first lock free ring buffer implementation

1 files changed, 125 insertions, 0 deletions

diff --git a/lf_ring_buffer.c b/lf_ring_buffer.c
new file mode 100644
index 0000000..7796206
--- /dev/null
+++ b/lf_ring_buffer.c
@@ -0,0 +1,125 @@
+/*
+ * File     : lf_ring_buffer.h
+ * Author   : Jérémy Zurcher  <jeremy@asynk.ch>
+ * Date     : 05/01/010
+ * License  :
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining
+ *  a copy of this software and associated documentation files (the
+ *  "Software"), to deal in the Software without restriction, including
+ *  without limitation the rights to use, copy, modify, merge, publish,
+ *  distribute, sublicense, and/or sell copies of the Software, and to
+ *  permit persons to whom the Software is furnished to do so, subject to
+ *  the following conditions:
+ *  
+ *  The above copyright notice and this permission notice shall be
+ *  included in all copies or substantial portions of the Software.
+ *  
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#include "lf_ring_buffer.h"
+#include "lf_portable_cas.h"
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+/* initialize an empty lf_ring_buffer struct */
+lf_ring_buffer_t* lf_ring_buffer_create( int n_buf ) {
+    /* alloc ring_buffer struct */
+    lf_ring_buffer_t *r = malloc(sizeof(lf_ring_buffer_t));
+    if(r==NULL) return NULL;
+    /* */
+    r->buffer = malloc(sizeof(lf_buffer_el_t)*n_buf);
+    if(r->buffer==NULL) {
+        free(r);
+        return NULL;
+    }
+    memset(r->buffer,0,sizeof(lf_buffer_el_t)*r->n_buf);
+    r->n_buf = n_buf;
+    r->read_from = -1;
+    r->write_to = 0;
+    r->write_delay=BACKOFF_DELAY_INIT;
+    return r;
+}
+
+/* destroy an lf_ring_buffer strcture */
+void lf_ring_buffer_destroy( lf_ring_buffer_t *r ) {
+    free(r->buffer);
+    free(r);
+}
+
+/* write data into the ring buffer */
+int lf_ring_buffer_write( lf_ring_buffer_t *r, rb_data_t *data, int flags ) {
+    int idx;
+    int next;
+    struct timespec st;
+    st.tv_sec=0;
+    /* reserve a buffer */
+    for(;;){
+        idx = r->write_to;
+        if(IS_AVAILABLE(idx) ) {
+            /* 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) {
+                next = (idx+1)%r->n_buf;
+                /* 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
+                */
+                if( CompareAndSwapInt( &r->write_to, idx, next ) ) break;
+            }
+            /* TODO simply reloop, nothing to do ??? */
+        } else {
+            if(IS_NOT_BLOCKING(flags)) return -1;
+            st.tv_nsec=r->write_delay;
+            nanosleep(&st,NULL);
+            if(r->write_delay<BACKOFF_DELAY_MAX) r->write_delay+=BACKOFF_DELAY_INC;
+        }
+    }
+    /* 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, RB_DATA_SIZE*sizeof(rb_data_t) );
+    MARK_AS_FILLED( idx );
+    if(r->write_delay>BACKOFF_DELAY_INIT) r->write_delay-=BACKOFF_DELAY_INC;
+    return 0;
+}
+
+/* read data from the ring buffer */
+int lf_ring_buffer_read( lf_ring_buffer_t *r, rb_data_t *data, int flags ) {
+    int idx;
+    struct timespec st;
+    st.tv_sec=0;
+    if(r->read_from==-1) return -1;
+    for(;;) {
+        idx = r->read_from;
+        if(!IS_AVAILABLE(idx)) {
+            memcpy( data, r->buffer[idx].data, RB_DATA_SIZE*sizeof(rb_data_t) );
+            if( CompareAndSwapInt( &r->read_from, idx, (idx+1)%r->n_buf ) ) break;
+        } else { 
+            if(IS_NOT_BLOCKING(flags)) return -1;
+            st.tv_nsec=r->read_delay;
+            nanosleep(&st,NULL);
+            if(r->read_delay<BACKOFF_DELAY_MAX) r->read_delay+=BACKOFF_DELAY_INC;
+        }
+    }
+    /* finish the read process */
+    MARK_AS_READ( idx );
+    if(r->read_delay>BACKOFF_DELAY_INIT) r->read_delay-=BACKOFF_DELAY_INC;
+    return 0;
+}
+