Support looper callbacks based on smart pointers.

Bug: 6559630
Change-Id: I5a667f219f431838638acefbc9fa6afa610971bd

2 files changed, 88 insertions, 14 deletions

diff --git a/include/utils/Looper.h b/include/utils/Looper.h
index 84e3864a67..d4a0067fde 100644
--- a/include/utils/Looper.h
+++ b/include/utils/Looper.h
@@ -70,6 +70,9 @@ public:
  * A simple proxy that holds a weak reference to a message handler.
  */
 class WeakMessageHandler : public MessageHandler {
+protected:
+    virtual ~WeakMessageHandler();
+
 public:
     WeakMessageHandler(const wp<MessageHandler>& handler);
     virtual void handleMessage(const Message& message);
@@ -80,6 +83,43 @@ private:
 
 
 /**
+ * A looper callback.
+ */
+class LooperCallback : public virtual RefBase {
+protected:
+    virtual ~LooperCallback() { }
+
+public:
+    /**
+     * Handles a poll event for the given file descriptor.
+     * It is given the file descriptor it is associated with,
+     * a bitmask of the poll events that were triggered (typically ALOOPER_EVENT_INPUT),
+     * and the data pointer that was originally supplied.
+     *
+     * Implementations should return 1 to continue receiving callbacks, or 0
+     * to have this file descriptor and callback unregistered from the looper.
+     */
+    virtual int handleEvent(int fd, int events, void* data) = 0;
+};
+
+
+/**
+ * Wraps a ALooper_callbackFunc function pointer.
+ */
+class SimpleLooperCallback : public LooperCallback {
+protected:
+    virtual ~SimpleLooperCallback();
+
+public:
+    SimpleLooperCallback(ALooper_callbackFunc callback);
+    virtual int handleEvent(int fd, int events, void* data);
+
+private:
+    ALooper_callbackFunc mCallback;
+};
+
+
+/**
  * A polling loop that supports monitoring file descriptor events, optionally
  * using callbacks.  The implementation uses epoll() internally.
  *
@@ -159,7 +199,7 @@ public:
      * If the same file descriptor was previously added, it is replaced.
      *
      * "fd" is the file descriptor to be added.
-     * "ident" is an identifier for this event, which is returned from ALooper_pollOnce().
+     * "ident" is an identifier for this event, which is returned from pollOnce().
      * The identifier must be >= 0, or ALOOPER_POLL_CALLBACK if providing a non-NULL callback.
      * "events" are the poll events to wake up on.  Typically this is ALOOPER_EVENT_INPUT.
      * "callback" is the function to call when there is an event on the file descriptor.
@@ -179,8 +219,14 @@ public:
      *
      * This method can be called on any thread.
      * This method may block briefly if it needs to wake the poll.
+     *
+     * The callback may either be specified as a bare function pointer or as a smart
+     * pointer callback object.  The smart pointer should be preferred because it is
+     * easier to avoid races when the callback is removed from a different thread.
+     * See removeFd() for details.
      */
     int addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data);
+    int addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data);
 
     /**
      * Removes a previously added file descriptor from the looper.
@@ -193,6 +239,10 @@ public:
      * by returning 0 or by calling this method, then it can be guaranteed to not be invoked
      * again at any later time unless registered anew.
      *
+     * A simple way to avoid this problem is to use the version of addFd() that takes
+     * a sp<LooperCallback> instead of a bare function pointer.  The LooperCallback will
+     * be released at the appropriate time by the Looper.
+     *
      * Returns 1 if the file descriptor was removed, 0 if none was previously registered.
      *
      * This method can be called on any thread.
@@ -273,7 +323,7 @@ private:
     struct Request {
         int fd;
         int ident;
-        ALooper_callbackFunc callback;
+        sp<LooperCallback> callback;
         void* data;
     };
 
diff --git a/libs/utils/Looper.cpp b/libs/utils/Looper.cpp
index 9894993629..a5e66458c2 100644
--- a/libs/utils/Looper.cpp
+++ b/libs/utils/Looper.cpp
@@ -30,6 +30,9 @@ WeakMessageHandler::WeakMessageHandler(const wp<MessageHandler>& handler) :
         mHandler(handler) {
 }
 
+WeakMessageHandler::~WeakMessageHandler() {
+}
+
 void WeakMessageHandler::handleMessage(const Message& message) {
     sp<MessageHandler> handler = mHandler.promote();
     if (handler != NULL) {
@@ -38,6 +41,20 @@ void WeakMessageHandler::handleMessage(const Message& message) {
 }
 
 
+// --- SimpleLooperCallback ---
+
+SimpleLooperCallback::SimpleLooperCallback(ALooper_callbackFunc callback) :
+        mCallback(callback) {
+}
+
+SimpleLooperCallback::~SimpleLooperCallback() {
+}
+
+int SimpleLooperCallback::handleEvent(int fd, int events, void* data) {
+    return mCallback(fd, events, data);
+}
+
+
 // --- Looper ---
 
 // Hint for number of file descriptors to be associated with the epoll instance.
@@ -142,9 +159,8 @@ int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outDa
     for (;;) {
         while (mResponseIndex < mResponses.size()) {
             const Response& response = mResponses.itemAt(mResponseIndex++);
-            ALooper_callbackFunc callback = response.request.callback;
-            if (!callback) {
-                int ident = response.request.ident;
+            int ident = response.request.ident;
+            if (ident >= 0) {
                 int fd = response.request.fd;
                 int events = response.events;
                 void* data = response.request.data;
@@ -165,7 +181,7 @@ int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outDa
             ALOGD("%p ~ pollOnce - returning result %d", this, result);
 #endif
             if (outFd != NULL) *outFd = 0;
-            if (outEvents != NULL) *outEvents = NULL;
+            if (outEvents != NULL) *outEvents = 0;
             if (outData != NULL) *outData = NULL;
             return result;
         }
@@ -293,20 +309,22 @@ Done: ;
 
     // Invoke all response callbacks.
     for (size_t i = 0; i < mResponses.size(); i++) {
-        const Response& response = mResponses.itemAt(i);
-        ALooper_callbackFunc callback = response.request.callback;
-        if (callback) {
+        Response& response = mResponses.editItemAt(i);
+        if (response.request.ident == ALOOPER_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, callback, fd, events, data);
+                    this, response.request.callback.get(), fd, events, data);
 #endif
-            int callbackResult = callback(fd, events, data);
+            int callbackResult = response.request.callback->handleEvent(fd, events, data);
             if (callbackResult == 0) {
                 removeFd(fd);
             }
+            // 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 = ALOOPER_POLL_CALLBACK;
         }
     }
@@ -376,21 +394,27 @@ void Looper::pushResponse(int events, const Request& request) {
 }
 
 int Looper::addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data) {
+    return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);
+}
+
+int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
 #if DEBUG_CALLBACKS
     ALOGD("%p ~ addFd - fd=%d, ident=%d, events=0x%x, callback=%p, data=%p", this, fd, ident,
-            events, callback, data);
+            events, callback.get(), data);
 #endif
 
-    if (! callback) {
+    if (!callback.get()) {
         if (! mAllowNonCallbacks) {
             ALOGE("Invalid attempt to set NULL callback but not allowed for this looper.");
             return -1;
         }
 
         if (ident < 0) {
-            ALOGE("Invalid attempt to set NULL callback with ident <= 0.");
+            ALOGE("Invalid attempt to set NULL callback with ident < 0.");
             return -1;
         }
+    } else {
+        ident = ALOOPER_POLL_CALLBACK;
     }
 
     int epollEvents = 0;