Make sure io is flushed when driver is closed

Sometime when executing an tty io operation just before
the emulator terminated, the io message would get lost.
This commit makes sure that there is no io in the fd driver
before shutting down.

1 files changed, 74 insertions, 3 deletions

diff --git a/erts/emulator/sys/win32/sys.c b/erts/emulator/sys/win32/sys.c
index 6894d682e7..c4e748ed3c 100755
--- a/erts/emulator/sys/win32/sys.c
+++ b/erts/emulator/sys/win32/sys.c
@@ -420,6 +420,8 @@ typedef struct async_io {
   HANDLE ioAllowed;		/* The thread will wait for this event
 				 * before starting a new read or write.
 				 */
+  HANDLE flushEvent;		/* Used to signal that a flush should be done. */
+  HANDLE flushReplyEvent;	/* Used to signal that a flush has been done. */
   DWORD pendingError;		/* Used to delay presentating an error to Erlang
 				 * until the check_io function is entered.
 				 */
@@ -878,6 +880,8 @@ init_async_io(AsyncIo* aio, int use_threads)
     aio->ov.Offset = 0L;
     aio->ov.OffsetHigh = 0L;
     aio->ioAllowed = NULL;
+    aio->flushEvent = NULL;
+    aio->flushReplyEvent = NULL;
     aio->pendingError = 0;
     aio->bytesTransferred = 0;
 #ifdef ERTS_SMP
@@ -890,6 +894,12 @@ init_async_io(AsyncIo* aio, int use_threads)
 	aio->ioAllowed = CreateAutoEvent(FALSE);
 	if (aio->ioAllowed == NULL)
 	    return -1;
+	aio->flushEvent = CreateAutoEvent(FALSE);
+	if (aio->flushEvent == NULL)
+	  return -1;
+	aio->flushReplyEvent = CreateAutoEvent(FALSE);
+	if (aio->flushReplyEvent == NULL)
+	  return -1;
     }
     return 0;
 }
@@ -923,6 +933,14 @@ release_async_io(AsyncIo* aio, ErlDrvPort port_num)
     if (aio->ioAllowed != NULL)
 	CloseHandle(aio->ioAllowed);
     aio->ioAllowed = NULL;
+
+    if (aio->flushEvent != NULL)
+	CloseHandle(aio->flushEvent);
+    aio->flushEvent = NULL;
+
+    if (aio->flushReplyEvent != NULL)
+	CloseHandle(aio->flushReplyEvent);
+    aio->flushReplyEvent = NULL;
 }
 
 /* ----------------------------------------------------------------------
@@ -2083,16 +2101,26 @@ threaded_writer(LPVOID param)
     AsyncIo* aio = (AsyncIo *) param;
     HANDLE thread = GetCurrentThread();
     char* buf;
-    DWORD numToWrite;
+    DWORD numToWrite, handle;
     int ok;
+    HANDLE handles[2];
+    handles[0] = aio->ioAllowed;
+    handles[1] = aio->flushEvent;
   
     for (;;) {
-	WaitForSingleObject(aio->ioAllowed, INFINITE);
+	handle = WaitForMultipleObjects(2, handles, FALSE, INFINITE);
 	if (aio->flags & DF_EXIT_THREAD)
 	    break;
+
 	buf = OV_BUFFER_PTR(aio);
 	numToWrite = OV_NUM_TO_READ(aio);
 	aio->pendingError = 0;
+
+	if (handle == (WAIT_OBJECT_0 + 1) && numToWrite == 0) {
+	  SetEvent(aio->flushReplyEvent);
+	  continue;
+	}
+
 	ok = WriteFile(aio->fd, buf, numToWrite, &aio->bytesTransferred, NULL);
 	if (!ok) {
 	    aio->pendingError = GetLastError();
@@ -2127,7 +2155,11 @@ threaded_writer(LPVOID param)
 		}  
 	    }
 	}
-	SetEvent(aio->ov.hEvent);
+	OV_NUM_TO_READ(aio) = 0;
+	if (handle == (WAIT_OBJECT_0 + 1))
+	    SetEvent(aio->flushReplyEvent);
+	else
+	    SetEvent(aio->ov.hEvent);
 	if (aio->pendingError != NO_ERROR || aio->bytesTransferred == 0)
 	    break;
 	if (aio->flags & DF_EXIT_THREAD)
@@ -2193,6 +2225,43 @@ fd_start(ErlDrvPort port_num, char* name, SysDriverOpts* opts)
 	if ((dp = new_driver_data(port_num, opts->packet_bytes, 2, TRUE)) == NULL)
 	    return ERL_DRV_ERROR_GENERAL;
 	
+	/**
+	 * Here is a brief description about how the fd driver works on windows.
+	 *
+	 * fd_init:
+	 * For each in/out fd pair a threaded_reader and threaded_writer thread is
+	 * created. Within the DriverData struct each of the threads have an AsyncIO
+	 * sctruct associated with it.  Within AsyncIO there are two important HANDLEs,
+	 * ioAllowed and ov.hEvent. ioAllowed is used to signal the threaded_* threads
+	 * should read/write some data, and ov.hEvent is driver_select'ed to be used to
+	 * signal that the thread is done reading/writing.
+	 *
+	 * The reason for the driver being threaded like this is because once the FD is open
+	 * on windows, it is not possible to set the it in overlapped mode. So we have to
+	 * simulate this using threads.
+	 *
+	 * output:
+	 * When an output occurs the data to be outputted is copied to AsyncIO.ov. Then
+	 * the ioAllowed HANDLE is set, ov.hEvent is cleared and the port is marked as busy.
+	 * The threaded_writer thread is lying in WaitForMultipleObjects on ioAllowed, and
+	 * when signalled it writes all data in AsyncIO.ov and then sets ov.hEvent so that
+	 * ready_output gets triggered and (potentially) sends the reply to the port and
+	 * marks the port an non-busy.
+	 *
+	 * input:
+	 * The threaded_reader is lying waiting in ReadFile on the in fd and when a new
+	 * line is written it sets ov.hEvent that new data is available and then goes
+	 * and waits for ioAllowed to be set. ready_input is run when ov.hEvent is set and
+	 * delivers the data to the port. Then ioAllowed is signalled again and threaded_reader
+	 * goes back to ReadFile.
+	 *
+	 * shutdown:
+	 * In order to guarantee that all io is outputted before the driver is stopped,
+	 * fd_stop uses flushEvent and flushReplyEvent to make sure that there is no data
+	 * in ov which needs writing before returning from fd_stop.
+	 *
+	 **/
+
 	if (!create_file_thread(&dp->in, DO_READ)) {
 	    dp->port_num = PORT_FREE;
 	    return ERL_DRV_ERROR_GENERAL;
@@ -2241,6 +2310,8 @@ static void fd_stop(ErlDrvData d)
       (void) driver_select(dp->port_num,
 			   (ErlDrvEvent)dp->out.ov.hEvent,
 			   ERL_DRV_WRITE, 0);
+      SetEvent(dp->out.flushEvent);
+      WaitForSingleObject(dp->out.flushReplyEvent, INFINITE);
   }    
 
 }