Use Linux eventfd() if kernel supports it

git-svn-id: file:///home/lennart/svn/public/pulseaudio/branches/lennart@1908 fefdeb5f-60dc-0310-8127-8f9354f1896f

src/pulsecore/fdsem.c

@@ -25,6 +25,7 @@
 #include <config.h>
 #endif
 
+#include <sys/syscall.h>
 #include <unistd.h>
 #include <errno.h>
 
@@ -35,10 +36,37 @@
 #include <pulsecore/core-util.h>
 #include <pulse/xmalloc.h>
 
+#ifdef __linux__
+
+#if !defined(__NR_eventfd) && defined(__i386__)
+#define __NR_eventfd 323
+#endif
+
+#if !defined(__NR_eventfd) && defined(__x86_64__)
+#define __NR_eventfd 284
+#endif
+
+#if !defined(SYS_eventfd) && defined(__NR_eventfd)
+#define SYS_eventfd __NR_eventfd
+#endif
+
+#ifdef SYS_eventfd
+#define HAVE_EVENTFD
+
+static inline long eventfd(unsigned count) {
+    return syscall(SYS_eventfd, count);
+}
+
+#endif
+#endif
+
 #include "fdsem.h"
 
 struct pa_fdsem {
     int fds[2];
+#ifdef HAVE_EVENTFD
+    int efd;
+#endif
     pa_atomic_t waiting;
     pa_atomic_t signalled;
     pa_atomic_t in_pipe;
@@ -48,25 +76,38 @@ pa_fdsem *pa_fdsem_new(void) {
     pa_fdsem *f;
 
     f = pa_xnew(pa_fdsem, 1);
-    
-    if (pipe(f->fds) < 0) {
-        pa_xfree(f);
-        return NULL;
-    }
 
-    pa_make_fd_cloexec(f->fds[0]);
-    pa_make_fd_cloexec(f->fds[1]);
+#ifdef HAVE_EVENTFD
+    if ((f->efd = eventfd(0)) >= 0) {
+        pa_make_fd_cloexec(f->efd);
+        f->fds[0] = f->fds[1] = -1;
+
+    } else
+#endif
+    {
+        if (pipe(f->fds) < 0) {
+            pa_xfree(f);
+            return NULL;
+        }
+
+        pa_make_fd_cloexec(f->fds[0]);
+        pa_make_fd_cloexec(f->fds[1]);
+    }
 
     pa_atomic_store(&f->waiting, 0);
     pa_atomic_store(&f->signalled, 0);
     pa_atomic_store(&f->in_pipe, 0);
-    
+
     return f;
 }
 
 void pa_fdsem_free(pa_fdsem *f) {
     pa_assert(f);
 
+#ifdef HAVE_EVENTFD
+    if (f->efd >= 0)
+        pa_close(f->efd);
+#endif
     pa_close_pipe(f->fds);
 
     pa_xfree(f);
@@ -81,12 +122,24 @@ static void flush(pa_fdsem *f) {
 
     do {
         char x[10];
-        
+
+#ifdef HAVE_EVENTFD
+        if (f->efd >= 0) {
+            uint64_t u;
+
+            if ((r = read(f->efd, &u, sizeof(u))) != sizeof(u)) {
+                pa_assert(r < 0 && errno == EINTR);
+                continue;
+            }
+            r = (ssize_t) u;
+        } else
+#endif
+
         if ((r = read(f->fds[0], &x, sizeof(x))) <= 0) {
             pa_assert(r < 0 && errno == EINTR);
             continue;
         }
-        
+
     } while (pa_atomic_sub(&f->in_pipe, r) > r);
 }
 
@@ -98,11 +151,22 @@ void pa_fdsem_post(pa_fdsem *f) {
         if (pa_atomic_load(&f->waiting)) {
             ssize_t r;
             char x = 'x';
-            
+
             pa_atomic_inc(&f->in_pipe);
 
             for (;;) {
-                
+
+#ifdef HAVE_EVENTFD
+                if (f->efd >= 0) {
+                    uint64_t u = 1;
+
+                    if ((r = write(f->efd, &u, sizeof(u))) != sizeof(u)) {
+                        pa_assert(r < 0 && errno == EINTR);
+                        continue;
+                    }
+                } else
+#endif
+
                 if ((r = write(f->fds[1], &x, 1)) != 1) {
                     pa_assert(r < 0 && errno == EINTR);
                     continue;
@@ -123,16 +187,29 @@ void pa_fdsem_wait(pa_fdsem *f) {
         return;
 
     pa_atomic_inc(&f->waiting);
-        
+
     while (!pa_atomic_cmpxchg(&f->signalled, 1, 0)) {
         char x[10];
         ssize_t r;
-        
+
+#ifdef HAVE_EVENTFD
+        if (f->efd >= 0) {
+            uint64_t u;
+
+            if ((r = read(f->efd, &u, sizeof(u))) != sizeof(u)) {
+                pa_assert(r < 0 && errno == EINTR);
+                continue;
+            }
+
+            r = (ssize_t) u;
+        } else
+#endif
+
         if ((r = read(f->fds[0], &x, sizeof(x))) <= 0) {
             pa_assert(r < 0 && errno == EINTR);
             continue;
         }
-            
+
         pa_atomic_sub(&f->in_pipe, r);
     }
 
@@ -143,17 +220,21 @@ int pa_fdsem_try(pa_fdsem *f) {
     pa_assert(f);
 
     flush(f);
-    
+
     if (pa_atomic_cmpxchg(&f->signalled, 1, 0))
         return 1;
 
     return 0;
 }
 
-
 int pa_fdsem_get(pa_fdsem *f) {
     pa_assert(f);
-    
+
+#ifdef HAVE_EVENTFD
+    if (f->efd >= 0)
+        return f->efd;
+#endif
+
     return f->fds[0];
 }
 
@@ -170,7 +251,7 @@ int pa_fdsem_before_poll(pa_fdsem *f) {
     if (pa_atomic_cmpxchg(&f->signalled, 1, 0)) {
         pa_assert_se(pa_atomic_dec(&f->waiting) >= 1);
         return -1;
-    }        
+    }
     return 0;
 }