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authorVolker Lendecke <vl@samba.org>2010-02-16 12:22:08 +0100
committerVolker Lendecke <vl@samba.org>2010-02-16 13:21:10 +0100
commit725b3654f831fbe0388cc09f46269903c9eef1d7 (patch)
tree0935e8d4d3246292bcf7cd4b1453bebb23e4f3a8
parent07978bd175395e0dc770f68fff5b8bd8b0fdeb51 (diff)
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s3: Avoid a thundering herd in g_lock_unlock
Only notify the first 5 pending lock waiters. This avoids a thundering herd problem that is really nasty in a cluster. It also makes acquiring a lock a bit more FIFO, lock waiters are added to the end of the array.
-rw-r--r--source3/lib/g_lock.c17
1 files changed, 16 insertions, 1 deletions
diff --git a/source3/lib/g_lock.c b/source3/lib/g_lock.c
index e2620255d9..512c0680d9 100644
--- a/source3/lib/g_lock.c
+++ b/source3/lib/g_lock.c
@@ -530,13 +530,23 @@ static NTSTATUS g_lock_force_unlock(struct g_lock_ctx *ctx, const char *name,
}
if ((lock_type & G_LOCK_PENDING) == 0) {
+ int num_wakeups = 0;
+
/*
- * We've been the lock holder. Tell all others to retry.
+ * We've been the lock holder. Others to retry. Don't
+ * tell all others to avoid a thundering herd. In case
+ * this leads to a complete stall because we miss some
+ * processes, the loop in g_lock_lock tries at least
+ * once a minute.
*/
+
for (i=0; i<num_locks; i++) {
if ((locks[i].lock_type & G_LOCK_PENDING) == 0) {
continue;
}
+ if (!process_exists(locks[i].pid)) {
+ continue;
+ }
/*
* Ping all waiters to retry
@@ -549,6 +559,11 @@ static NTSTATUS g_lock_force_unlock(struct g_lock_ctx *ctx, const char *name,
procid_str(talloc_tos(),
&locks[i].pid),
nt_errstr(status)));
+ } else {
+ num_wakeups += 1;
+ }
+ if (num_wakeups > 5) {
+ break;
}
}
}