类似信号量互斥的问题，有没有现成的只读锁可以用？
现在需要设置多线程互斥访问一部分数据，但是大部分线程都是读操作，所以这些线程可以同时访问这些数据，另外又存在一些写操作的线程，不仅这些线程之间需要互斥，而且也需要与读操作的线程进行互斥。
有没有现成的类或者API可以直接拿来用的呢？
[解决办法]
更正：
应该是CSWMRG类：
/******************************************************************************Module: SWMRG.hNotices: Copyright (c) 2000 Jeffrey Richter******************************************************************************/#pragma once///////////////////////////////////////////////////////////////////////////////class CSWMRG {public: CSWMRG(); // Constructor ~CSWMRG(); // Destructor VOID WaitToRead(); // Call this to gain shared read access VOID WaitToWrite(); // Call this to gain exclusive write access VOID Done(); // Call this when done accessing the resourceprivate: CRITICAL_SECTION m_cs; // Permits exclusive access to other members HANDLE m_hsemReaders; // Readers wait on this if a writer has access HANDLE m_hsemWriters; // Writers wait on this if a reader has access int m_nWaitingReaders; // Number of readers waiting for access int m_nWaitingWriters; // Number of writers waiting for access int m_nActive; // Number of threads currently with access // (0=no threads, >0=# of readers, -1=1 writer)};//////////////////////////////// End of File ///////////////////////////////////******************************************************************************Module: SWMRG.cppNotices: Copyright (c) 2000 Jeffrey Richter******************************************************************************/#include "..\CmnHdr.h" /* See Appendix A. */#include "SWMRG.h"///////////////////////////////////////////////////////////////////////////////CSWMRG::CSWMRG() { // Initially no readers want access, no writers want access, and // no threads are accessing the resource m_nWaitingReaders = m_nWaitingWriters = m_nActive = 0; m_hsemReaders = CreateSemaphore(NULL, 0, MAXLONG, NULL); m_hsemWriters = CreateSemaphore(NULL, 0, MAXLONG, NULL); InitializeCriticalSection(&m_cs);}///////////////////////////////////////////////////////////////////////////////CSWMRG::~CSWMRG() {#ifdef _DEBUG // A SWMRG shouldn't be destroyed if any threads are using the resource if (m_nActive != 0) DebugBreak();#endif m_nWaitingReaders = m_nWaitingWriters = m_nActive = 0; DeleteCriticalSection(&m_cs); CloseHandle(m_hsemReaders); CloseHandle(m_hsemWriters);}///////////////////////////////////////////////////////////////////////////////VOID CSWMRG::WaitToRead() { // Ensure exclusive access to the member variables EnterCriticalSection(&m_cs); // Are there writers waiting or is a writer writing? BOOL fResourceWritePending = (m_nWaitingWriters || (m_nActive < 0)); if (fResourceWritePending) { // This reader must wait, increment the count of waiting readers m_nWaitingReaders++; } else { // This reader can read, increment the count of active readers m_nActive++; } // Allow other threads to attempt reading/writing LeaveCriticalSection(&m_cs); if (fResourceWritePending) { // This thread must wait WaitForSingleObject(m_hsemReaders, INFINITE); }}///////////////////////////////////////////////////////////////////////////////VOID CSWMRG::WaitToWrite() { // Ensure exclusive access to the member variables EnterCriticalSection(&m_cs); // Are there any threads accessing the resource? BOOL fResourceOwned = (m_nActive != 0); if (fResourceOwned) { // This writer must wait, increment the count of waiting writers m_nWaitingWriters++; } else { // This writer can write, decrement the count of active writers m_nActive = -1; } // Allow other threads to attempt reading/writing LeaveCriticalSection(&m_cs); if (fResourceOwned) { // This thread must wait WaitForSingleObject(m_hsemWriters, INFINITE); }}///////////////////////////////////////////////////////////////////////////////VOID CSWMRG::Done() { // Ensure exclusive access to the member variables EnterCriticalSection(&m_cs); if (m_nActive > 0) { // Readers have control so a reader must be done m_nActive--; } else { // Writers have control so a writer must be done m_nActive++; } HANDLE hsem = NULL; // Assume no threads are waiting LONG lCount = 1; // Assume only 1 waiter wakes; always true for writers if (m_nActive == 0) { // No thread has access, who should wake up? // NOTE: It is possible that readers could never get access // if there are always writers wanting to write if (m_nWaitingWriters > 0) { // Writers are waiting and they take priority over readers m_nActive = -1; // A writer will get access m_nWaitingWriters--; // One less writer will be waiting hsem = m_hsemWriters; // Writers wait on this semaphore // NOTE: The semaphore will release only 1 writer thread } else if (m_nWaitingReaders > 0) { // Readers are waiting and no writers are waiting m_nActive = m_nWaitingReaders; // All readers will get access m_nWaitingReaders = 0; // No readers will be waiting hsem = m_hsemReaders; // Readers wait on this semaphore lCount = m_nActive; // Semaphore releases all readers } else { // There are no threads waiting at all; no semaphore gets released } } // Allow other threads to attempt reading/writing LeaveCriticalSection(&m_cs); if (hsem != NULL) { // Some threads are to be released ReleaseSemaphore(hsem, lCount, NULL); }}//////////////////////////////// End of File //////////////////////////////////