ring buffer read : set read_from=-1 if read_from==write_to

2 files changed, 12 insertions, 4 deletions

diff --git a/lf_ring_buffer.c b/lf_ring_buffer.c
index 75b2f17..ad866e0 100644
--- a/lf_ring_buffer.c
+++ b/lf_ring_buffer.c
@@ -149,8 +149,15 @@ int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
             if (next==r->n_buf) next=0;
             /* will do bad things if data dst buffer is too small !! */
             memcpy( data, r->buffer[idx].data, LFRB_DATA_SIZE );
-            _LOG_( "write: CAS %d %d %d\n", r->read_from, idx, next );
-            if( CompareAndSwapInt( &r->read_from, idx, next ) ) break;
+            _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 */
+                    _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;
diff --git a/lf_ring_buffer_test.c b/lf_ring_buffer_test.c
index 348d202..e9e199a 100644
--- a/lf_ring_buffer_test.c
+++ b/lf_ring_buffer_test.c
@@ -6,8 +6,7 @@
 
 #include "lf_ring_buffer.h"
 
-//#define BUFFER_LEN 5000000
-#define BUFFER_LEN 500
+#define BUFFER_LEN 5000000
 
 static rb_data_t data[BUFFER_LEN][RB_DATA_LEN];
 
@@ -25,12 +24,14 @@ static void report( int n, uint64_t dt ) {
     fprintf(stdout,"%d operations in %d [ms] => %d [us] => %d [ns]\t >>> %d [ns/op]\n", n, (int)(dt/1000000), (int)(dt/1000), (int)dt, (int)(dt/n) );
 }
 
+/*
 static void feed_data( int n){
     int i;
     for(i=0; i<n; i++){
         sprintf(data[i],"hello world %04d\n",i);
     }
 }
+*/
 
 static uint64_t sequential_writes( lf_ring_buffer_t *ring, int n, int flags ) {
     int i;