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gmain: use Linux eventfd() for main context wake up
The Linux eventfd() call is basically tailor made for the main loop
wake up pipe - all we want is a threadsafe way to write to a file
descriptor, and wake up the context on the other end; we don't care
about the content at all.
The eventfd manual page basically explains the benefits:
Applications can use an eventfd file descriptor instead of a
pipe (see pipe(2)) in all cases where a pipe is used simply to
signal events. The kernel overhead of an eventfd file
descriptor is much lower than that of a pipe, and only one file
descriptor is required (versus the two required for a pipe).
When writing my multithreaded spawn test case I actually hit the 1024
file descriptor limit quickly, because we used 2 fds per main context.
This brings that down to 1.
https://bugzilla.gnome.org/show_bug.cgi?id=653140
This commit is contained in:
Colin Walters
parent
29bb7638a5
commit
3904c8761a
20
configure.ac
20
configure.ac
@ -2604,6 +2604,26 @@ main (void)
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AC_MSG_RESULT(no)
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])
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AC_MSG_CHECKING([for eventfd(2) system call])
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AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
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#include <sys/eventfd.h>
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#include <unistd.h>
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],[
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int
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main (void)
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{
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eventfd (0, EFD_CLOEXEC);
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return 0;
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}
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])],
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[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_EVENTFD, 1, [we have the eventfd(2) system call])
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],
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[
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AC_MSG_RESULT(no)
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])
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dnl ****************************************
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dnl *** GLib POLL* compatibility defines ***
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dnl ****************************************
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69
glib/gmain.c
69
glib/gmain.c
@ -49,6 +49,9 @@
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#ifdef G_OS_UNIX
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#include "glib-unix.h"
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#ifdef HAVE_EVENTFD
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#include <sys/eventfd.h>
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#endif
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#endif
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#include <signal.h>
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@ -397,6 +400,14 @@ static GSList *main_contexts_without_pipe = NULL;
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#ifndef G_OS_WIN32
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#ifdef HAVE_EVENTFD
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typedef struct {
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guint checked_eventfd : 1;
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guint have_eventfd : 1;
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} EventFdState;
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EventFdState event_fd_state = { 0, 0 };
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#endif
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/* The UNIX signal pipe contains a single byte specifying which
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* signal was received.
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*/
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@ -529,8 +540,10 @@ g_main_context_unref (GMainContext *context)
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if (g_thread_supported())
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{
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#ifndef G_OS_WIN32
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close (context->wake_up_pipe[0]);
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close (context->wake_up_pipe[1]);
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if (context->wake_up_pipe[0] != -1)
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close (context->wake_up_pipe[0]);
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if (context->wake_up_pipe[1] != -1)
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close (context->wake_up_pipe[1]);
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#else
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CloseHandle (context->wake_up_semaphore);
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#endif
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@ -556,8 +569,32 @@ g_main_context_init_pipe (GMainContext *context)
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if (context->wake_up_pipe[0] != -1)
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return;
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#ifdef HAVE_EVENTFD
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if (!event_fd_state.checked_eventfd
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|| event_fd_state.have_eventfd)
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{
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int efd;
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event_fd_state.checked_eventfd = TRUE;
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efd = eventfd (0, EFD_CLOEXEC);
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if (efd == -1 && errno == ENOSYS)
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{
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event_fd_state.have_eventfd = FALSE;
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if (!g_unix_open_pipe (context->wake_up_pipe, FD_CLOEXEC, &error))
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g_error ("Cannot create pipe main loop wake-up: %s", error->message);
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}
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else if (efd >= 0)
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{
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event_fd_state.have_eventfd = TRUE;
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context->wake_up_pipe[0] = efd;
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}
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else
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g_error ("Cannot create eventfd for main loop wake-up: %s", g_strerror (errno));
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}
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#else
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if (!g_unix_open_pipe (context->wake_up_pipe, FD_CLOEXEC, &error))
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g_error ("Cannot create pipe main loop wake-up: %s", error->message);
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#endif
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context->wake_up_rec.fd = context->wake_up_pipe[0];
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context->wake_up_rec.events = G_IO_IN;
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@ -580,7 +617,9 @@ g_main_context_init_pipe (GMainContext *context)
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void
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_g_main_thread_init (void)
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{
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GSList *curr = main_contexts_without_pipe;
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GSList *curr;
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curr = main_contexts_without_pipe;
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while (curr)
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{
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g_main_context_init_pipe ((GMainContext *)curr->data);
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@ -2942,8 +2981,18 @@ g_main_context_check (GMainContext *context,
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if (!context->poll_waiting)
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{
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#ifndef G_OS_WIN32
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gchar a;
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read (context->wake_up_pipe[0], &a, 1);
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#ifdef HAVE_EVENTFD
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if (event_fd_state.have_eventfd)
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{
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guint64 buf;
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read (context->wake_up_pipe[0], &buf, sizeof(guint64));
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}
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else
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#endif
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{
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gchar a;
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read (context->wake_up_pipe[0], &a, 1);
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}
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#endif
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}
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else
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@ -3794,7 +3843,15 @@ g_main_context_wakeup_unlocked (GMainContext *context)
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{
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context->poll_waiting = FALSE;
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#ifndef G_OS_WIN32
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write (context->wake_up_pipe[1], "A", 1);
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#ifdef HAVE_EVENTFD
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if (event_fd_state.have_eventfd)
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{
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guint64 buf = 1;
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write (context->wake_up_pipe[0], &buf, sizeof(buf));
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}
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else
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#endif
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write (context->wake_up_pipe[1], "A", 1);
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#else
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ReleaseSemaphore (context->wake_up_semaphore, 1, NULL);
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#endif
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