428 lines
11 KiB
C
428 lines
11 KiB
C
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/*++
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Copyright (c) 2000, Microsoft Corporation
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Module Name:
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Abstract:
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The file contains the READ_WRITE_LOCK definition which allows
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multiple-reader/single-writer. This implementation DOES NOT
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starve a thread trying to acquire write accesss if there are
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a large number of threads interested in acquiring read access.
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Revision History:
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mohitt, sachins, Apr 23 2000, Created
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--*/
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#include "pcheapol.h"
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#pragma hdrstop
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//----------------------------------------------------------------------------
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// Function: CreateReadWriteLock
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//
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// Initializes a multiple-reader/single-writer lock object
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//----------------------------------------------------------------------------
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DWORD
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CreateReadWriteLock(
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PREAD_WRITE_LOCK pRWL,
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PCHAR szName
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)
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{
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sprintf(pRWL->RWL_Name, "%.3s", szName);
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pRWL->RWL_ReaderCount = 0;
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__try {
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InitializeCriticalSection(&(pRWL)->RWL_ReadWriteBlock);
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}
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__except(EXCEPTION_EXECUTE_HANDLER) {
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return GetLastError();
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}
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pRWL->RWL_ReaderDoneEvent = CreateEvent(NULL,FALSE,FALSE,NULL);
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if (pRWL->RWL_ReaderDoneEvent != NULL) {
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return GetLastError();
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}
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return NO_ERROR;
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}
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//----------------------------------------------------------------------------
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// Function: DeleteReadWriteLock
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//
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// Frees resources used by a multiple-reader/single-writer lock object
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//----------------------------------------------------------------------------
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VOID
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DeleteReadWriteLock(
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PREAD_WRITE_LOCK pRWL
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)
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{
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CloseHandle(pRWL->RWL_ReaderDoneEvent);
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pRWL->RWL_ReaderDoneEvent = NULL;
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DeleteCriticalSection(&pRWL->RWL_ReadWriteBlock);
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pRWL->RWL_ReaderCount = 0;
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}
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//----------------------------------------------------------------------------
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// Function: AcquireReadLock
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//
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// Secures shared ownership of the lock object for the caller.
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//
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// readers enter the read-write critical section, increment the count,
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// and leave the critical section
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//----------------------------------------------------------------------------
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VOID
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AcquireReadLock(
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PREAD_WRITE_LOCK pRWL
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)
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{
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EnterCriticalSection(&pRWL->RWL_ReadWriteBlock);
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InterlockedIncrement(&pRWL->RWL_ReaderCount);
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LeaveCriticalSection(&pRWL->RWL_ReadWriteBlock);
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}
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//----------------------------------------------------------------------------
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// Function: ReleaseReadLock
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//
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// Relinquishes shared ownership of the lock object.
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//
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// the last reader sets the event to wake any waiting writers
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//----------------------------------------------------------------------------
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VOID
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ReleaseReadLock(
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PREAD_WRITE_LOCK pRWL
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)
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{
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if (InterlockedDecrement(&pRWL->RWL_ReaderCount) < 0) {
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SetEvent(pRWL->RWL_ReaderDoneEvent);
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}
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}
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//----------------------------------------------------------------------------
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// Function: AcquireWriteLock
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//
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// Secures exclusive ownership of the lock object.
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//
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// the writer blocks other threads by entering the ReadWriteBlock section,
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// and then waits for any thread(s) owning the lock to finish
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//----------------------------------------------------------------------------
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VOID
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AcquireWriteLock(
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PREAD_WRITE_LOCK pRWL
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)
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{
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EnterCriticalSection(&pRWL->RWL_ReadWriteBlock);
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if (InterlockedDecrement(&pRWL->RWL_ReaderCount) >= 0) {
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WaitForSingleObject(pRWL->RWL_ReaderDoneEvent, INFINITE);
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}
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}
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//----------------------------------------------------------------------------
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// Function: ReleaseWriteLock
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//
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// Relinquishes exclusive ownership of the lock object.
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//
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// the writer releases the lock by setting the count to zero
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// and then leaving the ReadWriteBlock critical section
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//----------------------------------------------------------------------------
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VOID
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ReleaseWriteLock(
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PREAD_WRITE_LOCK pRWL
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)
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{
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InterlockedIncrement(&pRWL->RWL_ReaderCount);
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LeaveCriticalSection(&(pRWL)->RWL_ReadWriteBlock);
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}
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#if 0
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//----------------------------------------------------------------------------
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// InitializeDynamicLocksStore
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//
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// Initialize the structure from which dynamic readwrite locks are allocated.
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//----------------------------------------------------------------------------
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DWORD
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InitializeDynamicLocksStore (
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PDYNAMIC_LOCKS_STORE pStore,
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HANDLE hHeap,
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PCHAR szName
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)
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{
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sprintf(pStore->szName, "%.3s", szName);
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// initialize the heap from where dynamic locks are allocated
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pStore->hHeap = hHeap;
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INITIALIZE_LOCKED_LIST(&pStore->llFreeLocksList, szName);
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if (!LOCKED_LIST_INITIALIZED(&pStore->llFreeLocksList))
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return GetLastError();
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// initialize the count of the number of free and allocated locks
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pStore->ulCountAllocated = pStore->ulCountFree = 0;
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return NO_ERROR;
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}
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//----------------------------------------------------------------------------
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// DeInitializeDynamicLocksStore
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//
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// Fail if any allocated locks have not been freed.
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// Delete the free locks and the FreeLocksList.
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//----------------------------------------------------------------------------
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DWORD
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DeInitializeDynamicLocksStore (
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PDYNAMIC_LOCKS_STORE pStore
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)
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{
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PDYNAMIC_READWRITE_LOCK pLock;
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PLIST_ENTRY pleHead, ple;
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// can't complete if any locks are still allocated!!!
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if (pStore->ulCountAllocated)
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return ERROR_CAN_NOT_COMPLETE;
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// deinitialize the count of the number of free and allocated locks
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pStore->ulCountAllocated = pStore->ulCountFree = 0;
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// deinitialize the FreeLocksList
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pStore->llFreeLocksList.created = 0;
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// delete all dynamic readwrite locks and free the memory.
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pleHead = &(pStore->llFreeLocksList.head);
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for (ple = pleHead->Flink; ple != pleHead; ple = ple->Flink)
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{
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pLock = CONTAINING_RECORD(ple, DYNAMIC_READWRITE_LOCK, leLink);
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DELETE_READ_WRITE_LOCK(&pLock->rwlLock);
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HeapFree(pStore->hHeap, 0, pLock);
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}
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DeleteCriticalSection(&(pStore->llFreeLocksList.lock));
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// deinitialize the heap from where dynamic locks are allocated
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pStore->hHeap = NULL;
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return NO_ERROR;
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}
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//----------------------------------------------------------------------------
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// GetDynamicReadwriteLock
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//
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// Return a free dynamic readwrite lock, if one is available.
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// Else allocate a new dynamic readwrite lock.
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// Assumes pStore->llFreeLocksList is locked.
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//----------------------------------------------------------------------------
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PDYNAMIC_READWRITE_LOCK
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GetDynamicReadwriteLock (
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PDYNAMIC_LOCKS_STORE pStore
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)
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{
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PDYNAMIC_READWRITE_LOCK pLock;
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PLIST_ENTRY pleHead, ple;
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do // breakout loop
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{
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// a free dynamic lock is available. Return it
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pleHead = &(pStore->llFreeLocksList.head);
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if (!IsListEmpty(pleHead))
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{
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pStore->ulCountFree--;
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ple = RemoveHeadList(pleHead);
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pLock = CONTAINING_RECORD(ple, DYNAMIC_READWRITE_LOCK, leLink);
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break;
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}
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// allocate memory for a new dynamic lock
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pLock = HeapAlloc(pStore->hHeap, 0, sizeof(DYNAMIC_READWRITE_LOCK));
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if (pLock == NULL)
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break;
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// initialize the fields
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CREATE_READ_WRITE_LOCK(&(pLock->rwlLock), pStore->szName);
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if (!READ_WRITE_LOCK_CREATED(&(pLock->rwlLock)))
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{
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HeapFree(pStore->hHeap, 0, pLock);
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pLock = NULL;
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break;
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}
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} while (FALSE);
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if (pLock != NULL)
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{
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pStore->ulCountAllocated++;
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pLock->ulCount = 0;
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}
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return pLock;
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}
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//----------------------------------------------------------------------------
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// FreeDynamicReadwriteLock
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//
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// Accepts a released dynamic readwrite lock.
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// Frees it if there are too many dynamic readwrite locks.
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// Assumes pStore->llFreeLocksList is locked.
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//----------------------------------------------------------------------------
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VOID
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FreeDynamicReadwriteLock (
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PDYNAMIC_READWRITE_LOCK pLock,
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PDYNAMIC_LOCKS_STORE pStore
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)
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{
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PLIST_ENTRY pleHead;
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// decrement count of allocated locks
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pStore->ulCountAllocated--;
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// if there are too many dynamic readwrite locks, then free this lock
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if ((pStore->ulCountAllocated + pStore->ulCountFree + 1) >
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DYNAMIC_LOCKS_HIGH_THRESHOLD)
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{
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DELETE_READ_WRITE_LOCK(&pLock->rwlLock);
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HeapFree(pStore->hHeap, 0, pLock);
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}
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else // insert into the list of free locks
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{
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pleHead = &(pStore->llFreeLocksList.head);
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InsertHeadList(pleHead, &pLock->leLink);
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pStore->ulCountFree++;
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}
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return;
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}
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//----------------------------------------------------------------------------
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// AcquireDynamicLock
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//
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// Locks the FreeLocksList.
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// Allocates a new dynamic lock if required.
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// Increments the count.
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// Unlocks the FreeLocksList.
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// Acquires the dynamic lock.
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//----------------------------------------------------------------------------
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DWORD
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AcquireDynamicReadwriteLock (
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PDYNAMIC_READWRITE_LOCK *ppLock,
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LOCK_MODE lmMode,
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PDYNAMIC_LOCKS_STORE pStore
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)
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{
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// acquire the lock for the free locks list
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AcquireListLock(&pStore->llFreeLocksList);
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// if it does not already exist, allocate a new dynamic lock
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if (*ppLock == NULL)
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{
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*ppLock = GetDynamicReadwriteLock(pStore);
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// if could not get a lock we are in serious trouble
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if (*ppLock == NULL)
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{
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ReleaseListLock(&pStore->llFreeLocksList);
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return ERROR_CAN_NOT_COMPLETE;
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}
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}
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// increment count in the dynamic lock
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(*ppLock)->ulCount++;
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// release the lock for the free locks list
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ReleaseListLock(&pStore->llFreeLocksList);
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// acquire dynamic lock
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if (lmMode == READ_MODE)
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AcquireReadLock(&(*ppLock)->rwlLock);
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else
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AcquireWriteLock(&(*ppLock)->rwlLock);
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return NO_ERROR;
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}
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//----------------------------------------------------------------------------
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// ReleaseDynamicReadwriteLock
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//
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// Locks the FreeLocksList.
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// Releases the dynamic lock.
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// Decrements the count.
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// Free the dynamic lock if count becomes 0.
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// Unlocks the FreeLocksList.
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//----------------------------------------------------------------------------
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VOID
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ReleaseDynamicReadwriteLock (
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PDYNAMIC_READWRITE_LOCK *ppLock,
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LOCK_MODE lmMode,
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PDYNAMIC_LOCKS_STORE pStore
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)
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{
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// acquire the lock for the free locks list
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AcquireListLock(&pStore->llFreeLocksList);
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// release the dynamic readwrite lock
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if (lmMode == READ_MODE)
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ReleaseReadLock(&(*ppLock)->rwlLock);
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else
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ReleaseWriteLock(&(*ppLock)->rwlLock);
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// decrement count in the dynamic lock, free it if count becomes 0
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(*ppLock)->ulCount--;
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if ((*ppLock)->ulCount is 0)
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{
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FreeDynamicReadwriteLock(*ppLock, pStore);
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*ppLock = NULL; // so it is known that it doesn't exist
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}
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// release the lock for the free locks list
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ReleaseListLock(&pStore->llFreeLocksList);
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return;
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}
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#endif
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