Re: A few questions about singletons...

"Chris M. Thomasson" <no@spam.invalid>
Fri, 2 Oct 2009 00:56:26 -0700
"Michael Doubez" <> wrote in message
On 30 sep, 01:48, "Chris M. Thomasson" <n...@spam.invalid> wrote:

if (! m_mutex)


I wondered about this usage of assert() + unexpected(): what is the
rational of using both ?

I made several *mistakes in the "hard" error handling code. Sorry about

To tell the truth, I never use std::unexpected(). How and when do you
use it ?

Quite frankly, I personally do not know which exception to throw as I am not
a C++ expert. I decorated the constructor/destructor and `prv_get_name()'
functions with the `throw()' clause. IMVHO, if the ctor of a singleton
fails, then end user program is in peril. Should the singleton ctor throw or

BTW, here is corrected code:
#include <windows.h>
#include <sstream>
#include <iostream>
#include <cstdio>

# include <cassert>
# include <exception>
# define WIN_DCL_MUTEX_UNEXPECTED assert(false), std::unexpected

class win_dcl_mutex
    HANDLE m_mutex;

    template<typename T>
    static std::string prv_get_name(T const& id) throw()
        std::ostringstream name;

        name << "DCL_MUTEX_" << GetCurrentProcessId() << "_" << id;

        // std::cout << name.str() << std::endl;

        return name.str();

    template<typename T>
    win_dcl_mutex(T const& id) throw()

    : m_mutex(CreateMutex(NULL, TRUE, prv_get_name(id).c_str()))

        if (! m_mutex)

        else if (GetLastError() == ERROR_ALREADY_EXISTS)
            if (WaitForSingleObject(m_mutex, INFINITE) !=

    ~win_dcl_mutex() throw()
        if (! ReleaseMutex(m_mutex))

        if (! CloseHandle(m_mutex))

        win_dcl_mutex mutex(12345);

    return 0;


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