BUG: _wsetlocale Is Not Threadsafe

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View products that this article applies to.

This article was previously published under Q304497

SYMPTOMS

A heap corruption can occur if _wsetlocale is called simultaneously from multiple threads.

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CAUSE

_wsetlocale does not synchronize access to a local static variable, outwlocale.

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RESOLUTION

To work around this, you must synchronize calls to _wsetlocale.

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

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The C Runtime locale mechanism in Microsoft Visual C++ is distinct from the locale mechanism in Microsoft Windows. Though Windows supports per-thread locales, C Runtime supports only a single global locale for any program.

If multiple threads call _wsetlocale, then no thread's locale can be trusted. For example, if one thread calls _wsetlocale for French and tries to use that locale for _wcslwr, and another thread calls _wsetlocale for English before the first thread executes the _wcslwr function call, then the first thread uses the English locale instead of the French locale.

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Steps to Reproduce the Behavior


#define _UNICODE
#include <stdio.h>
#include <locale.h>
#include <process.h>

void __cdecl test(void *i) {
	_wsetlocale(LC_ALL, L"English");
	_wsetlocale(LC_ALL, L"French");
	_wsetlocale(LC_ALL, L"German");
	_wsetlocale(LC_ALL, L"English");
	printf("%d exit\n",i);
}

void wmain () {
	for (int i=0; i<30; ++i) _beginthread(test,0,(void*)i);
	getchar();
}

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APPLIES TO

Microsoft Visual C++ 6.0 Service Pack 5

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kbbug kbfix KB304497

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Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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