How to implement a unmanaged thread-safe collection when I get this error: <mutex> is not supported when compiling with /clr

Question

I have a C++ application which consists of unmanaged C++, managed C++ and c#. In the unmanaged part I'm trying to create a thread safe collection using std::mutex.

However when I use the mutex I get the following error;

error C1189: #error : <mutex> is not supported when compiling with /clr or /clr:pure.

Any idea why I can't use the mutex? Can someone recommend a replacement for it so that I can create a thread-safe unmanaged collection?

Answer 1

It is not supported because the std::mutex implementation uses GetCurrentThreadId(). That's a winapi function that is not supposed to be use in managed code since it might be running on a custom CLR host that doesn't use threads to implement threading.

This is the good kind of problem to have, it shows that you are building your code wrong. Your native C++ is being compiled with /clr in effect. Which works rather too well, all C++03 compliant code can be compiled to MSIL and get just-in-time compiled at runtime, just like managed code. You don't want this to happen, your native C++ code should be compiled to machine code and get the compile-time code optimizer love.

Turn off the /clr option for this source code file, and possibly others, in your project. Right-click + Properties, General. If the mutex appears in the .h file that you have to #include in a C++/CLI source file then you have a bigger problem, use an interface or pimpl to hide implementation details.