Fix for bug 97866. Fixes async file I/O to ensure that we always call WaitOnThisThread if we're doing an async call (which does not wait if the notifier has already fired). Also don't bother checking return values from PBRead/WriteAsync, since they never fail, but do check the return value of the PBReadSync call. Fixes synchronization problems on Mac OS X. r=gordon, a=wtc.

nsprpub/pr/src/md/mac/macio.c

@@ -254,12 +254,13 @@ PRInt32 ReadWriteProc(PRFileDesc *fd, void *buf, PRUint32 bytes, IOOperation op)
 		}
 		
 		return (bytes);
-
 	}
 	else
 	{
 		static IOCompletionUPP	sCompletionUPP = NULL;
 		
+		PRBool  doingAsync = PR_FALSE;
+		
 		/* allocate the callback Universal Procedure Pointer (UPP). This actually allocates
 		   a 32 byte Ptr in the heap, so only do this once
 		*/
@@ -280,7 +281,9 @@ PRInt32 ReadWriteProc(PRFileDesc *fd, void *buf, PRUint32 bytes, IOOperation op)
 		/* 
 		** Issue the async read call and wait for the io semaphore associated
 		** with this thread.
-		** Don't compute error code from async call. Bug in OS returns a garbage value.
+		** Async file system calls *never* return error values, so ignore their
+		** results (see <http://developer.apple.com/technotes/fl/fl_515.html>);
+		** the completion routine is always called.
 		*/
 		me->io_fd = refNum;
 		me->md.osErrCode = noErr;
@@ -292,39 +295,33 @@ PRInt32 ReadWriteProc(PRFileDesc *fd, void *buf, PRUint32 bytes, IOOperation op)
 			*/
 			if ( bytes > 20480L )
 			{
-				err = PBReadAsync(&pbAsync.pb);
+				doingAsync = PR_TRUE;
+				me->io_pending = PR_TRUE;
+				
+				(void)PBReadAsync(&pbAsync.pb);
+			}
+			else
+			{
+				pbAsync.pb.ioParam.ioCompletion = NULL;
+				me->io_pending = PR_FALSE;
+				
+				err = PBReadSync(&pbAsync.pb);
 				if (err != noErr && err != eofErr)
 					goto ErrorExit;
-				
-	   			me->io_pending = PR_TRUE; /* Only mark thread io pending if async call worked */
-			}
-			else
-			{
-				(void) PBReadSync(&pbAsync.pb);
-				/*
-				** This is probbaly redundant but want to make sure we indicate the read
-				** is complete so we don't wander off into the Sargasso Sea of Mac
-				** threading
-				*/
-				pbAsync.pb.ioParam.ioResult = 0;
 			}
 		}
 		else
 		{
-			/* writes are currently always async */
-			err = PBWriteAsync(&pbAsync.pb);
-				if (err != noErr)
-					goto ErrorExit;
-			
-			/* Didn't get an error on the asyn call so mark thread io pending */
+			doingAsync = PR_TRUE;
 			me->io_pending = PR_TRUE;
+
+			/* writes are currently always async */
+			(void)PBWriteAsync(&pbAsync.pb);
 		}
 		
-		/* See if the i/o call is still pending before we actually yield */
-		if (pbAsync.pb.ioParam.ioResult == 1)
+		if (doingAsync) {
 			WaitOnThisThread(me, PR_INTERVAL_NO_TIMEOUT);
-		else
-			me->io_pending = PR_FALSE; /* io completed so don't mark thread io pending */
+		}
 	}
 	
 	err = me->md.osErrCode;
@@ -334,7 +331,7 @@ PRInt32 ReadWriteProc(PRFileDesc *fd, void *buf, PRUint32 bytes, IOOperation op)
 	err = pbAsync.pb.ioParam.ioResult;
 	if (err != noErr && err != eofErr)
 		goto ErrorExit;
-	else
+	
 	return pbAsync.pb.ioParam.ioActCount;
 
 ErrorExit: