fix possible deadlock for OD.

Also comment related cleanups.

src/ondemand/ODManager.cpp

@@ -259,12 +259,12 @@ void ODManager::Start()
       mTasksMutex.Lock();
       tasksInArray = mTasks.size()>0;
       mTasksMutex.Unlock();
-      mCurrentThreadsMutex.Lock();
 
       mPauseLock.Lock();
       paused=mPause;
       mPauseLock.Unlock();
 
+      mCurrentThreadsMutex.Lock();
       // keep adding tasks if there is work to do, up to the limit.
       while(!paused && tasksInArray && (mCurrentThreads < mMaxThreads))
       {

src/ondemand/ODManager.h

@@ -45,6 +45,7 @@ class ODManager
  public:
    ///Gets the singleton instance - this is a function pointer that points to one of the below two instance calls.
    ///Note that it is not a member function pointer since it is a static function.
+   ///the function pointer swapping is valid as long as the initial calls only happen from the main thread.
    static ODManager* (*Instance)();
    ///Gets the singleton instance
    static ODManager* InstanceFirstTime();
@@ -192,6 +193,7 @@ class ODManagerHelperThread {
    static void *callback(void *p) {
       ODManagerHelperThread *th = (ODManagerHelperThread *)p;
       /* return (void *) */th->Entry();
+      return NULL;
    }
 
    ///Specifies the priority the thread will run at.  Currently doesn't work.