BOOL ConsumeElement(int nThreadNum, int nRequestNum, HWND hWndLB) {
// Get access to the queue to consume a new element
AcquireSRWLockShared(&g_srwLock);
// Fall asleep until there is something to read.
// Check if, while it was asleep,
// it was not decided that the thread should stop
while (g_q.IsEmpty(nThreadNum) && !g_fShutdown) {
// There was not a readable element
AddText(hWndLB, TEXT("[%d] Nothing to process"), nThreadNum);
// The queue is empty
// --> Wait until a writer adds a new element to read
// and come back with the lock acquired in shared mode
SleepConditionVariableSRW(&g_cvReadyToConsume, &g_srwLock,
INFINITE, CONDITION_VARIABLE_LOCKMODE_SHARED);
}
// When thread is exiting, the lock should be released for writer
// and readers should be signaled through the condition variable
if (g_fShutdown) {
// Show that the current thread is exiting
AddText(hWndLB, TEXT("[%d] bye bye"), nThreadNum);
// Another writer thread might still be blocked on the lock
// --> release it before exiting
ReleaseSRWLockShared(&g_srwLock);
// Notify other readers that it is time to exit
// --> release readers
WakeConditionVariable(&g_cvReadyToConsume);
return(FALSE);
}
// Get the first new element
CQueue::ELEMENT e;
// Note: No need to test the return value since IsEmpty
// returned FALSE
g_q.GetNewElement(nThreadNum, e);
// No need to keep the lock any longer
ReleaseSRWLockShared(&g_srwLock);
// Show result of consuming the element
AddText(hWndLB, TEXT("[%d] Processing %d:%d"),
nThreadNum, e.m_nThreadNum, e.m_nRequestNum);
// A free slot is now available for writer threads to produce
// --> wake up a writer thread
WakeConditionVariable(&g_cvReadyToProduce);
return(TRUE);
}
