diff options
| -rw-r--r-- | lf_ring_buffer.c | 48 |
1 files 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] ); |