c++ std::thread with static member hangs - c++

Question

I'm trying to creating a logging class where the call to write a log is static. Now, due to performance requirements I'm want to perform the actual logging in a separate thread. Since the function to write to a log is static, I think the thread also needs to be static, which is also tied to another static member function that performs the actual writing of the log. I tried coding it but somehow it hangs during the initialization of the static thread. The code sample that duplicates the behavior is below:
"Logger.h"
#ifndef LOGGER_H
#define LOGGER_H
#include <condition_variable>
#include <mutex>
#include <queue>
#include <string>
#include <thread>
#include <vector>
#define LIBRARY_EXPORTS
#ifdef LIBRARY_EXPORTS // inside DLL
#define LIBRARY_API __declspec(dllexport)
#else // outside DLL
#define LIBRARY_API __declspec(dllimport)
#endif
using namespace std;
namespace Company { namespace Logging {
class LIBRARY_API Logger
{
public:
~Logger();
void static Write(string message, vector<string> categories = vector<string>());
private:
Logger();
Logger(Logger const&) {}
void operator=(Logger const&) {}
static thread processLogEntriesThread;
static void ProcessLogEntries();
};
}}
#endif
"Logger.cpp"
#include "Logger.h"
#include <iostream>
using namespace std;
namespace Company { namespace Logging {
thread Logger::processLogEntriesThread = thread(&Logger::ProcessLogEntries);
Logger::Logger()
{
}
Logger::~Logger()
{
Logger::processLogEntriesThread.join();
}
void Logger::Write(string message, vector<string> categories)
{
cout << message << endl;
}
void Logger::ProcessLogEntries()
{
}
}}
One odd behavior that I found is that the hanging part only happens when the class packaged in a DLL. If I use the class files directly into the console EXE project it seems to be working.
So basically my problem is the hanging part and if I'm doing things correctly.
Thanks in advance...

Answer 1

you can use my logger library => https://github.com/PraGitHub/Prapository/tree/master/C_Cpp/Logger
If this post is found irrelevant, please pardon me.

Answer 2

the hanging part only happens when the class packaged in a DLL
See Dynamic-Link Library Best Practices for full details why it hangs:
You should never perform the following tasks from within DllMain:
Call CreateThread. Creating a thread can work if you do not synchronize with other threads, but it is risky.
The solution is provide an initialization function/object for your logger library that the user must call explicitly in main, rather than having a global thread object initialized before main is entered. This function should create the thread.
Or create the thread on the first logging call using std::call_once. However, this involves an extra conditional check on each logging call. This check may be cheap but it is not free.

Answer 3

I can not see any usage of the logger thread. Having a thread as member in a class did not mean that all member functions will run in the created thread. The destructor of logger will never called, while you have no logger instance. iostream is not thread safe!
What you have to do:
Create some kind of storage to collect the logging infos. This instance must be thread safe!
Push messages from the outside world into this instance. The instance itself must have a own thread which reads from the storage and put the data to the output. This must be done also in a thread safe manner because reading and writing comes from different threads!