SRW Lock 可以用作二進制信號量嗎？

Question

Slim Reader/Writer (SRW) Locks是 Windows 中的同步原語，從 Windows Vista 開始可用。

名稱和接口表明它應該用作非定時共享非遞歸互斥鎖。 但是，通常也將其用作非共享互斥體，以避免CRTICAL_SECTION開銷（僅使用獨占 API）。

我注意到它也可以用作二進制信號量。 This can come handy, as other semaphores available in Windows APIs - Event object and Semaphore object - are always a kernel call, so it is probably the only lightweight semaphore readily available from Windows API (and C++ has semaphores starting C++20, and boost 線程也不提供信號量）。

但這可靠嗎？ 具體來說，我沒有在文檔中找到可以以這種方式使用它的明確信息。

但是，我沒有發現任何禁止這種用法的東西。 文檔似乎不確定。

我期望的答案是：

• 也許有人可以指出允許或禁止使用信號量的文檔措辭
• 也許有這種用法的一些實際經驗
• 也許直接參與 SRW 鎖實現的人可以澄清（我認為有一些機會）

---

示例 - 這不會掛起

#include <Windows.h>
#include <atomic>


SRWLOCK lock = SRWLOCK_INIT;

std::atomic<bool> can_release{ false };

DWORD CALLBACK Thread1(LPVOID)
{
    for (int i = 0; i < 3; i++)
    {
        while (!can_release)
        {
            // spin
        }
        can_release = false;
        ::ReleaseSRWLockExclusive(&lock);
    }

    return 0;
}


DWORD CALLBACK Thread2(LPVOID)
{
    for (int i = 0; i < 3; i++)
    {
        can_release = true;
        ::AcquireSRWLockExclusive(&lock);
    }

    return 0;
}

int main() {
    ::AcquireSRWLockExclusive(&lock);

    HANDLE h1 = ::CreateThread(nullptr, 0, Thread1, nullptr, 0, nullptr);
    HANDLE h2 = ::CreateThread(nullptr, 0, Thread2, nullptr, 0, nullptr);

    ::WaitForSingleObject(h1, INFINITE);
    ::WaitForSingleObject(h2, INFINITE);

    ::CloseHandle(h1);
    ::CloseHandle(h2);
    
    return 0;
}

Answer 1

@Raymond Chen 是對的。 應用程序驗證程序報告相關代碼的錯誤：

有問題的代碼會產生此錯誤：

=======================================
VERIFIER STOP 0000000000000255: pid 0x1A44: The SRW lock being released was not acquired by this thread. 

    00007FF73979C170 : SRW Lock
    00000000000025CC : Current ThreadId.
    00000000000043F4 : ThreadId of the thread that acquired the SRW lock.
    000001C1BEA8BF40 : Address of the acquire stack trace. Use dps <address> to see where the SRW lock was acquired.


=======================================
This verifier stop is continuable.
After debugging it use `go' to continue.

=======================================



=======================================
VERIFIER STOP 0000000000000253: pid 0x1A44: The SRW lock is being acquired recursively by the same thread. 

    00007FF73979C170 : SRW Lock
    000001C1BEA8BF40 : Address of the first acquire stack trace. Use dps <address> to see where the SRW lock was acquired.
    0000000000000000 : Not used
    0000000000000000 : Not used


=======================================
This verifier stop is continuable.
After debugging it use `go' to continue.

=======================================

---

截至目前，該文檔還明確禁止在不同的線程中發布，請參閱ReleaseSRWLockExclusive 、 ReleaseSRWLockShared ：

SRW 鎖必須由獲得它的同一線程釋放。 您可以使用 Application Verifier 來幫助驗證您的程序是否正確使用 SRW 鎖（從 Basic 組啟用 Locks checker）。