luo980/libuv
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

unix: speed up uv_async_send() some more

Browse Source 
Use atomic compare-and-swap to detect if we've been preempted by another thread
and therefore can avoid making the expensive write() syscall.

Speeds up the heavily contended case by about 1-2% and has little if any impact
on the non-contended case. I wasn't able to measure the difference at any rate.
This commit is contained in:
Ben Noordhuis 2012-07-02 04:27:22 +02:00
parent a2204abc8e
commit 3d9c1ebfeb
1 changed files with 11 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
src/unix/async.c
View File

@ -53,7 +53,17 @@ int uv_async_send(uv_async_t* handle) {
if (handle->pending)
return 0;
handle->pending = 1; /* XXX needs a memory barrier? */
/* Micro-optimization: use atomic compare-and-swap to detect if we've been
* preempted by another thread and don't have to make an expensive syscall.
* This speeds up the heavily contended case by about 1-2% and has little
* if any impact on the non-contended case.
*/
#if __GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 1 /* gcc >= 4.1 */
if (__sync_val_compare_and_swap(&handle->pending, 0, 1))
return 0;
#else
handle->pending = 1;
#endif
do
r = write(handle->loop->async_pipefd[1], "x", 1);