ ALOGE("Error modifying or adding epoll events for fd %d, errno=%d",
+ fd, errno);
+ return -1;
+ }
+ scheduleEpollRebuildLocked();
+ } else {
+ ALOGE("Error modifying epoll events for fd %d, errno=%d", fd, errno);
+ return -1;
+ }
}
mRequests.replaceValueAt(requestIndex, request);
}
@@ -464,8 +519,12 @@ int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callb
}
int Looper::removeFd(int fd) {
+ return removeFd(fd, -1);
+}
+
+int Looper::removeFd(int fd, int seq) {
#if DEBUG_CALLBACKS
- ALOGD("%p ~ removeFd - fd=%d", this, fd);
+ ALOGD("%p ~ removeFd - fd=%d, seq=%d", this, fd, seq);
#endif
{ // acquire lock
@@ -475,13 +534,43 @@ int Looper::removeFd(int fd) {
return 0;
}
- int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_DEL, fd, NULL);
- if (epollResult < 0) {
- ALOGE("Error removing epoll events for fd %d, errno=%d", fd, errno);
- return -1;
+ // 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, errno=%d", this, errno);
+#endif
+ scheduleEpollRebuildLocked();
+ } else {
+ ALOGE("Error removing epoll events for fd %d, errno=%d", fd, errno);
+ return -1;
+ }
+ }
} // release lock
return 1;
}
@@ -500,7 +589,7 @@ void Looper::sendMessageDelayed(nsecs_t uptimeDelay, const sp<MessageHandler>& h
void Looper::sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
const Message& message) {
#if DEBUG_CALLBACKS
- ALOGD("%p ~ sendMessageAtTime - uptime=%lld, handler=%p, what=%d",
+ ALOGD("%p ~ sendMessageAtTime - uptime=%" PRId64 ", handler=%p, what=%d",
this, uptime, handler.get(), message.what);
#endif
@@ -566,8 +655,18 @@ void Looper::removeMessages(const sp<MessageHandler>& handler, int what) {
} // release lock
}
-bool Looper::isIdling() const {
- return mIdling;
+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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