From f927efd77a8e75e330b3592996277ad6e6eb6a8d Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Thu, 25 Oct 2012 12:38:13 -0700
Subject: Add support for Linux eventfd(7) in the UNIX event loop

eventfd(7) uses less resources than a pipe, as it only needs to store a
single 64-bit integer, as opposed to a full buffer.

It was introduced first on Linux version 2.6.22 and glibc 2.7. However,
both the configure-time test and the runtime usage require the use of
EFD_CLOEXEC for thread-safety, so this code will be enabled only for
Linux 2.6.27 and up as well as glibc 2.9 and up.

Change-Id: Ic7e10b28d7b1d4ca24be614ed84055c4429a68e4
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
---
 src/corelib/kernel/qeventdispatcher_unix.cpp | 37 +++++++++++++++++++++++++---
 src/corelib/kernel/qeventdispatcher_unix_p.h |  3 +++
 2 files changed, 36 insertions(+), 4 deletions(-)

(limited to 'src')

diff --git a/src/corelib/kernel/qeventdispatcher_unix.cpp b/src/corelib/kernel/qeventdispatcher_unix.cpp
index 995f5101cb..6408147567 100644
--- a/src/corelib/kernel/qeventdispatcher_unix.cpp
+++ b/src/corelib/kernel/qeventdispatcher_unix.cpp
@@ -56,6 +56,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#ifndef QT_NO_EVENTFD
+#  include <sys/eventfd.h>
+#endif
+
 // VxWorks doesn't correctly set the _POSIX_... options
 #if defined(Q_OS_VXWORKS)
 #  if defined(_POSIX_MONOTONIC_CLOCK) && (_POSIX_MONOTONIC_CLOCK <= 0)
@@ -127,6 +131,12 @@ QEventDispatcherUNIXPrivate::QEventDispatcherUNIXPrivate()
         }
     }
 #else
+#  ifndef QT_NO_EVENTFD
+    thread_pipe[0] = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+    if (thread_pipe[0] != -1)
+        thread_pipe[1] = -1;
+    else // fall through the next "if"
+#  endif
     if (qt_safe_pipe(thread_pipe, O_NONBLOCK) == -1) {
         perror("QEventDispatcherUNIXPrivate(): Unable to create thread pipe");
         pipefail = true;
@@ -155,7 +165,8 @@ QEventDispatcherUNIXPrivate::~QEventDispatcherUNIXPrivate()
 #else
     // cleanup the common parts of the event loop
     close(thread_pipe[0]);
-    close(thread_pipe[1]);
+    if (thread_pipe[1] != -1)
+        close(thread_pipe[1]);
 #endif
 
     // cleanup timers
@@ -279,9 +290,18 @@ int QEventDispatcherUNIXPrivate::processThreadWakeUp(int nsel)
         ::read(thread_pipe[0], c, sizeof(c));
         ::ioctl(thread_pipe[0], FIOFLUSH, 0);
 #else
-        char c[16];
-        while (::read(thread_pipe[0], c, sizeof(c)) > 0)
-            ;
+#  ifndef QT_NO_EVENTFD
+        if (thread_pipe[1] == -1) {
+            // eventfd
+            eventfd_t value;
+            eventfd_read(thread_pipe[0], &value);
+        } else
+#  endif
+        {
+            char c[16];
+            while (::read(thread_pipe[0], c, sizeof(c)) > 0) {
+            }
+        }
 #endif
         if (!wakeUps.testAndSetRelease(1, 0)) {
             // hopefully, this is dead code
@@ -630,6 +650,15 @@ void QEventDispatcherUNIX::wakeUp()
 {
     Q_D(QEventDispatcherUNIX);
     if (d->wakeUps.testAndSetAcquire(0, 1)) {
+#ifndef QT_NO_EVENTFD
+        if (d->thread_pipe[1] == -1) {
+            // eventfd
+            eventfd_t value = 1;
+            int ret;
+            EINTR_LOOP(ret, eventfd_write(d->thread_pipe[0], value));
+            return;
+        }
+#endif
         char c = 0;
         qt_safe_write( d->thread_pipe[1], &c, 1 );
     }
diff --git a/src/corelib/kernel/qeventdispatcher_unix_p.h b/src/corelib/kernel/qeventdispatcher_unix_p.h
index 98ea19ced8..e96acf65af 100644
--- a/src/corelib/kernel/qeventdispatcher_unix_p.h
+++ b/src/corelib/kernel/qeventdispatcher_unix_p.h
@@ -148,6 +148,9 @@ public:
     virtual int processThreadWakeUp(int nsel);
 
     bool mainThread;
+
+    // note for eventfd(7) support:
+    // if thread_pipe[1] is -1, then eventfd(7) is in use and is stored in thread_pipe[0]
     int thread_pipe[2];
 
     // highest fd for all socket notifiers
-- 
cgit v1.2.3