119 lines
2.4 KiB
C
119 lines
2.4 KiB
C
/*++
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Copyright (c) 1996 Microsoft Corporation
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Module Name:
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yield.c
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Abstract:
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This module implements the function to yield execution for one quantum
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to any other runnable thread.
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Author:
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David N. Cutler (davec) 15-Mar-1996
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Environment:
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Kernel mode only.
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Revision History:
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--*/
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#include "ki.h"
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NTSTATUS
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NtYieldExecution (
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VOID
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)
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/*++
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Routine Description:
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This function yields execution to any ready thread for up to one
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quantum.
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Arguments:
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None.
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Return Value:
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None.
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--*/
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{
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KIRQL OldIrql;
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PRKPRCB Prcb;
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KPRIORITY Priority;
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NTSTATUS Status;
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PRKTHREAD Thread;
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//
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// If any other threads are ready, then attempt to yield execution.
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//
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Status = STATUS_NO_YIELD_PERFORMED;
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if (KiReadySummary != 0) {
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//
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// If a thread has not already been selected for execution, then
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// attempt to select another thread for execution.
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//
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Thread = KeGetCurrentThread();
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KiLockDispatcherDatabase(&Thread->WaitIrql);
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Prcb = KeGetCurrentPrcb();
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if (Prcb->NextThread == NULL) {
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Prcb->NextThread = KiFindReadyThread(Thread->NextProcessor, 1);
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}
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//
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// If a new thread has been selected for execution, then switch
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// immediately to the selected thread.
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//
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if (Prcb->NextThread != NULL) {
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//
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// Give the current thread a new quantum, simulate a quantum
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// end, insert the current thread in the appropriate ready list,
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// and switch context to selected thread.
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//
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Thread->Quantum = Thread->ApcState.Process->ThreadQuantum;
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Thread->State = Ready;
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Priority = Thread->Priority;
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if (Priority < LOW_REALTIME_PRIORITY) {
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Priority = Priority - Thread->PriorityDecrement - 1;
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if (Priority < Thread->BasePriority) {
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Priority = Thread->BasePriority;
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}
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Thread->PriorityDecrement = 0;
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}
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Thread->Priority = (SCHAR)Priority;
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InsertTailList(&KiDispatcherReadyListHead[Priority],
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&Thread->WaitListEntry);
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SetMember(Priority, KiReadySummary);
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KiSwapThread();
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Status = STATUS_SUCCESS;
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} else {
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KiUnlockDispatcherDatabase(Thread->WaitIrql);
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}
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}
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return Status;
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}
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