use semaphore instead of futex

git-svn-id: http://ltt.polymtl.ca/svn@1627 04897980-b3bd-0310-b5e0-8ef037075253

diff --git a/usertrace-fast/ltt-usertrace-fast.c b/usertrace-fast/ltt-usertrace-fast.c
index d722460b10e1f4a98d4048feed7e46ea57b408c2..edc37b859ad94ac299a1ad5ec70c70ecc7f70e4c 100644 (file)
--- a/usertrace-fast/ltt-usertrace-fast.c
+++ b/usertrace-fast/ltt-usertrace-fast.c
@@ -319,14 +319,9 @@ static inline int ltt_buffer_put(struct ltt_buf *ltt_buf,
                 * It can also happen if this is a buffer we never got. */
                return -EIO;
        } else {
-               if(atomic_inc_return(&ltt_buf->writer_futex) <= 0) {
-                       atomic_set(&ltt_buf->writer_futex, 1);
-                       /* tell the client that buffer is now unfull */
-                       ret = futex((unsigned long)&ltt_buf->writer_futex,
-                                       FUTEX_WAKE, 1, 0, 0, 0);
-                       if(ret != 1) {
-                               dbg_printf("LTT warning : race condition : writer not waiting or too many writers\n");
-                       }
+               ret = sem_post(&ltt_buf->writer_sem);
+               if(ret < 0) {
+                       printf("error in sem_post");
                }
        }
 }
@@ -471,6 +466,10 @@ static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info,
 
        close(fd_process);
        
+       ret = sem_destroy(&shared_trace_info->channel.process.writer_sem);
+       if(ret < 0) {
+               perror("error in sem_destroy");
+       }
        munmap(shared_trace_info, sizeof(*shared_trace_info));
        
        exit(0);
@@ -501,9 +500,12 @@ void ltt_rw_init(void)
        shared_trace_info->nesting=0;
        memset(&shared_trace_info->channel.process, 0,
                        sizeof(shared_trace_info->channel.process));
-       /* Tricky semaphore : is in a shared memory space, so it's ok for a fast
-        * mutex (futex). */
-       atomic_set(&shared_trace_info->channel.process.writer_futex, LTT_N_SUBBUFS);
+       //Need NPTL!
+       ret = sem_init(&shared_trace_info->channel.process.writer_sem, 1,
+                                                                       LTT_N_SUBBUFS);
+       if(ret < 0) {
+               perror("error in sem_init");
+       }
        shared_trace_info->channel.process.alloc_size = LTT_BUF_SIZE_PROCESS;
        shared_trace_info->channel.process.subbuf_size = LTT_SUBBUF_SIZE_PROCESS;
        shared_trace_info->channel.process.start =

diff --git a/usertrace-fast/ltt/ltt-usertrace-fast.h b/usertrace-fast/ltt/ltt-usertrace-fast.h
index 77e0594ff58045c5c8fdb817c1656e95e74558d7..318eff6a0df7f29730addd11669cb2437e5c02e9 100644 (file)
--- a/usertrace-fast/ltt/ltt-usertrace-fast.h
+++ b/usertrace-fast/ltt/ltt-usertrace-fast.h
@@ -15,20 +15,12 @@
 #include <pthread.h>
 #include <stdint.h>
 #include <syscall.h>
-#include <linux/futex.h>
 #include <asm/timex.h>
+#include <semaphore.h>
 
 #include <ltt/ltt-facility-id-user_generic.h>
 #include <ltt/ltt-generic.h>
 
-#ifndef futex
-static inline __attribute__((no_instrument_function))
-       _syscall6(long, futex, unsigned long, uaddr, int, op, int, val,
-               unsigned long, timeout, unsigned long, uaddr2, int, val2)
-#endif //futex
-
-
-
 #ifndef        LTT_N_SUBBUFS
 #define LTT_N_SUBBUFS 2
 #endif //LTT_N_SUBBUFS
@@ -112,7 +104,7 @@ struct ltt_buf {
 
        atomic_t        events_lost;
        atomic_t        corrupted_subbuffers;
-       atomic_t        writer_futex;   /* futex on which the writer waits */
+       sem_t   writer_sem;     /* semaphore on which the writer waits */
        unsigned int    alloc_size;
        unsigned int    subbuf_size;
 };
@@ -418,19 +410,7 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
                                //if((SUBBUF_TRUNC(offset_begin, ltt_buf) 
                                //                              - SUBBUF_TRUNC(atomic_read(&ltt_buf->consumed), ltt_buf))
                                //                                      >= ltt_buf->alloc_size) {
-                                       if(atomic_dec_return(&ltt_buf->writer_futex) >= 0) {
-                                               /* non contended */
-                                       } else {
-                                               /* We block until the reader unblocks us */
-                                               atomic_set(&ltt_buf->writer_futex, -1);
-                                               /* We block until the reader tells us to wake up.
-                                                        Signals will simply cause this loop to restart.
-                                                        */
-                                               do {
-                                                       ret = futex((unsigned long)&ltt_buf->writer_futex,
-                                                                       FUTEX_WAIT, -1, 0, 0, 0);
-                                               } while(ret != 0 && ret != EWOULDBLOCK);
-                                       }
+                               sem_wait(&ltt_buf->writer_sem);
                                        /* go on with the write */
 
                                //} else {
@@ -440,6 +420,7 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
                        } else {
                                /* Next subbuffer corrupted. Force pushing reader even in normal
                                 * mode. It's safe to write in this new subbuffer. */
+                               sem_post(&ltt_buf->writer_sem);
                        }
                        size = ltt_get_header_size(trace, ltt_buf->start + offset_begin,
                                        before_hdr_pad, after_hdr_pad, header_size) + data_size;