Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / QueryOpeningEnumerator.cs / 1305376 / QueryOpeningEnumerator.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // QueryOpeningEnumerator.cs // //[....] // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections; using System.Collections.Generic; using System.Threading; using System.Diagnostics.Contracts; namespace System.Linq.Parallel { ////// A wrapper enumerator that just opens the query operator when MoveNext() is called for the /// first time. We use QueryOpeningEnumerator to call QueryOperator.GetOpenedEnumerator() /// lazily because once GetOpenedEnumerator() is called, PLINQ starts precomputing the /// results of the query. /// internal class QueryOpeningEnumerator: IEnumerator { private readonly QueryOperator m_queryOperator; private IEnumerator m_openedQueryEnumerator; private QuerySettings m_querySettings; private readonly ParallelMergeOptions? m_mergeOptions; private readonly bool m_suppressOrderPreservation; private int m_moveNextIteration = 0; private bool m_hasQueryOpeningFailed; // -- Cancellation and Dispose fields-- // Disposal of the queryOpeningEnumerator can trigger internal cancellation and so it is important // that the internal cancellation signal is available both at this level, and deep in query execution // Also, it is useful to track the cause of cancellation so that appropriate exceptions etc can be // throw from the execution managers. // => Both the topLevelDisposeFlag and the topLevelCancellationSignal are defined here, and will be shared // down to QuerySettings and to the QueryTaskGroupStates that are associated with actual task-execution. // => whilst these are the definitions, it is best to consider QuerySettings as the true owner of these. private readonly Shared m_topLevelDisposedFlag = new Shared (false); //a shared so that it can be referenced by others. // a top-level cancellation signal is required so that QueryOpeningEnumerator.Dispose() can tear things down. // This cancellationSignal will be used as the actual internal signal in QueryTaskGroupState. private readonly CancellationTokenSource m_topLevelCancellationTokenSource = new CancellationTokenSource(); internal QueryOpeningEnumerator(QueryOperator queryOperator, ParallelMergeOptions? mergeOptions, bool suppressOrderPreservation) { Contract.Assert(queryOperator != null); m_queryOperator = queryOperator; m_mergeOptions = mergeOptions; m_suppressOrderPreservation = suppressOrderPreservation; } public TOutput Current { get { if (m_openedQueryEnumerator == null) { throw new InvalidOperationException(SR.GetString(SR.PLINQ_CommonEnumerator_Current_NotStarted)); } return m_openedQueryEnumerator.Current; } } public void Dispose() { m_topLevelDisposedFlag.Value = true; m_topLevelCancellationTokenSource.Cancel(); // initiate internal cancellation. if (m_openedQueryEnumerator != null) { m_openedQueryEnumerator.Dispose(); m_querySettings.CleanStateAtQueryEnd(); } QueryLifecycle.LogicalQueryExecutionEnd(m_querySettings.QueryId); } object IEnumerator.Current { get { return ((IEnumerator )this).Current; } } public bool MoveNext() { if (m_topLevelDisposedFlag.Value) { throw new ObjectDisposedException("enumerator", SR.GetString(SR.PLINQ_DisposeRequested)); } //Note: if Dispose has been called on a different thread to the thread that is enumerating, //then there is a ---- where m_openedQueryEnumerator is instantiated but not disposed. //Best practice is that Dispose() should only be called by the owning thread, hence this cannot occur in correct usage scenarios. // Open the query operator if called for the first time. if (m_openedQueryEnumerator == null) { // To keep the MoveNext method body small, the code that executes first time only is in a separate method. // It appears that if the method becomes too large, we observe a performance regression. This may have // to do with method inlining. See bug 706485. OpenQuery(); } bool innerMoveNextResult = m_openedQueryEnumerator.MoveNext(); // This provides cancellation-testing for the consumer-side of the buffers that appears in each scenario: // Non-order-preserving (defaultMergeHelper) // - asynchronous channel (pipelining) // - synchronous channel (stop-and-go) // Order-preserving (orderPreservingMergeHelper) // - internal results buffer. // This moveNext is consuming data out of buffers, hence the inner moveNext is expected to be very fast. // => thus we only test for cancellation per-N-iterations. // NOTE: the cancellation check occurs after performing moveNext in case the cancellation caused no data // to be produced.. We need to ensure that users sees an OCE rather than simply getting no data. (see Bug702254) if ((m_moveNextIteration & CancellationState.POLL_INTERVAL) == 0) { CancellationState.ThrowWithStandardMessageIfCanceled( m_querySettings.CancellationState.ExternalCancellationToken); } m_moveNextIteration++; return innerMoveNextResult; } /// /// Opens the query and initializes m_openedQueryEnumerator and m_querySettings. /// Called from the first MoveNext call. /// private void OpenQuery() { // Avoid opening (and failing) twice.. not only would it be bad to re-enumerate some elements, but // the cancellation/disposed flags are most likely stale. if (m_hasQueryOpeningFailed) throw new InvalidOperationException(SR.GetString(SR.PLINQ_EnumerationPreviouslyFailed)); try { // stuff in appropriate defaults for unspecified options. m_querySettings = m_queryOperator.SpecifiedQuerySettings .WithPerExecutionSettings(m_topLevelCancellationTokenSource, m_topLevelDisposedFlag) .WithDefaults(); QueryLifecycle.LogicalQueryExecutionBegin(m_querySettings.QueryId); m_openedQueryEnumerator = m_queryOperator.GetOpenedEnumerator( m_mergeOptions, m_suppressOrderPreservation, false, m_querySettings); // Now that we have opened the query, and got our hands on a supplied cancellation token // we can perform an early cancellation check so that we will not do any major work if the token is already canceled. CancellationState.ThrowWithStandardMessageIfCanceled(m_querySettings.CancellationState.ExternalCancellationToken); } catch { m_hasQueryOpeningFailed = true; throw; } } public void Reset() { throw new NotSupportedException(); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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