Windows: flush shell notifications when dismounting with /q (#1852)

* Windows: flush shell notifications when dismounting with /q

* Windows: limit the /q notification flush to the command line dismount

ProcessExitsAfterCommand was set while parsing /q and stayed set when
the process went on as the background task (/q background, and
/q preferences, which is also used at logon). Later interactive
dismounts, automatic dismounts through DismountAll and the hotkeys then
flushed as well, which would also delay the cache wipe that the force
dismount and wipe hotkeys issue after DismountAll.

Set the flag only for the dismount requested on the command line and
clear it right after, whatever Silent is. Rename it to
FlushDriveRemovalNotifications, as /q doesn't necessarily end the
process.

Reword the comments: according to the documentation, SHCNF_FLUSH makes
SHChangeNotify return once the notification has been delivered, which
doesn't mean that Explorer has finished updating its display, and the
cause of the reported ghost drive letters hasn't been established.

Author: amail80

src/Common/Dlgcode.c

@@ -162,6 +162,10 @@ HWND MainDlg = NULL;
 wchar_t *lpszTitle = NULL;
 
 BOOL Silent = FALSE;
+/* Set by Mount.c only while it carries out a dismount requested on the command line
+   with /q. UnmountVolumeBase and DismountAll then send the drive removal notification
+   again with SHCNF_FLUSH, as they do when Silent is set. */
+BOOL FlushDriveRemovalNotifications = FALSE;
 BOOL bPreserveTimestamp = TRUE;
 BOOL bShowDisconnectedNetworkDrives = FALSE;
 BOOL bHideWaitingDialog = FALSE;
@@ -9826,13 +9830,13 @@ static BOOL UnmountVolumeBase (HWND hwndDlg, int nDosDriveNo, BOOL forceUnmount,
 
 	BroadcastDeviceChange (DBT_DEVICEREMOVECOMPLETE, nDosDriveNo, 0);
 
-	/* GH #337, GH #1426: When running in silent/CLI mode, the process may
-	   exit immediately after unmount. BroadcastDeviceChange sends
-	   SHChangeNotify asynchronously, so Explorer may not process the drive
-	   removal before the process exits, leaving a ghost drive letter.
-	   Re-send the notification with SHCNF_FLUSH to force synchronous
-	   processing by Explorer before we return. */
-	if (Silent && !DeviceChangeBroadcastDisabled)
+	/* GH #337, GH #1426: ghost drive letters were reported after dismounts
+	   requested on the command line; their cause hasn't been established.
+	   When Silent or FlushDriveRemovalNotifications is set, the notification
+	   is sent again with SHCNF_FLUSH. According to the documentation,
+	   SHChangeNotify then returns only once it has been delivered, which
+	   doesn't mean that Explorer has finished updating its display. */
+	if ((Silent || FlushDriveRemovalNotifications) && !DeviceChangeBroadcastDisabled)
 	{
 		wchar_t root[] = { (wchar_t) (nDosDriveNo + L'A'), L':', L'\\', 0 };
 		SHChangeNotify (SHCNE_DRIVEREMOVED, SHCNF_PATH | SHCNF_FLUSH, root, NULL);

src/Common/Dlgcode.h

@@ -133,6 +133,7 @@ extern int ScreenDPI;
 extern double DlgAspectRatio;
 extern HWND MainDlg;
 extern BOOL Silent;
+extern BOOL FlushDriveRemovalNotifications;
 extern BOOL bHistory;
 extern BOOL bPreserveTimestamp;
 extern BOOL bShowDisconnectedNetworkDrives;

src/Mount/Mount.c

@@ -6351,10 +6351,9 @@ static BOOL DismountAll (HWND hwndDlg, BOOL forceUnmount, BOOL interact, int dis
 	if (removedDrives)
 		BroadcastDeviceChange (DBT_DEVICEREMOVECOMPLETE, 0, removedDrives);
 
-	/* GH #337, GH #1426: Flush shell notifications synchronously in
-	   silent/CLI mode to prevent ghost drive letters when the process
-	   exits immediately after dismount. */
-	if (Silent && !DeviceChangeBroadcastDisabled)
+	/* GH #337, GH #1426: as in UnmountVolumeBase, send the notifications again
+	   with SHCNF_FLUSH when Silent or FlushDriveRemovalNotifications is set. */
+	if ((Silent || FlushDriveRemovalNotifications) && !DeviceChangeBroadcastDisabled)
 	{
 		for (i = 0; i < 26; i++)
 		{
@@ -8446,6 +8445,10 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 			}
 
 			// Dismount
+			/* With /q, flush the drive removal notifications of this dismount even
+			   without /s (see UnmountVolumeBase). Only for this request: a process
+			   that goes on as the background task doesn't flush later dismounts. */
+			FlushDriveRemovalNotifications = Quit;
 			if (cmdUnmountDrive >= 0)
 			{
 				MOUNT_LIST_STRUCT mountList;
@@ -8467,6 +8470,7 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 				if (!DismountAll (hwndDlg, bForceUnmount, !Silent, UNMOUNT_MAX_AUTO_RETRIES, UNMOUNT_AUTO_RETRY_DELAY))
 					exitCode = 1;
 			}
+			FlushDriveRemovalNotifications = FALSE;
 
 			// TaskBar icon
 			if (bEnableBkgTask)