From 7266f5ae68a0c9a63c7b99a85adc464906696449 Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Thu, 23 Jun 2016 22:56:18 +0200
Subject: [PATCH] Fix race condition when multiple threads write to
 MultiplexStream simultaneously

---
 panda/src/downloader/multiplexStreamBuf.cxx | 18 +++++-------------
 panda/src/downloader/multiplexStreamBuf.h   |  2 ++
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/panda/src/downloader/multiplexStreamBuf.cxx b/panda/src/downloader/multiplexStreamBuf.cxx
index e78eb1d838..daa2d78ed9 100644
--- a/panda/src/downloader/multiplexStreamBuf.cxx
+++ b/panda/src/downloader/multiplexStreamBuf.cxx
@@ -12,6 +12,7 @@
  */
 
 #include "multiplexStreamBuf.h"
+#include "lightMutexHolder.h"
 
 #if defined(WIN32_VC) || defined(WIN64_VC)
 #define WINDOWS_LEAN_AND_MEAN
@@ -113,10 +114,8 @@ void MultiplexStreamBuf::
 add_output(MultiplexStreamBuf::BufferType buffer_type,
            MultiplexStreamBuf::OutputType output_type,
            ostream *out, FILE *fout, bool owns_obj) {
-#ifdef OLD_HAVE_IPC
   // Ensure that we have the mutex while we fiddle with the list of outputs.
-  mutex_lock m(_lock);
-#endif
+  LightMutexHolder holder(_lock);
 
   Output o;
   o._buffer_type = buffer_type;
@@ -133,9 +132,7 @@ add_output(MultiplexStreamBuf::BufferType buffer_type,
  */
 void MultiplexStreamBuf::
 flush() {
-#ifdef OLD_HAVE_IPC
-  mutex_lock m(_lock);
-#endif
+  LightMutexHolder holder(_lock);
 
   write_chars("", 0, true);
 }
@@ -146,9 +143,7 @@ flush() {
  */
 int MultiplexStreamBuf::
 overflow(int ch) {
-#ifdef OLD_HAVE_IPC
-  mutex_lock m(_lock);
-#endif
+  LightMutexHolder holder(_lock);
 
   streamsize n = pptr() - pbase();
 
@@ -172,9 +167,7 @@ overflow(int ch) {
  */
 int MultiplexStreamBuf::
 sync() {
-#ifdef OLD_HAVE_IPC
-  mutex_lock m(_lock);
-#endif
+  LightMutexHolder holder(_lock);
 
   streamsize n = pptr() - pbase();
 
@@ -242,5 +235,4 @@ write_chars(const char *start, int length, bool flush) {
       break;
     }
   }
-
 }
diff --git a/panda/src/downloader/multiplexStreamBuf.h b/panda/src/downloader/multiplexStreamBuf.h
index e2d0f589b5..52a75c5ff9 100644
--- a/panda/src/downloader/multiplexStreamBuf.h
+++ b/panda/src/downloader/multiplexStreamBuf.h
@@ -17,6 +17,7 @@
 #include "pandabase.h"
 
 #include "pvector.h"
+#include "lightMutex.h"
 #include <stdio.h>
 
 /**
@@ -69,6 +70,7 @@ private:
   typedef pvector<Output> Outputs;
   Outputs _outputs;
 
+  LightMutex _lock;
   string _line_buffer;
 };