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sMutexLock implementation [message #15998]

Thu, 22 May 2008 10:38

hojtsy
Messages: 241
Registered: January 2006
Location: Budapest, Hungary

Experienced Member

In Mt.cpp there is

Mutex& sMutexLock()
{
	static Mutex *section;
	if(!section) {
		static byte b[sizeof(Mutex)];
		section = new(b) Mutex;
	}
	return *section;
}

How is this different from the simpler

Mutex& sMutexLock()
{
	static Mutex m;
	return m;
}

In both cases the Mutex constructor will be called when the function is first called. In both cases the function needs external protection from MT race conditions.

On a side note, this function is not on the interface (Mt.h), why not make it file static in Mt.cpp to avoid name clashes?

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Re: sMutexLock implementation [message #16178 is a reply to message #15998]

Fri, 30 May 2008 19:11

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

hojtsy wrote on Thu, 22 May 2008 04:38

In Mt.cpp there is

Mutex& sMutexLock()
{
	static Mutex *section;
	if(!section) {
		static byte b[sizeof(Mutex)];
		section = new(b) Mutex;
	}
	return *section;
}

How is this different from the simpler

Mutex& sMutexLock()
{
	static Mutex m;
	return m;
}

I think you are basically right. This was attempt to make more sure that initialization really happens and there is not catch, because external protection is not possible there.... as this is a mutex used to protect synchronization of other mutexes..

So the whole thing is meant to be run before second thread starts (and it is called in several places to ensure this).

I guess it is still better this way, as you never know what really happens in "static magic".

I agree about "static" though.

Mirek

Mirek

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