tevent: add tevent_cached_getpid() helper

This avoids a getpid() syscall per tevent_loop_once() iteration.

We provide tevent_cached_getpid() also as helper for external consumers
in order to have the logic only once.

Note the change to ABI/tevent-0.12.1.sigs will be reverted
with the bump to 0.13.0.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

5 files changed, 63 insertions, 9 deletions

diff --git a/lib/tevent/ABI/tevent-0.12.1.sigs b/lib/tevent/ABI/tevent-0.12.1.sigs
index 0e4d1e1fe26..68722a0e62f 100644
--- a/lib/tevent/ABI/tevent-0.12.1.sigs
+++ b/lib/tevent/ABI/tevent-0.12.1.sigs
@@ -22,6 +22,7 @@ _tevent_schedule_immediate: void (struct tevent_immediate *, struct tevent_conte
 _tevent_threaded_schedule_immediate: void (struct tevent_threaded_context *, struct tevent_immediate *, tevent_immediate_handler_t, void *, const char *, const char *)
 tevent_abort: void (struct tevent_context *, const char *)
 tevent_backend_list: const char **(TALLOC_CTX *)
+tevent_cached_getpid: pid_t (void)
 tevent_cleanup_pending_signal_handlers: void (struct tevent_signal *)
 tevent_common_add_fd: struct tevent_fd *(struct tevent_context *, TALLOC_CTX *, int, uint16_t, tevent_fd_handler_t, void *, const char *, const char *)
 tevent_common_add_signal: struct tevent_signal *(struct tevent_context *, TALLOC_CTX *, int, int, tevent_signal_handler_t, void *, const char *, const char *)
diff --git a/lib/tevent/tevent.c b/lib/tevent/tevent.c
index 81268a1bd7a..262fdaa22ed 100644
--- a/lib/tevent/tevent.c
+++ b/lib/tevent/tevent.c
@@ -199,6 +199,7 @@ static void tevent_common_wakeup_fini(struct tevent_context *ev);
 static pthread_mutex_t tevent_contexts_mutex = PTHREAD_MUTEX_INITIALIZER;
 static struct tevent_context *tevent_contexts = NULL;
 static pthread_once_t tevent_atfork_initialized = PTHREAD_ONCE_INIT;
+static pid_t tevent_cached_global_pid = 0;
 
 static void tevent_atfork_prepare(void)
 {
@@ -263,6 +264,8 @@ static void tevent_atfork_child(void)
 	struct tevent_context *ev;
 	int ret;
 
+	tevent_cached_global_pid = getpid();
+
 	for (ev = DLIST_TAIL(tevent_contexts); ev != NULL;
 	     ev = DLIST_PREV(ev)) {
 		struct tevent_threaded_context *tctx;
@@ -302,9 +305,41 @@ static void tevent_prep_atfork(void)
 	if (ret != 0) {
 		abort();
 	}
+
+	tevent_cached_global_pid = getpid();
+}
+
+#endif
+
+static int tevent_init_globals(void)
+{
+#ifdef HAVE_PTHREAD
+	int ret;
+
+	ret = pthread_once(&tevent_atfork_initialized, tevent_prep_atfork);
+	if (ret != 0) {
+		return ret;
+	}
+#endif
+
+	return 0;
 }
 
+_PUBLIC_ pid_t tevent_cached_getpid(void)
+{
+#ifdef HAVE_PTHREAD
+	tevent_init_globals();
+#ifdef TEVENT_VERIFY_CACHED_GETPID
+	if (tevent_cached_global_pid != getpid()) {
+		tevent_abort(NULL, "tevent_cached_global_pid invalid");
+	}
+#endif
+	if (tevent_cached_global_pid != 0) {
+		return tevent_cached_global_pid;
+	}
 #endif
+	return getpid();
+}
 
 int tevent_common_context_destructor(struct tevent_context *ev)
 {
@@ -434,13 +469,13 @@ static int tevent_common_context_constructor(struct tevent_context *ev)
 {
 	int ret;
 
-#ifdef HAVE_PTHREAD
-
-	ret = pthread_once(&tevent_atfork_initialized, tevent_prep_atfork);
+	ret = tevent_init_globals();
 	if (ret != 0) {
 		return ret;
 	}
 
+#ifdef HAVE_PTHREAD
+
 	ret = pthread_mutex_init(&ev->scheduled_mutex, NULL);
 	if (ret != 0) {
 		return ret;
diff --git a/lib/tevent/tevent.h b/lib/tevent/tevent.h
index 1c337adbf74..656df254be0 100644
--- a/lib/tevent/tevent.h
+++ b/lib/tevent/tevent.h
@@ -1909,6 +1909,22 @@ struct timeval tevent_timeval_add(const struct timeval *tv, uint32_t secs,
  */
 struct timeval tevent_timeval_current_ofs(uint32_t secs, uint32_t usecs);
 
+/**
+ *
+ * @brief A cached version of getpid()
+ *
+ * We use getpid() in a lot a performance critical situations
+ * in order to check if caches are still valid in the current process.
+ *
+ * Calling getpid() always add the cost of an additional syscall!
+ *
+ * When tevent is build with pthread support, we already make use
+ * of pthread_atfork(), so it's trivial to use it maintain a cache for getpid().
+ *
+ * @return              The pid of the current process.
+ */
+pid_t tevent_cached_getpid(void);
+
 /* @} */
 
 
diff --git a/lib/tevent/tevent_epoll.c b/lib/tevent/tevent_epoll.c
index 9cbe505c98a..1f1f47b2b21 100644
--- a/lib/tevent/tevent_epoll.c
+++ b/lib/tevent/tevent_epoll.c
@@ -206,7 +206,7 @@ static int epoll_init_ctx(struct epoll_event_context *epoll_ev)
 			     "Failed to set close-on-exec, file descriptor may be leaked to children.\n");
 	}
 
-	epoll_ev->pid = getpid();
+	epoll_ev->pid = tevent_cached_getpid();
 	talloc_set_destructor(epoll_ev, epoll_ctx_destructor);
 
 	return 0;
@@ -224,8 +224,9 @@ static void epoll_check_reopen(struct epoll_event_context *epoll_ev)
 	struct tevent_fd *fde;
 	bool *caller_panic_state = epoll_ev->panic_state;
 	bool panic_triggered = false;
+	pid_t pid = tevent_cached_getpid();
 
-	if (epoll_ev->pid == getpid()) {
+	if (epoll_ev->pid == pid) {
 		return;
 	}
 
@@ -241,7 +242,7 @@ static void epoll_check_reopen(struct epoll_event_context *epoll_ev)
 			     "Failed to set close-on-exec, file descriptor may be leaked to children.\n");
 	}
 
-	epoll_ev->pid = getpid();
+	epoll_ev->pid = pid;
 	epoll_ev->panic_state = &panic_triggered;
 	for (fde=epoll_ev->ev->fd_events;fde;fde=fde->next) {
 		fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT;
diff --git a/lib/tevent/tevent_port.c b/lib/tevent/tevent_port.c
index e91d442389d..ccb65a711b2 100644
--- a/lib/tevent/tevent_port.c
+++ b/lib/tevent/tevent_port.c
@@ -95,7 +95,7 @@ static int port_init_ctx(struct port_event_context *port_ev)
 			     "Failed to set close-on-exec, file descriptor may be leaked to children.\n");
 	}
 
-	port_ev->pid = getpid();
+	port_ev->pid = tevent_cached_getpid();
 	talloc_set_destructor(port_ev, port_ctx_destructor);
 
 	return 0;
@@ -199,8 +199,9 @@ static int port_update_event(struct port_event_context *port_ev, struct tevent_f
 static int port_check_reopen(struct port_event_context *port_ev)
 {
 	struct tevent_fd *fde;
+	pid_t pid = tevent_cached_getpid();
 
-	if (port_ev->pid == getpid()) {
+	if (port_ev->pid == pid) {
 		return 0;
 	}
 
@@ -217,7 +218,7 @@ static int port_check_reopen(struct port_event_context *port_ev)
 			     "Failed to set close-on-exec, file descriptor may be leaked to children.\n");
 	}
 
-	port_ev->pid = getpid();
+	port_ev->pid = pid;
 	for (fde=port_ev->ev->fd_events;fde;fde=fde->next) {
 		fde->additional_flags &= PORT_ADDITIONAL_FD_FLAG_HAS_ASSOCIATION;
 		if (port_update_event(port_ev, fde) != 0) {