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multithreading-and-locales.md

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Learn more about: Multithreading and Locales
Multithreading and Locales
11/04/2016
locales [C++], multithreading
multithreading [C++], locales
threading [C++], locales
per-thread locale
d6fb159a-eaca-4130-a51a-f95d62f71485

Multithreading and Locales

Both the C Runtime Library and the C++ Standard Library provide support for changing the locale of your program. This topic discusses issues that arise when using the locale functionality of both libraries in a multithreaded application.

Remarks

With the C Runtime Library, you can create multithreaded applications using the _beginthread and _beginthreadex functions. This topic only covers multithreaded applications created using these functions. For more information, see _beginthread, _beginthreadex.

To change the locale using the C Runtime Library, use the setlocale function. In previous versions of Visual C++, this function would always modify the locale throughout the entire application. There is now support for setting the locale on a per-thread basis. This is done using the _configthreadlocale function. To specify that setlocale should only change the locale in the current thread, call _configthreadlocale(_ENABLE_PER_THREAD_LOCALE) in that thread. Conversely, calling _configthreadlocale(_DISABLE_PER_THREAD_LOCALE) will cause that thread to use the global locale, and any call to setlocale in that thread will change the locale in all threads that have not explicitly enabled per-thread locale.

To change the locale using the C++ Runtime Library, use the locale Class. By calling the locale::global method, you change the locale in every thread that has not explicitly enabled per-thread locale. To change the locale in a single thread or portion of an application, simply create an instance of a locale object in that thread or portion of code.

Note

Calling locale::global changes the locale for both the C++ Standard Library and the C Runtime Library. However, calling setlocale only changes the locale for the C Runtime Library; the C++ Standard Library is not affected.

The following examples show how to use the setlocale function, the locale Class, and the _configthreadlocale function to change the locale of an application in several different scenarios.

Example: Change locale with per-thread locale enabled

In this example, the main thread spawns two child threads. The first thread, Thread A, enables per-thread locale by calling _configthreadlocale(_ENABLE_PER_THREAD_LOCALE). The second thread, Thread B, as well as the main thread, do not enable per-thread locale. Thread A then proceeds to change the locale using the setlocale function of the C Runtime Library.

Since Thread A has per-thread locale enabled, only the C Runtime Library functions in Thread A start using the "french" locale. The C Runtime Library functions in Thread B and in the main thread continue to use the "C" locale. Also, since setlocale does not affect the C++ Standard Library locale, all C++ Standard Library objects continue to use the "C" locale.

// multithread_locale_1.cpp// compile with: /EHsc /MD #include<clocale> #include<cstdio> #include<locale> #include<process.h> #include<windows.h> #defineNUM_THREADS2usingnamespacestd;unsigned __stdcall RunThreadA(void *params); unsigned __stdcall RunThreadB(void *params); BOOL localeSet = FALSE; HANDLE printMutex = CreateMutex(NULL, FALSE, NULL); intmain() { HANDLE threads[NUM_THREADS]; unsigned aID; threads[0] = (HANDLE)_beginthreadex( NULL, 0, RunThreadA, NULL, 0, &aID); unsigned bID; threads[1] = (HANDLE)_beginthreadex( NULL, 0, RunThreadB, NULL, 0, &bID); WaitForMultipleObjects(2, threads, TRUE, INFINITE); printf_s("[Thread main] Per-thread locale is NOT enabled.\n"); printf_s("[Thread main] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread main] locale::global is set to \"%s\"\n", locale().name().c_str()); CloseHandle(threads[0]); CloseHandle(threads[1]); CloseHandle(printMutex); return0; } unsigned __stdcall RunThreadA(void *params) { _configthreadlocale(_ENABLE_PER_THREAD_LOCALE); setlocale(LC_ALL, "french"); localeSet = TRUE; WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread A] Per-thread locale is enabled.\n"); printf_s("[Thread A] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread A] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; } unsigned __stdcall RunThreadB(void *params) { while (!localeSet) Sleep(100); WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread B] Per-thread locale is NOT enabled.\n"); printf_s("[Thread B] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread B] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; }
[Thread A] Per-thread locale is enabled. [Thread A] CRT locale is set to "French_France.1252" [Thread A] locale::global is set to "C" [Thread B] Per-thread locale is NOT enabled. [Thread B] CRT locale is set to "C" [Thread B] locale::global is set to "C" [Thread main] Per-thread locale is NOT enabled. [Thread main] CRT locale is set to "C" [Thread main] locale::global is set to "C"

Example: Change global locale with per-thread locale enabled

In this example, the main thread spawns two child threads. The first thread, Thread A, enables per-thread locale by calling _configthreadlocale(_ENABLE_PER_THREAD_LOCALE). The second thread, Thread B, as well as the main thread, do not enable per-thread locale. Thread A then proceeds to change the locale using the locale::global method of the C++ Standard Library.

Since Thread A has per-thread locale enabled, only the C Runtime Library functions in Thread A start using the "french" locale. The C Runtime Library functions in Thread B and in the main thread continue to use the "C" locale. However, since the locale::global method changes the locale "globally", all C++ Standard Library objects in all threads start using the "french" locale.

// multithread_locale_2.cpp// compile with: /EHsc /MD #include<clocale> #include<cstdio> #include<locale> #include<process.h> #include<windows.h> #defineNUM_THREADS2usingnamespacestd;unsigned __stdcall RunThreadA(void *params); unsigned __stdcall RunThreadB(void *params); BOOL localeSet = FALSE; HANDLE printMutex = CreateMutex(NULL, FALSE, NULL); intmain() { HANDLE threads[NUM_THREADS]; unsigned aID; threads[0] = (HANDLE)_beginthreadex( NULL, 0, RunThreadA, NULL, 0, &aID); unsigned bID; threads[1] = (HANDLE)_beginthreadex( NULL, 0, RunThreadB, NULL, 0, &bID); WaitForMultipleObjects(2, threads, TRUE, INFINITE); printf_s("[Thread main] Per-thread locale is NOT enabled.\n"); printf_s("[Thread main] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread main] locale::global is set to \"%s\"\n", locale().name().c_str()); CloseHandle(threads[0]); CloseHandle(threads[1]); CloseHandle(printMutex); return0; } unsigned __stdcall RunThreadA(void *params) { _configthreadlocale(_ENABLE_PER_THREAD_LOCALE); locale::global(locale("french")); localeSet = TRUE; WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread A] Per-thread locale is enabled.\n"); printf_s("[Thread A] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread A] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; } unsigned __stdcall RunThreadB(void *params) { while (!localeSet) Sleep(100); WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread B] Per-thread locale is NOT enabled.\n"); printf_s("[Thread B] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread B] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; }
[Thread A] Per-thread locale is enabled. [Thread A] CRT locale is set to "French_France.1252" [Thread A] locale::global is set to "French_France.1252" [Thread B] Per-thread locale is NOT enabled. [Thread B] CRT locale is set to "C" [Thread B] locale::global is set to "French_France.1252" [Thread main] Per-thread locale is NOT enabled. [Thread main] CRT locale is set to "C" [Thread main] locale::global is set to "French_France.1252"

Example: Change locale without per-thread locale enabled

In this example, the main thread spawns two child threads. The first thread, Thread A, enables per-thread locale by calling _configthreadlocale(_ENABLE_PER_THREAD_LOCALE). The second thread, Thread B, as well as the main thread, do not enable per-thread locale. Thread B then proceeds to change the locale using the setlocale function of the C Runtime Library.

Since Thread B does not have per-thread locale enabled, the C Runtime Library functions in Thread B and in the main thread start using the "french" locale. The C Runtime Library functions in Thread A continue to use the "C" locale because Thread A has per-thread locale enabled. Also, since setlocale does not affect the C++ Standard Library locale, all C++ Standard Library objects continue to use the "C" locale.

// multithread_locale_3.cpp// compile with: /EHsc /MD #include<clocale> #include<cstdio> #include<locale> #include<process.h> #include<windows.h> #defineNUM_THREADS2usingnamespacestd;unsigned __stdcall RunThreadA(void *params); unsigned __stdcall RunThreadB(void *params); BOOL localeSet = FALSE; BOOL configThreadLocaleCalled = FALSE; HANDLE printMutex = CreateMutex(NULL, FALSE, NULL); intmain() { HANDLE threads[NUM_THREADS]; unsigned aID; threads[0] = (HANDLE)_beginthreadex( NULL, 0, RunThreadA, NULL, 0, &aID); unsigned bID; threads[1] = (HANDLE)_beginthreadex( NULL, 0, RunThreadB, NULL, 0, &bID); WaitForMultipleObjects(2, threads, TRUE, INFINITE); printf_s("[Thread main] Per-thread locale is NOT enabled.\n"); printf_s("[Thread main] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread main] locale::global is set to \"%s\"\n", locale().name().c_str()); CloseHandle(threads[0]); CloseHandle(threads[1]); CloseHandle(printMutex); return0; } unsigned __stdcall RunThreadA(void *params) { _configthreadlocale(_ENABLE_PER_THREAD_LOCALE); configThreadLocaleCalled = TRUE; while (!localeSet) Sleep(100); WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread A] Per-thread locale is enabled.\n"); printf_s("[Thread A] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread A] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; } unsigned __stdcall RunThreadB(void *params) { while (!configThreadLocaleCalled) Sleep(100); setlocale(LC_ALL, "french"); localeSet = TRUE; WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread B] Per-thread locale is NOT enabled.\n"); printf_s("[Thread B] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread B] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; }
[Thread B] Per-thread locale is NOT enabled. [Thread B] CRT locale is set to "French_France.1252" [Thread B] locale::global is set to "C" [Thread A] Per-thread locale is enabled. [Thread A] CRT locale is set to "C" [Thread A] locale::global is set to "C" [Thread main] Per-thread locale is NOT enabled. [Thread main] CRT locale is set to "French_France.1252" [Thread main] locale::global is set to "C"

Example: Change global locale without per-thread locale enabled

In this example, the main thread spawns two child threads. The first thread, Thread A, enables per-thread locale by calling _configthreadlocale(_ENABLE_PER_THREAD_LOCALE). The second thread, Thread B, as well as the main thread, do not enable per-thread locale. Thread B then proceeds to change the locale using the locale::global method of the C++ Standard Library.

Since Thread B does not have per-thread locale enabled, the C Runtime Library functions in Thread B and in the main thread start using the "french" locale. The C Runtime Library functions in Thread A continue to use the "C" locale because Thread A has per-thread locale enabled. However, since the locale::global method changes the locale "globally", all C++ Standard Library objects in all threads start using the "french" locale.

// multithread_locale_4.cpp// compile with: /EHsc /MD #include<clocale> #include<cstdio> #include<locale> #include<process.h> #include<windows.h> #defineNUM_THREADS2usingnamespacestd;unsigned __stdcall RunThreadA(void *params); unsigned __stdcall RunThreadB(void *params); BOOL localeSet = FALSE; BOOL configThreadLocaleCalled = FALSE; HANDLE printMutex = CreateMutex(NULL, FALSE, NULL); intmain() { HANDLE threads[NUM_THREADS]; unsigned aID; threads[0] = (HANDLE)_beginthreadex( NULL, 0, RunThreadA, NULL, 0, &aID); unsigned bID; threads[1] = (HANDLE)_beginthreadex( NULL, 0, RunThreadB, NULL, 0, &bID); WaitForMultipleObjects(2, threads, TRUE, INFINITE); printf_s("[Thread main] Per-thread locale is NOT enabled.\n"); printf_s("[Thread main] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread main] locale::global is set to \"%s\"\n", locale().name().c_str()); CloseHandle(threads[0]); CloseHandle(threads[1]); CloseHandle(printMutex); return0; } unsigned __stdcall RunThreadA(void *params) { _configthreadlocale(_ENABLE_PER_THREAD_LOCALE); configThreadLocaleCalled = TRUE; while (!localeSet) Sleep(100); WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread A] Per-thread locale is enabled.\n"); printf_s("[Thread A] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread A] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; } unsigned __stdcall RunThreadB(void *params) { while (!configThreadLocaleCalled) Sleep(100); locale::global(locale("french")); localeSet = TRUE; WaitForSingleObject(printMutex, INFINITE); printf_s("[Thread B] Per-thread locale is NOT enabled.\n"); printf_s("[Thread B] CRT locale is set to \"%s\"\n", setlocale(LC_ALL, NULL)); printf_s("[Thread B] locale::global is set to \"%s\"\n\n", locale().name().c_str()); ReleaseMutex(printMutex); return1; }
[Thread B] Per-thread locale is NOT enabled. [Thread B] CRT locale is set to "French_France.1252" [Thread B] locale::global is set to "French_France.1252" [Thread A] Per-thread locale is enabled. [Thread A] CRT locale is set to "C" [Thread A] locale::global is set to "French_France.1252" [Thread main] Per-thread locale is NOT enabled. [Thread main] CRT locale is set to "French_France.1252" [Thread main] locale::global is set to "French_France.1252"

See also

Multithreading Support for Older Code (Visual C++)
_beginthread, _beginthreadex
_configthreadlocale
setlocale
Internationalization
Locale
<clocale>
<locale>
locale Class

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