Add new Looper API to check whether the looper is idle.

This is just to support the watchdog to give it a faster
way to determine if a thread is deadlocked without having
to post a message to it.

Change-Id: I068dc8b9387caf94fe5811fb4aeb0f9b57b1a080

include/utils/Looper.h

@@ -296,6 +296,13 @@ public:
      */
     void removeMessages(const sp<MessageHandler>& handler, int what);
 
+    /**
+     * Return whether this looper's thread is currently idling -- that is, whether it
+     * stopped waiting for more work to do.  Note that this is intrinsically racy, since
+     * its state can change before you get the result back.
+     */
+    bool isIdling() const;
+
     /**
      * Prepares a looper associated with the calling thread, and returns it.
      * If the thread already has a looper, it is returned.  Otherwise, a new
@@ -353,6 +360,10 @@ private:
     Vector<MessageEnvelope> mMessageEnvelopes; // guarded by mLock
     bool mSendingMessage; // guarded by mLock
 
+    // Whether we are currently waiting for work.  Not protected by a lock,
+    // any use of it is racy anyway.
+    volatile bool mIdling;
+
     int mEpollFd; // immutable
 
     // Locked list of file descriptor monitoring requests.

libs/utils/Looper.cpp

@@ -84,6 +84,8 @@ Looper::Looper(bool allowNonCallbacks) :
     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);
@@ -214,9 +216,15 @@ int Looper::pollInner(int timeoutMillis) {
     mResponses.clear();
     mResponseIndex = 0;
 
+    // We are about to idle.
+    mIdling = true;
+
     struct epoll_event eventItems[EPOLL_MAX_EVENTS];
     int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);
 
+    // No longer idling.
+    mIdling = false;
+
     // Acquire lock.
     mLock.lock();
 
@@ -558,4 +566,8 @@ void Looper::removeMessages(const sp<MessageHandler>& handler, int what) {
     } // release lock
 }
 
+bool Looper::isIdling() const {
+    return mIdling;
+}
+
 } // namespace android