Merge pull request #984 from openzim/namedthread_bugfix

Fixed the race condition in NamedThread

Author: veloman-yunkan

src/namedthread.cpp

@@ -38,6 +38,12 @@ std::map<std::thread::id, std::string> threadId2NameMap_;
 
 } // unnamed namespace
 
+
+std::mutex& NamedThread::getMutex()
+{
+  return mutex_;
+}
+
 NamedThread::NamedThread(const std::string& name)
   : name_(name)
 {

src/namedthread.h

@@ -20,6 +20,7 @@
 #ifndef OPENZIM_LIBZIM_NAMEDTHREAD_H
 #define OPENZIM_LIBZIM_NAMEDTHREAD_H
 
+#include <mutex>
 #include <string>
 #include <thread>
 
@@ -34,11 +35,18 @@ class LIBZIM_PRIVATE_API NamedThread
   explicit NamedThread(const std::string& name);
 
 public:
-  template <class F, class... Args>
-  NamedThread(const std::string& name, F&& f, Args&&... args)
+  template <class F>
+  NamedThread(const std::string& name, F&& f)
     : NamedThread(name)
   {
-    thread_ = std::thread(std::forward<F>(f), std::forward<Args>(args)...);
+    // Ensure that f starts executing after the assignment to
+    // the thread_ data member has completed (so that any possible
+    // calls to NamedThread::getCurrentThreadName() from inside f()
+    // read the correct value of thread id).
+    std::mutex& mutex = getMutex();
+    std::lock_guard<std::mutex> lock(mutex);
+
+    thread_ = std::thread([f, &mutex]() { mutex.lock(); mutex.unlock(); f(); });
   }
 
   ~NamedThread();
@@ -50,7 +58,13 @@ class LIBZIM_PRIVATE_API NamedThread
 
   static std::string getCurrentThreadName();
 
-private:
+private: // functions
+  // This is a workaround for a bug in our build system that prevents
+  // LIBZIM_PRIVATE_API and/or LIBZIM_API classes from having static data
+  // members
+  static std::mutex& getMutex();
+
+private: // data
   const std::string name_;
   std::thread thread_;
 };