From 5ccc756c560bdf6e17886b903574848e514008d7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Camilla=20L=C3=B6wy?= Date: Fri, 18 Feb 2022 14:29:43 +0100 Subject: [PATCH] X11: Fix empty event race condition with a pipe There is a seemingly unavoidable race condition when waiting for data on the X11 display connection, as long as any other thread is also making Xlib calls. The event data we are waiting for could be read by the other thread as part of looking for the reply to its request, before our poll has begun. This commit replaces the X11 event sent by glfwPostEmptyEvent with writing to an unnamed pipe. The race condition remains if other Xlib calls are made on other threads, but glfwPostEmptyEvent should now be race-free. This commit is based on work by pcwalton, OlivierSohn, kovidgoyal and joaodasilva. Closes #2033 Related to #379 Related to #1281 Related to #1285 (cherry picked from commit cd22e2849512a88d0ab77bc7a3458646625f2c50) --- CONTRIBUTORS.md | 2 ++ README.md | 2 ++ docs/news.dox | 6 ++++++ src/x11_init.c | 43 +++++++++++++++++++++++++++++++++++++++++++ src/x11_platform.h | 1 + src/x11_window.c | 44 +++++++++++++++++++++++++++++++++++--------- 6 files changed, 89 insertions(+), 9 deletions(-) diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md index b35d2428..c17b7374 100644 --- a/CONTRIBUTORS.md +++ b/CONTRIBUTORS.md @@ -180,12 +180,14 @@ video tutorials. - Ali Sherief - Yoshiki Shibukawa - Dmitri Shuralyov + - Joao da Silva - Daniel Sieger - Daniel Skorupski - Bradley Smith - Cliff Smolinsky - Patrick Snape - Erlend Sogge Heggen + - Olivier Sohn - Julian Squires - Johannes Stein - Pontus Stenetorp diff --git a/README.md b/README.md index 6e150414..f0c1ac02 100644 --- a/README.md +++ b/README.md @@ -129,6 +129,8 @@ information on what to include when reporting a bug. (#2024) - [X11] Bugfix: Joystick events could lead to busy-waiting (#1872) - [X11] Bugfix: `glfwWaitEvents*` did not continue for joystick events + - [X11] Bugfix: `glfwPostEmptyEvent` could be ignored due to race condition + (#379,#1281,#1285,#2033) - [Wayland] Added support for key names via xkbcommon - [Wayland] Bugfix: Key repeat could lead to a race condition (#1710) - [Wayland] Bugfix: Activating a window would emit two input focus events diff --git a/docs/news.dox b/docs/news.dox index c21a8b8a..b5421c1a 100644 --- a/docs/news.dox +++ b/docs/news.dox @@ -306,6 +306,12 @@ GLFW_TRANSPARENT_FRAMEBUFFER on Windows 7 if DWM transparency is off (the Transparency setting under Personalization > Window Color). +@subsubsection emptyevents_33 Empty events on X11 no longer roundtrip to server + +Starting with GLFW 3.3.7, events posted with @ref glfwPostEmptyEvent now use a separate +unnamed pipe instead of sending an X11 client event to the helper window. + + @subsection deprecations_33 Deprecations in version 3.3 @subsubsection charmods_callback_33 Character with modifiers callback diff --git a/src/x11_init.c b/src/x11_init.c index 3bf8b839..5e6071f5 100644 --- a/src/x11_init.c +++ b/src/x11_init.c @@ -36,6 +36,9 @@ #include #include #include +#include +#include +#include // Translate the X11 KeySyms for a key to a GLFW key code @@ -968,6 +971,37 @@ static Window createHelperWindow(void) CWEventMask, &wa); } +// Create the pipe for empty events without assumuing the OS has pipe2(2) +// +static GLFWbool createEmptyEventPipe(void) +{ + if (pipe(_glfw.x11.emptyEventPipe) != 0) + { + _glfwInputError(GLFW_PLATFORM_ERROR, + "X11: Failed to create empty event pipe: %s", + strerror(errno)); + return GLFW_FALSE; + } + + for (int i = 0; i < 2; i++) + { + const int sf = fcntl(_glfw.x11.emptyEventPipe[i], F_GETFL, 0); + const int df = fcntl(_glfw.x11.emptyEventPipe[i], F_GETFD, 0); + + if (sf == -1 || df == -1 || + fcntl(_glfw.x11.emptyEventPipe[i], F_SETFL, sf | O_NONBLOCK) == -1 || + fcntl(_glfw.x11.emptyEventPipe[i], F_SETFD, df | FD_CLOEXEC) == -1) + { + _glfwInputError(GLFW_PLATFORM_ERROR, + "X11: Failed to set flags for empty event pipe: %s", + strerror(errno)); + return GLFW_FALSE; + } + } + + return GLFW_TRUE; +} + // X error handler // static int errorHandler(Display *display, XErrorEvent* event) @@ -1089,6 +1123,9 @@ int _glfwPlatformInit(void) getSystemContentScale(&_glfw.x11.contentScaleX, &_glfw.x11.contentScaleY); + if (!createEmptyEventPipe()) + return GLFW_FALSE; + if (!initExtensions()) return GLFW_FALSE; @@ -1206,6 +1243,12 @@ void _glfwPlatformTerminate(void) #if defined(__linux__) _glfwTerminateJoysticksLinux(); #endif + + if (_glfw.x11.emptyEventPipe[0] || _glfw.x11.emptyEventPipe[1]) + { + close(_glfw.x11.emptyEventPipe[0]); + close(_glfw.x11.emptyEventPipe[1]); + } } const char* _glfwPlatformGetVersionString(void) diff --git a/src/x11_platform.h b/src/x11_platform.h index 37946a29..30c73a88 100644 --- a/src/x11_platform.h +++ b/src/x11_platform.h @@ -238,6 +238,7 @@ typedef struct _GLFWlibraryX11 double restoreCursorPosX, restoreCursorPosY; // The window whose disabled cursor mode is active _GLFWwindow* disabledCursorWindow; + int emptyEventPipe[2]; // Window manager atoms Atom NET_SUPPORTED; diff --git a/src/x11_window.c b/src/x11_window.c index 6de0bcd4..9f08fc6d 100644 --- a/src/x11_window.c +++ b/src/x11_window.c @@ -114,8 +114,12 @@ static GLFWbool waitForX11Event(double* timeout) // static GLFWbool waitForAnyEvent(double* timeout) { - nfds_t count = 1; - struct pollfd fds[2] = { { ConnectionNumber(_glfw.x11.display), POLLIN } }; + nfds_t count = 2; + struct pollfd fds[3] = + { + { ConnectionNumber(_glfw.x11.display), POLLIN }, + { _glfw.x11.emptyEventPipe[0], POLLIN } + }; #if defined(__linux__) if (_glfw.linjs.inotify > 0) @@ -137,6 +141,32 @@ static GLFWbool waitForAnyEvent(double* timeout) return GLFW_TRUE; } +// Writes a byte to the empty event pipe +// +static void writeEmptyEvent(void) +{ + for (;;) + { + const char byte = 0; + const int result = write(_glfw.x11.emptyEventPipe[1], &byte, 1); + if (result == 1 || (result == -1 && errno != EINTR)) + break; + } +} + +// Drains available data from the empty event pipe +// +static void drainEmptyEvents(void) +{ + for (;;) + { + char dummy[64]; + const int result = read(_glfw.x11.emptyEventPipe[0], dummy, sizeof(dummy)); + if (result == -1 && errno != EINTR) + break; + } +} + // Waits until a VisibilityNotify event arrives for the specified window or the // timeout period elapses (ICCCM section 4.2.2) // @@ -2782,6 +2812,8 @@ GLFWbool _glfwPlatformRawMouseMotionSupported(void) void _glfwPlatformPollEvents(void) { + drainEmptyEvents(); + #if defined(__linux__) _glfwDetectJoystickConnectionLinux(); #endif @@ -2826,13 +2858,7 @@ void _glfwPlatformWaitEventsTimeout(double timeout) void _glfwPlatformPostEmptyEvent(void) { - XEvent event = { ClientMessage }; - event.xclient.window = _glfw.x11.helperWindowHandle; - event.xclient.format = 32; // Data is 32-bit longs - event.xclient.message_type = _glfw.x11.NULL_; - - XSendEvent(_glfw.x11.display, _glfw.x11.helperWindowHandle, False, 0, &event); - XFlush(_glfw.x11.display); + writeEmptyEvent(); } void _glfwPlatformGetCursorPos(_GLFWwindow* window, double* xpos, double* ypos)