path: root/src/process
diff options
authorRich Felker <>2014-07-05 23:29:55 -0400
committerRich Felker <>2014-07-05 23:29:55 -0400
commit83dc6eb087633abcf5608ad651d3b525ca2ec35e (patch)
tree1bed298fdfcf4167d63fed54d055a3c66af4f0f0 /src/process
parent4c48501ee2a022a0dd207a2db4d346a00f9927a1 (diff)
eliminate use of cached pid from thread structure
the main motivation for this change is to remove the assumption that the tid of the main thread is also the pid of the process. (the value returned by the set_tid_address syscall was used to fill both fields despite it semantically being the tid.) this is historically and presently true on linux and unlikely to change, but it conceivably could be false on other systems that otherwise reproduce the linux syscall api/abi. only a few parts of the code were actually still using the cached pid. in a couple places (aio and synccall) it was a minor optimization to avoid a syscall. caching could be reintroduced, but lazily as part of the public getpid function rather than at program startup, if it's deemed important for performance later. in other places (cancellation and pthread_kill) the pid was completely unnecessary; the tkill syscall can be used instead of tgkill. this is actually a rather subtle issue, since tgkill is supposedly a solution to race conditions that can affect use of tkill. however, as documented in the commit message for commit 7779dbd2663269b465951189b4f43e70839bc073, tgkill does not actually solve this race; it just limits it to happening within one process rather than between processes. we use a lock that avoids the race in pthread_kill, and the use in the cancellation signal handler is self-targeted and thus not subject to tid reuse races, so both are safe regardless of which syscall (tgkill or tkill) is used.
Diffstat (limited to 'src/process')
1 files changed, 1 insertions, 1 deletions
diff --git a/src/process/fork.c b/src/process/fork.c
index f8cf21e7..43c52bc4 100644
--- a/src/process/fork.c
+++ b/src/process/fork.c
@@ -24,7 +24,7 @@ pid_t fork(void)
if (libc.has_thread_pointer && !ret) {
pthread_t self = __pthread_self();
- self->tid = self->pid = __syscall(SYS_getpid);
+ self->tid = __syscall(SYS_gettid);
memset(&self->robust_list, 0, sizeof self->robust_list);
libc.threads_minus_1 = 0;