Add Thread::join

This new API will be used by applications that previously used the
lower-level pthread APIs (including pthread_join).  Centralizing on the
Thread class instead of pthread will permit additional functionality to
be added later in only one location.

Change-Id: I8460169ac9c61ac9f85752405ed54c94651058d7

include/utils/threads.h

@@ -510,6 +510,10 @@ public:
     // that case.
             status_t    requestExitAndWait();
 
+    // Wait until this object's thread exits. Returns immediately if not yet running.
+    // Do not call from this object's thread; will return WOULD_BLOCK in that case.
+            status_t    join();
+
 protected:
     // exitPending() returns true if requestExit() has been called.
             bool        exitPending() const;

libs/utils/Threads.cpp

@@ -846,6 +846,25 @@ status_t Thread::requestExitAndWait()
     return mStatus;
 }
 
+status_t Thread::join()
+{
+    Mutex::Autolock _l(mLock);
+    if (mThread == getThreadId()) {
+        LOGW(
+        "Thread (this=%p): don't call join() from this "
+        "Thread object's thread. It's a guaranteed deadlock!",
+        this);
+
+        return WOULD_BLOCK;
+    }
+
+    while (mRunning == true) {
+        mThreadExitedCondition.wait(mLock);
+    }
+
+    return mStatus;
+}
+
 bool Thread::exitPending() const
 {
     Mutex::Autolock _l(mLock);