add reserve, tsc and alignment atomicity with cmpxchg : add memory barrier to protect.

git-svn-id: http://ltt.polymtl.ca/svn@1001 04897980-b3bd-0310-b5e0-8ef037075253

diff --git a/genevent/genevent.c b/genevent/genevent.c
index 5930489f755bc1f7f9ce7140f31313509a337c85..62db1274f173941dd20ff4065b0127f0e58a1283 100644 (file)
--- a/genevent/genevent.c
+++ b/genevent/genevent.c
@@ -540,8 +540,12 @@ void generateStructFunc(FILE * fp, char * facName, unsigned long checksum){
                 * address for alignment */
                /* NOTE : using cmpxchg in reserve with repeat for atomicity */
     // Replaces _offset
+               /* NOTE2 : as the read old address from memory must come before any
+                * protected event, let's add a memory barrier() to make sure the compiler
+                * will not reorder this read. */
                fprintf(fp, "\t\tdo {\n");
                fprintf(fp, "\t\t\told_address = buf->data + buf->offset;\n");
+               fprintf(fp, "\t\t\tbarrier();\n");
     fprintf(fp, "\t\t\tchar *ptr = (char*)old_address;\n");
 
 
@@ -602,7 +606,12 @@ void generateStructFunc(FILE * fp, char * facName, unsigned long checksum){
 
     fprintf(fp, "\t\t\tevent_length = (unsigned long)ptr -"
                                "(unsigned long)old_address;\n");
-
+               
+               /* let's put some protection before the cmpxchg : the space reservation and
+                * the get TSC are not dependant from each other. I don't want the compiler
+                * to reorder those in the wrong order. And relay_reserve is inline, so
+                * _yes_, the compiler could mess it up. */
+               fprintf(fp, "\t\t\tbarrier();\n");
                fprintf(fp, "\t\t\tbuff = relay_reserve(channel->rchan, event_length, "
                                                                                                "old_address);\n");
                fprintf(fp, "\n");