[lttng-dev] [RFC PATCH lttng-ust] Add tracepoint_disable_destructors()

[Mathieu Desnoyers]

Calling this function from an instrumented program allows disabling
tracepoint destructors. This allows threads to continue calling
tracepoint code even after the tracepoint destructors have run. This is
needed for applications that exit without joining all their threads.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
CC: Jeffrey Chen <cpthk at live.com>
---
 include/lttng/tracepoint.h | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index 16348b8..bcd8d67 100644
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -227,6 +227,21 @@ struct lttng_ust_tracepoint_dlopen {
 
 extern struct lttng_ust_tracepoint_dlopen tracepoint_dlopen;
 
+/* Disable tracepoint destructors. */
+int __tracepoints__disable_destructors __attribute__((weak));
+
+/*
+ * Programs that have threads that survive after they exit, and
+ * therefore call library destructors, should disable the tracepoint
+ * destructors by calling tracepoint_disable_destructors(). This will
+ * leak the tracepoint instrumentation library shared object, leaving
+ * its teardown to the operating system process teardown.
+ */
+static inline void tracepoint_disable_destructors(void)
+{
+	__tracepoints__disable_destructors = 1;
+}
+
 #if defined(TRACEPOINT_DEFINE) || defined(TRACEPOINT_CREATE_PROBES)
 
 /*
@@ -299,7 +314,7 @@ __tracepoints__destroy(void)
 {
 	int ret;
 
-	if (--__tracepoint_registered)
+	if (--__tracepoint_registered || __tracepoints__disable_destructors)
 		return;
 	if (tracepoint_dlopen.liblttngust_handle && !__tracepoint_ptrs_registered) {
 		ret = dlclose(tracepoint_dlopen.liblttngust_handle);
@@ -402,7 +417,7 @@ __tracepoints__ptrs_destroy(void)
 {
 	int ret;
 
-	if (--__tracepoint_ptrs_registered)
+	if (--__tracepoint_ptrs_registered || __tracepoints__disable_destructors)
 		return;
 	if (tracepoint_dlopen.tracepoint_unregister_lib)
 		tracepoint_dlopen.tracepoint_unregister_lib(__start___tracepoints_ptrs);
-- 
2.1.4