Unittest for thread_wrapper.

Added an explanation of the state variables of posix, wrote a simple test.
This might help in fixing the TSAN issue with thread.

BUG=webrtc:300
TEST=

Review URL: https://webrtc-codereview.appspot.com/583008

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2270 4adac7df-926f-26a2-2b94-8c16560cd09d

src/system_wrappers/source/system_wrappers.gyp

@@ -193,6 +193,7 @@
             'data_log_helpers_unittest.cc',
             'data_log_c_helpers_unittest.c',
             'data_log_c_helpers_unittest.h',
+            'thread_unittest.cc',
             'trace_unittest.cc',
           ],
           'conditions': [

src/system_wrappers/source/thread_posix.cc

@@ -8,6 +8,40 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+// The state of a thread is controlled by the two member variables
+// _alive and _dead.
+// _alive represents the state the thread has been ordered to achieve.
+// It is set to true by the thread at startup, and is set to false by
+// other threads, using SetNotAlive() and Stop().
+// _dead represents the state the thread has achieved.
+// It is written by the thread encapsulated by this class only
+// (except at init). It is read only by the Stop() method.
+// The Run() method fires _event when it's started; this ensures that the
+// Start() method does not continue until after _dead is false.
+// This protects against premature Stop() calls from the creator thread, but
+// not from other threads.
+
+// Their transitions and states:
+// _alive    _dead  Set by
+// false     true   Constructor
+// true      false  Run() method entry
+// false     any    Run() method runFunction failure
+// any       false  Run() method exit (happens only with _alive false)
+// false     any    SetNotAlive
+// false     any    Stop         Stop waits for _dead to become true.
+//
+// Summarized a different way:
+// Variable   Writer               Reader
+// _alive     Constructor(false)   Run.loop
+//            Run.start(true)
+//            Run.fail(false)
+//            SetNotAlive(false)
+//            Stop(false)
+//
+// _dead      Constructor(true)    Stop.loop
+//            Run.start(false)
+//            Run.exit(true)
+
 #include "thread_posix.h"
 
 #include <errno.h>

src/system_wrappers/source/thread_unittest.cc

@@ -0,0 +1,93 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "system_wrappers/interface/thread_wrapper.h"
+
+#include "gtest/gtest.h"
+#include "system_wrappers/interface/trace.h"
+
+namespace webrtc {
+
+const int kLogTrace = 1;
+
+class TestTraceCallback : public TraceCallback {
+ public:
+  virtual void Print(const TraceLevel level,
+                     const char* traceString,
+                     const int length) {
+    if (traceString) {
+      char* cmd_print = new char[length+1];
+      memcpy(cmd_print, traceString, length);
+      cmd_print[length] = '\0';
+      printf("%s\n", cmd_print);
+      fflush(stdout);
+      delete[] cmd_print;
+    }
+  }
+};
+
+class ThreadTest : public ::testing::Test {
+ public:
+  ThreadTest() {
+    StartTrace();
+  }
+  ~ThreadTest() {
+    StopTrace();
+  }
+
+ private:
+  void StartTrace() {
+    if (kLogTrace) {
+      Trace::CreateTrace();
+      Trace::SetLevelFilter(webrtc::kTraceAll);
+      Trace::SetTraceCallback(&trace_);
+    }
+  }
+
+  void StopTrace() {
+    if (kLogTrace) {
+      Trace::ReturnTrace();
+    }
+  }
+
+  TestTraceCallback trace_;
+};
+
+// Function that does nothing, and reports success.
+bool NullRunFunction(void* /* obj */) {
+  return true;
+}
+
+TEST_F(ThreadTest, StartStop) {
+  ThreadWrapper* thread = ThreadWrapper::CreateThread(&NullRunFunction);
+  unsigned int id = 42;
+  ASSERT_TRUE(thread->Start(id));
+  EXPECT_TRUE(thread->Stop());
+}
+
+// Function that sets a boolean.
+bool SetFlagRunFunction(void* obj) {
+  bool* obj_as_bool = static_cast<bool*> (obj);
+  *obj_as_bool = true;
+  return true;
+}
+
+TEST_F(ThreadTest, RunFunctionIsCalled) {
+  bool flag = false;
+  ThreadWrapper* thread = ThreadWrapper::CreateThread(&SetFlagRunFunction,
+                                                      &flag);
+  unsigned int id = 42;
+  ASSERT_TRUE(thread->Start(id));
+  // At this point, the flag may be either true or false.
+  EXPECT_TRUE(thread->Stop());
+  // We expect the thread to have run at least once.
+  EXPECT_TRUE(flag);
+}
+
+}  // namespace webrtc