Asop 之 消息处理机制

public static void main(String[] args) {    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
    // CloseGuard defaults to true and can be quite spammy.  We    // disable it here, but selectively enable it later (via    // StrictMode) on debug builds, but using DropBox, not logs.    CloseGuard.setEnabled(false);
    Environment.initForCurrentUser();
    // Set the reporter for event logging in libcore    EventLogger.setReporter(new EventLoggingReporter());
    // Make sure TrustedCertificateStore looks in the right place for CA certificates    final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());    TrustedCertificateStore.setDefaultUserDirectory(configDir);
    Process.setArgV0("<pre-initialized>");
    Looper.prepareMainLooper();
    ActivityThread thread = new ActivityThread();    thread.attach(false);
    if (sMainThreadHandler == null) {        sMainThreadHandler = thread.getHandler();    }
    if (false) {        Looper.myLooper().setMessageLogging(new                LogPrinter(Log.DEBUG, "ActivityThread"));    }
    // End of event ActivityThreadMain.    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);    Looper.loop();
    throw new RuntimeException("Main thread loop unexpectedly exited");}

/** * Initialize the current thread as a looper, marking it as an * application's main looper. The main looper for your application * is created by the Android environment, so you should never need * to call this function yourself.  See also: {@link #prepare()} */public static void prepareMainLooper() {    prepare(false);    synchronized (Looper.class) {        if (sMainLooper != null) {            throw new IllegalStateException("The main Looper has already been prepared.");        }        sMainLooper = myLooper();    }}

private static void prepare(boolean quitAllowed) {    if (sThreadLocal.get() != null) {        throw new RuntimeException("Only one Looper may be created per thread");    }    sThreadLocal.set(new Looper(quitAllowed));}

public class MessageQueue {  ......    // True if the message queue can be quit.      private final boolean mQuitAllowed;      private int mPtr; // used by native code   private native void nativeInit();   MessageQueue(boolean quitAllowed) {        mQuitAllowed = quitAllowed;        mPtr = nativeInit();    }  ......}

static jlong android_os_MessageQueue_nativeInit(JNIEnv* env, jclass clazz) {    NativeMessageQueue* nativeMessageQueue = new NativeMessageQueue();    if (!nativeMessageQueue) {        jniThrowRuntimeException(env, "Unable to allocate native queue");        return 0;    }
    nativeMessageQueue->incStrong(env);    return reinterpret_cast<jlong>(nativeMessageQueue);}

NativeMessageQueue::NativeMessageQueue() :        mPollEnv(NULL), mPollObj(NULL), mExceptionObj(NULL) {    mLooper = Looper::getForThread();    if (mLooper == NULL) {        mLooper = new Looper(false);        Looper::setForThread(mLooper);    }}

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 | EFD_CLOEXEC);    LOG_ALWAYS_FATAL_IF(mWakeEventFd < 0, "Could not make wake event fd: %s",                        strerror(errno));
    AutoMutex _l(mLock);    rebuildEpollLocked();}

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));        }    }}

Message next() {    // Return here if the message loop has already quit and been disposed.    // This can happen if the application tries to restart a looper after quit    // which is not supported.    final long ptr = mPtr;    if (ptr == 0) {        return null;    }
    int pendingIdleHandlerCount = -1; // -1 only during first iteration    int nextPollTimeoutMillis = 0;    for (;;) {        if (nextPollTimeoutMillis != 0) {            Binder.flushPendingCommands();        }
        nativePollOnce(ptr, nextPollTimeoutMillis);
        synchronized (this) {            // Try to retrieve the next message.  Return if found.            final long now = SystemClock.uptimeMillis();            Message prevMsg = null;            Message msg = mMessages;            if (msg != null && msg.target == null) {                // Stalled by a barrier.  Find the next asynchronous message in the queue.                do {                    prevMsg = msg;                    msg = msg.next;                } while (msg != null && !msg.isAsynchronous());            }            if (msg != null) {                if (now < msg.when) {                    // Next message is not ready.  Set a timeout to wake up when it is ready.                    nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);                } else {                    // Got a message.                    mBlocked = false;                    if (prevMsg != null) {                        prevMsg.next = msg.next;                    } else {                        mMessages = msg.next;                    }                    msg.next = null;                    if (DEBUG) Log.v(TAG, "Returning message: " + msg);                    msg.markInUse();                    return msg;                }            } else {                // No more messages.                nextPollTimeoutMillis = -1;            }
            // Process the quit message now that all pending messages have been handled.            if (mQuitting) {                dispose();                return null;            }
            // If first time idle, then get the number of idlers to run.            // Idle handles only run if the queue is empty or if the first message            // in the queue (possibly a barrier) is due to be handled in the future.            if (pendingIdleHandlerCount < 0                    && (mMessages == null || now < mMessages.when)) {                pendingIdleHandlerCount = mIdleHandlers.size();            }            if (pendingIdleHandlerCount <= 0) {                // No idle handlers to run.  Loop and wait some more.                mBlocked = true;                continue;            }
            if (mPendingIdleHandlers == null) {                mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];            }            mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);        }
        // Run the idle handlers.        // We only ever reach this code block during the first iteration.        for (int i = 0; i < pendingIdleHandlerCount; i++) {            final IdleHandler idler = mPendingIdleHandlers[i];            mPendingIdleHandlers[i] = null; // release the reference to the handler
            boolean keep = false;            try {                keep = idler.queueIdle();            } catch (Throwable t) {                Log.wtf(TAG, "IdleHandler threw exception", t);            }
            if (!keep) {                synchronized (this) {                    mIdleHandlers.remove(idler);                }            }        }
        // Reset the idle handler count to 0 so we do not run them again.        pendingIdleHandlerCount = 0;
        // While calling an idle handler, a new message could have been delivered        // so go back and look again for a pending message without waiting.        nextPollTimeoutMillis = 0;    }}

static void android_os_MessageQueue_nativePollOnce(JNIEnv* env, jobject obj,        jlong ptr, jint timeoutMillis) {    NativeMessageQueue* nativeMessageQueue = reinterpret_cast<NativeMessageQueue*>(ptr);    nativeMessageQueue->pollOnce(env, obj, timeoutMillis);}

void NativeMessageQueue::pollOnce(JNIEnv* env, jobject pollObj, int timeoutMillis) {    mPollEnv = env;    mPollObj = pollObj;    mLooper->pollOnce(timeoutMillis);    mPollObj = NULL;    mPollEnv = NULL;
    if (mExceptionObj) {        env->Throw(mExceptionObj);        env->DeleteLocalRef(mExceptionObj);        mExceptionObj = NULL;    }}

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;}