std::mutex::lock fails on Windows, error code 3

Question

I use std::mutex and std::lock_guard in a proper RAII manner throughout my application:

struct Foo {
    int f() const
    {
       std::lock_guard<std::mutex> locker(m_mutex);
       return m_i;
    }
private:
   int m_i = 0;
   mutable std::mutex m_mutex;
};

It always worked, but I've added parallelism to one more class just now, and in this new class locker throws std::system_error. The problem is here (xthread header):

inline int _Mtx_lockX(_Mtx_t *_Mtx)
{   // throw exception on failure
    return (_Check_C_return(_Mtx_lock(_Mtx)));
}

_Mtx_lock returns 3 while the expected value is 0. No idea what 3 means.

VS2013, v120_x64 runtime.

Give us enough code to reproduce the problem. Or check the call stack when the error occurs and it may be obvious. — David Schwartz, Jun 09 '15 at 19:41
Make your mutex mutable... You're modifying it's state from a const function. It should not compile, imo — Werner Erasmus, Jun 09 '15 at 19:41
Also, might be compiler issue. I'll write default constructor that default initialize mutex. — Werner Erasmus, Jun 09 '15 at 19:44
@WernerErasmus: well sure it is mutable, I thought that's obvious enough to omit from the question. — Violet Giraffe, Jun 09 '15 at 20:15
@DavidSchwartz: I can't give you enough code to reproduce the problem, it's a decently big project and I don't have a slightest idea what triggers the issue. Which is why I need to know what error code 3 means. The callstack is perfectly fine, except return code is 0 for success and 3 when it fails. — Violet Giraffe, Jun 09 '15 at 20:16
@VioletGiraffe, accepted, but giving us code that doesn't compile detracts us from the real problem. — Werner Erasmus, Jun 09 '15 at 20:18
@WernerErasmus: right, I'll do my best avoiding low quality code snippets in my questions. As for the underscore prefix, it doesn't seem to be forbidden in local scope: http://stackoverflow.com/a/228797/634821 — Violet Giraffe, Jun 09 '15 at 20:22
If anyone wants to experiment, it's an open-source project on Github. I could simply commit the faulty code. It needs Qt to compile, though. — Violet Giraffe, Jun 09 '15 at 20:25
Error code 3 seems to be the value of `_Thrd_busy` at the top of xthreads.h. — phantom, Jun 09 '15 at 20:30
@VioletGiraffe. In the code presented I see no obvious errors. I might clone the project some time. I have Qt. Could it be that mutex is locked recursively? Does not seem that way in code presented. I can't find documentation for the return values of Mtx_lockx — Werner Erasmus, Jun 09 '15 at 20:33
@VioletGiraffe Did you look closely at every function in the callstack to see if it's doing anything related to the mutex? — David Schwartz, Jun 09 '15 at 20:55

score 21 · Accepted Answer · edited May 23 '17 at 12:09

21

The error as mentioned by @Phantom (_Thrd_busy) implies that the lock had been recursively taken. Also see this answer

edited May 23 '17 at 12:09

Community

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answered Jun 09 '15 at 20:36

Werner Erasmus

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That's it, switching to `std::recursive_mutex` solved the problem! I should probably refactor my code to avoid recursive locking. – Violet Giraffe Jun 09 '15 at 20:55

std::mutex::lock fails on Windows, error code 3

1 Answers1