Initialize the mutex in JNIEventsDiffAwareness

pthread mutexes must be initialized with pthread_mutex_init and cleaned
up with pthread_mutex_destroy.

This seems to fix a race where poll() would access invalid array indexes
on an array constructed based on the size of a shared list protected by
the mutex.  This is understandable because the mutex may not have been
doing anything due to the lack of its proper initialization -- and, if
so, I'm surprised the consequences were not more catastrophic.

As with any race condition, it is hard to confirm that this fixes the
observed problem, but I could trivially reproduce this issue earlier
and now I cannot with this fix after tens of runs.  See reproduction
code in the referenced bug for details on how to expose the issue.

Fixes #1676.

--
Change-Id: Ia5a4a8f12da7c3780f33266b9922eeba7645b3a4
Reviewed-on: https://cr.bazel.build/9230
PiperOrigin-RevId: 149414125
MOS_MIGRATED_REVID=149414125

1 files changed, 5 insertions, 1 deletions

diff --git a/src/main/native/fsevents.cc b/src/main/native/fsevents.cc
index b051580ee7..22f9d98152 100644
--- a/src/main/native/fsevents.cc
+++ b/src/main/native/fsevents.cc
@@ -32,6 +32,10 @@ struct JNIEventsDiffAwareness {
   // The former is called inside the FsEvents run loop and the latter
   // from Java threads.
   pthread_mutex_t mutex;
+
+  JNIEventsDiffAwareness() { pthread_mutex_init(&mutex, nullptr); }
+
+  ~JNIEventsDiffAwareness() { pthread_mutex_destroy(&mutex); }
 };
 
 // Callback called when an event is reported by the FSEvents API
@@ -64,7 +68,7 @@ Java_com_google_devtools_build_lib_skyframe_MacOSXFsEventsDiffAwareness_create(
     JNIEnv *env, jobject fsEventsDiffAwareness, jobjectArray paths,
     jdouble latency) {
   // Create a FSEventStreamContext to pass around (env, fsEventsDiffAwareness)
-  JNIEventsDiffAwareness *info = new JNIEventsDiffAwareness;
+  JNIEventsDiffAwareness *info = new JNIEventsDiffAwareness();
 
   FSEventStreamContext context;
   context.version = 0;