Changeset 9414abc in mainline for uspace/lib/c/generic/fibril_synch.c

Timestamp:

2010-11-06T09:58:51Z (13 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

1712f87, 32efd86

Parents:

55bd76c

Message:

Add deadlock detection for cases when the rwlock is owned by only one reader.
Associate the rwlock ownership with the first reader so that the detection works
at least partially even if the lock is owned by multiple readers. The ownership
information is not passed onto the remaining readers when the owner unlocks the
lock.

File:

• uspace/lib/c/generic/fibril_synch.c (modified) (4 diffs)

uspace/lib/c/generic/fibril_synch.c

@@ -180 +180 @@
 void fibril_rwlock_read_lock(fibril_rwlock_t *frw)
 {
+        fibril_t *f = (fibril_t *) fibril_get_id();
+        
         futex_down(&async_futex);
         if (frw->writers) {
-                fibril_t *f = (fibril_t *) fibril_get_id();
                 awaiter_t wdata;
 
@@ -195 +196 @@
                 fibril_switch(FIBRIL_TO_MANAGER);
         } else {
-                frw->readers++;
+                /* Consider the first reader the owner. */
+                if (frw->readers++ == 0)
+                        frw->oi.owned_by = f;
                 futex_up(&async_futex);
         }
@@ -229 +232 @@
         assert(frw->readers || (frw->writers == 1));
         if (frw->readers) {
-                if (--frw->readers)
+                if (--frw->readers) {
+                        if (frw->oi.owned_by == (fibril_t *) fibril_get_id()) {
+                                /*
+                                 * If this reader firbril was considered the
+                                 * owner of this rwlock, clear the ownership
+                                 * information even if there are still more
+                                 * readers.
+                                 *
+                                 * This is the limitation of the detection
+                                 * mechanism rooted in the fact that tracking
+                                 * all readers would require dynamically
+                                 * allocated memory for keeping linkage info.
+                                 */
+                                frw->oi.owned_by = NULL;
+                        }
                         goto out;
+                }
         } else {
                 frw->writers--;
@@ -265 +283 @@
                         list_remove(&wdp->wu_event.link);
                         fibril_add_ready(wdp->fid);
-                        frw->readers++;
+                        if (frw->readers++ == 0) {
+                                /* Consider the first reader the owner. */
+                                frw->oi.owned_by = f;
+                        }
                         optimize_execution_power();
                 }