diff options
| -rw-r--r-- | lf_ring_buffer.c | 40 |
1 files changed, 21 insertions, 19 deletions
diff --git a/lf_ring_buffer.c b/lf_ring_buffer.c index 70074bc..606e29a 100644 --- a/lf_ring_buffer.c +++ b/lf_ring_buffer.c @@ -83,25 +83,26 @@ int lf_ring_buffer_empty( lf_ring_buffer_t *r ) { return r->read_from==-1; } /* write data into the ring buffer */ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) { - int idx, next; + int write_to, read_from, next; struct timespec backoff; int backoff_time = BACKOFF_NANO_SLEEP; /* reserve a buffer */ for(;;){ - idx = r->write_to; - if(LFRB_IS_AVAILABLE( r->buffer[idx] ) ) { - /* read_from==idx means that the buffer is full and that a writer thread which at first reserved this buffer + write_to = r->write_to; + read_from = r->read_from; + if(LFRB_IS_AVAILABLE( r->buffer[write_to] ) ) { + /* read_from==write_to 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 ) { - next = idx+1; + if( read_from!=write_to ) { + next = write_to+1; if (next==r->n_buf) next=0; /* what might have happend between IS_AVAILABLE and now : * - a writter has reserved this buffer => write_to has moved => CAS fails * - a reader has consumed a buffer => read_from has moved => we've got more space */ - _LOG_CAS_( "write: CAS %d %d %d\n", r->write_to, idx, next ); - if( CompareAndSwapInt( &r->write_to, idx, next ) ) { + _LOG_CAS_( "write: CAS %d %d %d\n", r->write_to, write_to, next ); + if( CompareAndSwapInt( &r->write_to, write_to, next ) ) { /* !!!!!!!!!!!!!! WARNING !!!!!!!!!!!!!!!!! * - if the ring is empty before this write operation (r->read_from==-1 or latest idx) * - and n_buf other threads execute this same function before the next CAS is finished @@ -110,7 +111,7 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) { * - 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 ); + if(r->read_from==-1) CompareAndSwapInt( &r->read_from, -1, write_to ); break; } } else { @@ -130,25 +131,26 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) { backoff_time += BACKOFF_NANO_SLEEP; } /* fill this buffer and mark it as filled */ - memcpy( LFRB_DATA_PTR(r->buffer[idx]), data, LFRB_DATA_SIZE ); - LFRB_MARK_AS_FILLED( r->buffer[idx] ); + memcpy( LFRB_DATA_PTR(r->buffer[write_to]), data, LFRB_DATA_SIZE ); + LFRB_MARK_AS_FILLED( r->buffer[write_to] ); return 0; } /* read data from the ring buffer */ int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) { - int idx, next; + int write_to, read_from, next; struct timespec backoff; int backoff_time = BACKOFF_NANO_SLEEP; for(;;) { - idx = r->read_from; - if( !(LFRB_IS_AVAILABLE( r->buffer[idx] )) && r->read_from!=-1 ) { - next = idx+1; + write_to = r->write_to; + read_from = r->read_from; + if( !(LFRB_IS_AVAILABLE( r->buffer[read_from] )) && read_from!=-1 ) { + next = read_from+1; if (next==r->n_buf) next=0; /* will do bad things if data dst buffer is too small !! */ - memcpy( data, LFRB_DATA_PTR(r->buffer[idx]), LFRB_DATA_SIZE ); - _LOG_CAS_( "read: CAS %d %d %d\n", r->read_from, idx, next ); - if( CompareAndSwapInt( &r->read_from, idx, next ) ) { + memcpy( data, LFRB_DATA_PTR(r->buffer[read_from]), LFRB_DATA_SIZE ); + _LOG_CAS_( "read: CAS %d %d %d\n", r->read_from, read_from, next ); + if( CompareAndSwapInt( &r->read_from, read_from, next ) ) { if(r->read_from==r->write_to) { /* the buffer is empty but writers will see it as full */ _LOG_CAS_( "read: empty CAS %d %d %d\n", r->read_from, next, -1 ); @@ -166,7 +168,7 @@ int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) { backoff_time += BACKOFF_NANO_SLEEP; } /* finish the read process */ - LFRB_MARK_AS_READ( r->buffer[idx] ); + LFRB_MARK_AS_READ( r->buffer[read_from] ); return 0; } |