Log: Fix race in accessing the stream variable

Summary:
The code was attempting to copy the shared pointer member in order to
guarantee atomicity, but this is not enough. Instead, protect the
pointer with a proper read-write mutex.

This bug was present here for a long time, but my recent refactors must
have altered the timings slightly, such that now this fails fairly often
when running the tests: the test runner runs the "log disable" command
just as the thread monitoring the lldb-server child is about to report
that the server has exited.

I add a test case for this. It's not possible to reproduce the race
deterministically in normal circumstances, but I have verified that
before the fix, the test failed when run under tsan, and was running
fine afterwards.

Reviewers: clayborg, zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D30168

llvm-svn: 295712

1 files changed, 1 insertions, 1 deletions

diff --git a/lldb/source/Core/Log.cpp b/lldb/source/Core/Log.cpp
index 181dcc25bd7..874b879724d 100644
--- a/lldb/source/Core/Log.cpp
+++ b/lldb/source/Core/Log.cpp
@@ -400,7 +400,7 @@ void Log::WriteHeader(llvm::raw_ostream &OS, llvm::StringRef file,
 void Log::WriteMessage(const std::string &message) {
   // Make a copy of our stream shared pointer in case someone disables our
   // log while we are logging and releases the stream
-  auto stream_sp = m_stream_sp;
+  auto stream_sp = GetStream();
   if (!stream_sp)
     return;