/* * 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. */ #define LOG_TAG "AsynchronousSocketCloseMonitor" #include "AsynchronousSocketCloseMonitor.h" #include "cutils/log.h" #include <errno.h> #include <signal.h> #include <string.h> /** * We use an intrusive doubly-linked list to keep track of blocked threads. * This gives us O(1) insertion and removal, and means we don't need to do any allocation. * (The objects themselves are stack-allocated.) * Waking potentially-blocked threads when a socket is closed is O(n) in the total number of * blocked threads (not the number of threads actually blocked on the socket in question). * For now at least, this seems like a good compromise for Android. */ static pthread_mutex_t blockedThreadListMutex = PTHREAD_MUTEX_INITIALIZER; static AsynchronousSocketCloseMonitor* blockedThreadList = NULL; /** * The specific signal chosen here is arbitrary. */ #if defined(__APPLE__) static const int BLOCKED_THREAD_SIGNAL = SIGUSR2; #else static const int BLOCKED_THREAD_SIGNAL = SIGRTMIN + 2; #endif static void blockedThreadSignalHandler(int /*signal*/) { // Do nothing. We only sent this signal for its side-effect of interrupting syscalls. } void AsynchronousSocketCloseMonitor::init() { // Ensure that the signal we send interrupts system calls but doesn't kill threads. // Using sigaction(2) lets us ensure that the SA_RESTART flag is not set. // (The whole reason we're sending this signal is to unblock system calls!) struct sigaction sa; memset(&sa, 0, sizeof(sa)); sa.sa_handler = blockedThreadSignalHandler; sa.sa_flags = 0; int rc = sigaction(BLOCKED_THREAD_SIGNAL, &sa, NULL); if (rc == -1) { ALOGE("setting blocked thread signal handler failed: %s", strerror(errno)); } } void AsynchronousSocketCloseMonitor::signalBlockedThreads(int fd) { ScopedPthreadMutexLock lock(&blockedThreadListMutex); for (AsynchronousSocketCloseMonitor* it = blockedThreadList; it != NULL; it = it->mNext) { if (it->mFd == fd) { pthread_kill(it->mThread, BLOCKED_THREAD_SIGNAL); // Keep going, because there may be more than one thread... } } } AsynchronousSocketCloseMonitor::AsynchronousSocketCloseMonitor(int fd) { ScopedPthreadMutexLock lock(&blockedThreadListMutex); // Who are we, and what are we waiting for? mThread = pthread_self(); mFd = fd; // Insert ourselves at the head of the intrusive doubly-linked list... mPrev = NULL; mNext = blockedThreadList; if (mNext != NULL) { mNext->mPrev = this; } blockedThreadList = this; } AsynchronousSocketCloseMonitor::~AsynchronousSocketCloseMonitor() { ScopedPthreadMutexLock lock(&blockedThreadListMutex); // Unlink ourselves from the intrusive doubly-linked list... if (mNext != NULL) { mNext->mPrev = mPrev; } if (mPrev == NULL) { blockedThreadList = mNext; } else { mPrev->mNext = mNext; } }