Do init_profile_extras constructor tasks only once

Bug: http://b/116873221

Currently, every coverage-enabled binary (the main executable or shared
library) in the process executes the init_profile_extras constructor
leading to redundant initialization.

Instead, add a weak global value that gets set once so following
constructors don't set a signal handler or create a pthread.  It's ok to
do this before the constructor succeeds because if pthread creation or
signal handler registration failed once, they are unlikely to succeed
the second time.

This is thread-safe since constructor initialization is single-threaded.
The one possibility for a race - the process doesn't have any
coverage-enabled library, and multiple threads dlopen() coverage-enabled
shared libraries - seems quite unlikely.

Test: Verify that only one extra thread is created for a daemon (adbd).
Change-Id: Ie969311c2ddac147497c870b5c365b4617b3c60a
Merged-In: Ie969311c2ddac147497c870b5c365b4617b3c60a
(cherry picked from commit e76c23dc6b7bff0c7404744b9bdde0d02465acdf)

1 files changed, 6 insertions, 0 deletions

diff --git a/toolchain-extras/profile-extras.cpp b/toolchain-extras/profile-extras.cpp
index 2d685084..f999a6b2 100644
--- a/toolchain-extras/profile-extras.cpp
+++ b/toolchain-extras/profile-extras.cpp
@@ -67,6 +67,8 @@ void *property_watch_loop(__unused void *arg) {
   }
 }
 
+__attribute__((weak)) int init_profile_extras_once = 0;
+
 // Initialize libprofile-extras:
 // - Install a signal handler that triggers __gcov_flush on <GCOV_FLUSH_SIGNAL>.
 // - Create a thread that calls __gcov_flush when <kCoveragePropName> sysprop
@@ -81,6 +83,10 @@ void *property_watch_loop(__unused void *arg) {
 // We force the linker to include init_profile_extras() by passing
 // '-uinit_profile_extras' to the linker (in build/soong).
 __attribute__((constructor)) int init_profile_extras(void) {
+  if (init_profile_extras_once)
+    return 0;
+  init_profile_extras_once = 1;
+
   sighandler_t ret1 = signal(GCOV_FLUSH_SIGNAL, gcov_signal_handler);
   if (ret1 == SIG_ERR) {
     return -1;