From b1fe837b8ea3b42ab062ed1856d7bed53d5a2473 Mon Sep 17 00:00:00 2001
From: frosch <frosch@openttd.org>
Date: Sat, 11 Mar 2017 13:05:54 +0000
Subject: (svn r27775) -Fix [FS#6510]: Insufficient thread synchronisation when
 switching blitters. (JGR)

---
 src/gfxinit.cpp            |  9 ++++++++-
 src/video/sdl_v.cpp        | 11 +++++++++--
 src/video/sdl_v.h          |  4 ++++
 src/video/video_driver.hpp | 13 +++++++++++++
 src/video/win32_v.cpp      | 11 +++++++++--
 src/video/win32_v.h        |  4 ++++
 6 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/src/gfxinit.cpp b/src/gfxinit.cpp
index 6dea627dd..06534ad29 100644
--- a/src/gfxinit.cpp
+++ b/src/gfxinit.cpp
@@ -290,6 +290,8 @@ static bool SwitchNewGRFBlitter()
 	const bool animation_wanted = HasBit(_display_opt, DO_FULL_ANIMATION);
 	const char *cur_blitter = BlitterFactory::GetCurrentBlitter()->GetName();
 
+	VideoDriver::GetInstance()->AcquireBlitterLock();
+
 	for (uint i = 0; i < lengthof(replacement_blitters); i++) {
 		if (animation_wanted && (replacement_blitters[i].animation == 0)) continue;
 		if (!animation_wanted && (replacement_blitters[i].animation == 1)) continue;
@@ -298,7 +300,10 @@ static bool SwitchNewGRFBlitter()
 		if (!IsInsideMM(depth_wanted_by_grf, replacement_blitters[i].min_grf_depth, replacement_blitters[i].max_grf_depth + 1)) continue;
 		const char *repl_blitter = replacement_blitters[i].name;
 
-		if (strcmp(repl_blitter, cur_blitter) == 0) return false;
+		if (strcmp(repl_blitter, cur_blitter) == 0) {
+			VideoDriver::GetInstance()->ReleaseBlitterLock();
+			return false;
+		}
 		if (BlitterFactory::GetBlitterFactory(repl_blitter) == NULL) continue;
 
 		DEBUG(misc, 1, "Switching blitter from '%s' to '%s'... ", cur_blitter, repl_blitter);
@@ -313,6 +318,8 @@ static bool SwitchNewGRFBlitter()
 		if (BlitterFactory::SelectBlitter(cur_blitter) == NULL || !VideoDriver::GetInstance()->AfterBlitterChange()) usererror("Failed to reinitialize video driver. Specify a fixed blitter in the config");
 	}
 
+	VideoDriver::GetInstance()->ReleaseBlitterLock();
+
 	return true;
 }
 
diff --git a/src/video/sdl_v.cpp b/src/video/sdl_v.cpp
index 4bb44c9d7..3668f8602 100644
--- a/src/video/sdl_v.cpp
+++ b/src/video/sdl_v.cpp
@@ -817,11 +817,18 @@ bool VideoDriver_SDL::ToggleFullscreen(bool fullscreen)
 }
 
 bool VideoDriver_SDL::AfterBlitterChange()
+{
+	return CreateMainSurface(_screen.width, _screen.height);
+}
+
+void VideoDriver_SDL::AcquireBlitterLock()
 {
 	if (_draw_mutex != NULL) _draw_mutex->BeginCritical(true);
-	bool ret = CreateMainSurface(_screen.width, _screen.height);
+}
+
+void VideoDriver_SDL::ReleaseBlitterLock()
+{
 	if (_draw_mutex != NULL) _draw_mutex->EndCritical(true);
-	return ret;
 }
 
 #endif /* WITH_SDL */
diff --git a/src/video/sdl_v.h b/src/video/sdl_v.h
index 730f82b93..8855c3566 100644
--- a/src/video/sdl_v.h
+++ b/src/video/sdl_v.h
@@ -31,6 +31,10 @@ public:
 
 	/* virtual */ bool AfterBlitterChange();
 
+	/* virtual */ void AcquireBlitterLock();
+
+	/* virtual */ void ReleaseBlitterLock();
+
 	/* virtual */ bool ClaimMousePointer();
 
 	/* virtual */ const char *GetName() const { return "sdl"; }
diff --git a/src/video/video_driver.hpp b/src/video/video_driver.hpp
index 916044d35..5cb3c6cc3 100644
--- a/src/video/video_driver.hpp
+++ b/src/video/video_driver.hpp
@@ -49,6 +49,7 @@ public:
 
 	/**
 	 * Callback invoked after the blitter was changed.
+	 * This may only be called between AcquireBlitterLock and ReleaseBlitterLock.
 	 * @return True if no error.
 	 */
 	virtual bool AfterBlitterChange()
@@ -56,6 +57,18 @@ public:
 		return true;
 	}
 
+	/**
+	 * Acquire any lock(s) required to be held when changing blitters.
+	 * These lock(s) may not be acquired recursively.
+	 */
+	virtual void AcquireBlitterLock() { }
+
+	/**
+	 * Release any lock(s) required to be held when changing blitters.
+	 * These lock(s) may not be acquired recursively.
+	 */
+	virtual void ReleaseBlitterLock() { }
+
 	virtual bool ClaimMousePointer()
 	{
 		return true;
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
index c37ebd7dd..e536ae8e5 100644
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -1333,11 +1333,18 @@ bool VideoDriver_Win32::ToggleFullscreen(bool full_screen)
 }
 
 bool VideoDriver_Win32::AfterBlitterChange()
+{
+	return AllocateDibSection(_screen.width, _screen.height, true) && this->MakeWindow(_fullscreen);
+}
+
+void VideoDriver_Win32::AcquireBlitterLock()
 {
 	if (_draw_mutex != NULL) _draw_mutex->BeginCritical(true);
-	bool ret = AllocateDibSection(_screen.width, _screen.height, true) && this->MakeWindow(_fullscreen);
+}
+
+void VideoDriver_Win32::ReleaseBlitterLock()
+{
 	if (_draw_mutex != NULL) _draw_mutex->EndCritical(true);
-	return ret;
 }
 
 void VideoDriver_Win32::EditBoxLostFocus()
diff --git a/src/video/win32_v.h b/src/video/win32_v.h
index 21d59185b..7609d0422 100644
--- a/src/video/win32_v.h
+++ b/src/video/win32_v.h
@@ -31,6 +31,10 @@ public:
 
 	/* virtual */ bool AfterBlitterChange();
 
+	/* virtual */ void AcquireBlitterLock();
+
+	/* virtual */ void ReleaseBlitterLock();
+
 	/* virtual */ bool ClaimMousePointer();
 
 	/* virtual */ void EditBoxLostFocus();
-- 
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