[pulseaudio-discuss] [PATCH] core: Remember pa_write() type in pa_fdsem_post()

[Peter Meerwald]

From: Peter Meerwald <p.meerwald at bct-electronic.com>

pa_write() knows two types of operation:
calling send() and calling write()

there is a flag (a pointer to an int) passed to pa_write()
which can remember which write type was successful

if the pointer is NULL or the int is 0, send() is tried first,
with a fallback to write() if send() resulted in ENOTSOCK

pa_fdsem_post() calls pa_write() with a NULL pointer;
unfortunately (at least with HAVE_SYS_EVENTFD_H #define'd) send()
always fails here and write() is called -- causing an extra syscall
quite frequently

strace:
send(17, "\1\0\0\0\0\0\0\0", 8, MSG_NOSIGNAL) = -1 ENOTSOCK (Socket operation on non-socket)
write(17, "\1\0\0\0\0\0\0\0", 8) = 8

the patch adds a write_type field to pa_fdsem to the successful
pa_write() type can be remembered and unnecessary send() calls are
avoided

Signed-off-by: Peter Meerwald <p.meerwald at bct-electronic.com>
---
 src/pulsecore/fdsem.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/pulsecore/fdsem.c b/src/pulsecore/fdsem.c
index 14fcbd6..1d3d44a 100644
--- a/src/pulsecore/fdsem.c
+++ b/src/pulsecore/fdsem.c
@@ -52,7 +52,7 @@ struct pa_fdsem {
 #ifdef HAVE_SYS_EVENTFD_H
     int efd;
 #endif
-
+    int write_type;
     pa_fdsem_data *data;
 };
 
@@ -196,7 +196,7 @@ void pa_fdsem_post(pa_fdsem *f) {
                 if (f->efd >= 0) {
                     uint64_t u = 1;
 
-                    if ((r = pa_write(f->efd, &u, sizeof(u), NULL)) != sizeof(u)) {
+                    if ((r = pa_write(f->efd, &u, sizeof(u), &f->write_type)) != sizeof(u)) {
                         if (r >= 0 || errno != EINTR) {
                             pa_log_error("Invalid write to eventfd: %s", r < 0 ? pa_cstrerror(errno) : "EOF");
                             pa_assert_not_reached();
@@ -207,7 +207,7 @@ void pa_fdsem_post(pa_fdsem *f) {
                 } else
 #endif
 
-                if ((r = pa_write(f->fds[1], &x, 1, NULL)) != 1) {
+                if ((r = pa_write(f->fds[1], &x, 1, &f->write_type)) != 1) {
                     if (r >= 0 || errno != EINTR) {
                         pa_log_error("Invalid write to pipe: %s", r < 0 ? pa_cstrerror(errno) : "EOF");
                         pa_assert_not_reached();
-- 
1.7.9.5