signal fix, take 2

git-svn-id: http://ltt.polymtl.ca/svn@2355 04897980-b3bd-0310-b5e0-8ef037075253

diff --git a/ltt-usertrace/ltt/ltt-usertrace-fast.h b/ltt-usertrace/ltt/ltt-usertrace-fast.h
index 7c295e4b38f932d9692214220a1244738556fce9..536362fbd786c75eec4b66ea2a4da89e42c825d2 100644 (file)
--- a/ltt-usertrace/ltt/ltt-usertrace-fast.h
+++ b/ltt-usertrace/ltt/ltt-usertrace-fast.h
@@ -368,15 +368,6 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
        int ret;
        sigset_t oldset, set;
 
-       /* sem_wait is not signal safe. Disable signals around it. */
-
-       /* Disable signals */
-       ret = sigfillset(&set);
-       if(ret) perror("LTT Error in sigfillset\n"); 
-       
-       ret = pthread_sigmask(SIG_BLOCK, &set, &oldset);
-       if(ret) perror("LTT Error in pthread_sigmask\n");
-
        do {
                offset_old = atomic_read(&ltt_buf->offset);
                offset_begin = offset_old;
@@ -416,16 +407,26 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
                                                                                                                                                                                                                                 ltt_buf)])
                                - atomic_read(&ltt_buf->commit_count[SUBBUF_INDEX(offset_begin,
                                                                                                                                                                                 ltt_buf)]);
+
                        if(reserve_commit_diff == 0) {
                                /* Next buffer not corrupted. */
                                //if((SUBBUF_TRUNC(offset_begin, ltt_buf) 
                                //                              - SUBBUF_TRUNC(atomic_read(&ltt_buf->consumed), ltt_buf))
                                //                                      >= ltt_buf->alloc_size) {
                                {
+                                       /* sem_wait is not signal safe. Disable signals around it.
+                                        * Signals are kept disabled to make sure we win the cmpxchg. */
+
+                                       /* Disable signals */
+                                       ret = sigfillset(&set);
+                                       if(ret) perror("LTT Error in sigfillset\n"); 
+       
+                                       ret = pthread_sigmask(SIG_BLOCK, &set, &oldset);
+                                       if(ret) perror("LTT Error in pthread_sigmask\n");
+
                                        sem_wait(&ltt_buf->writer_sem);
 
                                }
-
                                        /* go on with the write */
 
                                //} else {
@@ -435,7 +436,8 @@ 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);
+                               /* No sem_post is required because we fall through without doing a
+                                * sem_wait. */
                        }
                        size = ltt_get_header_size(trace, ltt_buf->start + offset_begin,
                                        before_hdr_pad, after_hdr_pad, header_size) + data_size;
@@ -443,6 +445,10 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
                                /* Event too big for subbuffers, report error, don't complete 
                                 * the sub-buffer switch. */
                                atomic_inc(&ltt_buf->events_lost);
+                               if(reserve_commit_diff == 0) {
+                                       ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
+                                       if(ret) perror("LTT Error in pthread_sigmask\n");
+                               }
                                return NULL;
                        } else {
                                /* We just made a successful buffer switch and the event fits in the
@@ -463,10 +469,6 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
        } while(atomic_cmpxchg(&ltt_buf->offset, offset_old, offset_end)
                                                        != offset_old);
 
-       /* Enable signals */
-       ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
-       if(ret) perror("LTT Error in pthread_sigmask\n");
-
        /* Push the reader if necessary */
        do {
                consumed_old = atomic_read(&ltt_buf->consumed);
@@ -541,6 +543,14 @@ static inline void * __attribute__((no_instrument_function)) ltt_reserve_slot(
        }
 
        if(begin_switch) {
+               /* Enable signals : this is what guaranteed that same reserve which did the
+                * sem_wait does in fact win the cmpxchg for the offset. We only call
+                * these system calls on buffer boundaries because of their performance
+                * cost. */
+               if(reserve_commit_diff == 0) {
+                       ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
+                       if(ret) perror("LTT Error in pthread_sigmask\n");
+               }
                /* New sub-buffer */
                /* This code can be executed unordered : writers may already have written
                         to the sub-buffer before this code gets executed, caution. */