From 301cce4248a48512b87431509f406d59728ac886 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9my=20Zurcher?= <jeremy@asynk.ch>
Date: Fri, 8 Jan 2010 08:44:19 +0100
Subject: some optimizations and cleanups
---
lf_ring_buffer.c | 48 ++++++++++++++++++++++++++----------------------
1 file changed, 26 insertions(+), 22 deletions(-)
diff --git a/lf_ring_buffer.c b/lf_ring_buffer.c
index 506b0af..79edcff 100644
--- a/lf_ring_buffer.c
+++ b/lf_ring_buffer.c
@@ -99,7 +99,7 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
/* read_from==idx means that the buffer is full and that a writer thread which at first reserved this buffer
* hasn't had enough CPU cycles to call MARK_AS_FILLED
*/
- if(!(r->read_from==idx)) {
+ if( r->read_from!=idx ) {
next = idx+1;
if (next==r->n_buf) next=0;
/* what might have happend between IS_AVAILABLE and now :
@@ -107,27 +107,33 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
* - a reader has consumed a buffer => read_from has moved => we've got more space
*/
_LOG_( "write: CAS %d %d %d\n", r->write_to, idx, next );
- if( CompareAndSwapInt( &r->write_to, idx, next ) ) break;
+ if( CompareAndSwapInt( &r->write_to, idx, next ) ) {
+ /* !!!!!!!!!!!!!! WARNING !!!!!!!!!!!!!!!!!
+ * - if the ring is empty before this write operation (r->read_from==-1 or latest idx)
+ * - and n_buf other threads call this same function before this point
+ * then, the last thread will :
+ * - see this buffer as available
+ * - and see the ring as empty instead of full !!!!!
+ * so it will ends with two threads writing on this buffer
+ */
+ if(r->read_from==-1) CompareAndSwapInt( &r->read_from, -1, idx );
+ break;
+ }
} else {
- /* TODO simply reloop, nothing to do ??? */
- // TODO ERROR when all has been read
- _LOG_("write: buffer full %d %d\n",r->read_from,idx);
+ _LOG_("write: ring full %d %d\n",r->read_from,idx);
+ if(IS_NOT_BLOCKING(flags)) return -1;
+ backoff.tv_sec = 0;
+ backoff.tv_nsec = BACKOFF_NANO_SLEEP;
+ nanosleep(&backoff,NULL);
}
} else {
- _LOG_("write: not available\n");
+ _LOG_("write: buffer not available\n");
if(IS_NOT_BLOCKING(flags)) return -1;
backoff.tv_sec = 0;
backoff.tv_nsec = BACKOFF_NANO_SLEEP;
nanosleep(&backoff,NULL);
}
}
- /* try to set read_from on idx if it has not been initialized yet
- * !!!!!!!!!!!!!! WARNING !!!!!!!!!!!!!!!!!
- * there is a really tiny chance if the ring is too small and there is a lot of writers that,
- * another thread might have reserved this same buffer before this
- * which means this thread and the other will write data to this current buffer !!!!
- */
- if(r->read_from==-1) CompareAndSwapInt( &r->read_from, -1, idx );
/* fill this buffer and mark it as filled */
memcpy( r->buffer[idx].data, data, LFRB_DATA_SIZE );
LFRB_MARK_AS_FILLED( r->buffer[idx] );
@@ -138,10 +144,9 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
int idx, next;
struct timespec backoff;
- if(r->read_from==-1) return -1;
for(;;) {
idx = r->read_from;
- if( !(LFRB_IS_AVAILABLE( r->buffer[idx] )) ) {
+ if( !(LFRB_IS_AVAILABLE( r->buffer[idx] )) && r->read_from!=-1 ) {
next = idx+1;
if (next==r->n_buf) next=0;
/* will do bad things if data dst buffer is too small !! */
@@ -149,19 +154,18 @@ int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
_LOG_( "read: CAS %d %d %d\n", r->read_from, idx, next );
if( CompareAndSwapInt( &r->read_from, idx, next ) ) {
if(r->read_from==r->write_to) {
- /* the buffer is actually empty but writers will see it as full */
+ /* the buffer is empty but writers will see it as full */
_LOG_( "read: empty CAS %d %d %d\n", r->read_from, next, -1 );
CompareAndSwapInt( &r->read_from, next, -1 );
}
break;
}
- } else {
- _LOG_("read: not available\n");
- if(IS_NOT_BLOCKING(flags)) return -1;
- backoff.tv_sec = 0;
- backoff.tv_nsec = BACKOFF_NANO_SLEEP;
- nanosleep(&backoff,NULL);
}
+ _LOG_("read: ring empty\n");
+ if(IS_NOT_BLOCKING(flags)) return -1;
+ backoff.tv_sec = 0;
+ backoff.tv_nsec = BACKOFF_NANO_SLEEP;
+ nanosleep(&backoff,NULL);
}
/* finish the read process */
LFRB_MARK_AS_READ( r->buffer[idx] );
--
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