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| author | Chris Darroch <chrisd@apache.org> | 2008-03-04 21:03:51 +0100 |
|---|---|---|
| committer | Chris Darroch <chrisd@apache.org> | 2008-03-04 21:03:51 +0100 |
| commit | 46ccf01ae7e1caadf26818afe2c212c9ccc8938d (patch) | |
| tree | dd7a34a3ec7a066b7852eda067a4efd9bb235476 /server/mpm/worker | |
| parent | Enable UAC transition from ApacheMonitor running as a vanilla user without priv (diff) | |
| download | apache2-46ccf01ae7e1caadf26818afe2c212c9ccc8938d.tar.xz apache2-46ccf01ae7e1caadf26818afe2c212c9ccc8938d.zip | |
add comment from event MPM's fdqueue ap_pop_pool() regarding
ABA problem and avoidance because only caller is single listener thread
git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@633612 13f79535-47bb-0310-9956-ffa450edef68
Diffstat (limited to 'server/mpm/worker')
| -rw-r--r-- | server/mpm/worker/fdqueue.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/server/mpm/worker/fdqueue.c b/server/mpm/worker/fdqueue.c index 8a75d24d1e..d46dd5361b 100644 --- a/server/mpm/worker/fdqueue.c +++ b/server/mpm/worker/fdqueue.c @@ -188,6 +188,14 @@ apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t *queue_info, apr_atomic_dec32(&(queue_info->idlers)); /* Atomically pop a pool from the recycled list */ + + /* This function is safe only as long as it is single threaded because + * it reaches into the queue and accesses "next" which can change. + * We are OK today because it is only called from the listener thread. + * cas-based pushes do not have the same limitation - any number can + * happen concurrently with a single cas-based pop. + */ + for (;;) { struct recycled_pool *first_pool = queue_info->recycled_pools; if (first_pool == NULL) { |