LogLogRecordEnumerator.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / cdf / src / WCF / Log / System / IO / Log / LogLogRecordEnumerator.cs / 1305376 / LogLogRecordEnumerator.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------------------------
namespace System.IO.Log
{ 
    using System;
    using System.Collections; 
    using System.Collections.Generic; 
    using System.Runtime.InteropServices;
 

    // Although we would normally not make an enumerator like this
    // thread-safe, we do so because we are dealing in unmanaged
    // memory. Specifically, we construct an UnmanagedMemoryStream 
    // around a pointer that comes back from ReadLogRecord and
    // ReadNextLogRecord (in LogLogRecord). This is fine, so long as 
    // we know that memory is valid. That memory is valid as long as 
    // the read context is valid. When the read context moves on, or
    // becomes invalid, we must "detach" the current record, copying 
    // the data into a managed array.
    //
    // Of necessity, we allocate the read context before the record,
    // and detach the record before freeing or moving the read 
    // context. What if some malicious person engineered a ----
    // condition between the allocate/move and the detach? In this 
    // case, a log record might wind up un-detached, but pointing at 
    // invalid memory. This is NOT GOOD. Hence the thread-safety.
    // 
    class LogLogRecordEnumerator : IEnumerator
    {
        enum State
        { 
            BeforeFirst,
            Valid, 
            AfterLast, 
            Disposed
        } 

        LogRecordSequence recordSequence;
        CLFS_CONTEXT_MODE mode;
        ulong             startLsn; 

        State             state; 
        object            syncRoot; 
        SafeReadContext   readContext;
        LogLogRecord      current; 

        internal LogLogRecordEnumerator(LogRecordSequence recordSequence,
                                        CLFS_CONTEXT_MODE mode,
                                        ulong startLsn) 
        {
            this.recordSequence = recordSequence; 
            this.mode = mode; 
            this.startLsn = startLsn;
 
            this.syncRoot = new object();
            this.state = State.BeforeFirst;
        }
 
        object IEnumerator.Current
        { 
            get 
            {
                return this.Current; 
            }
        }

        public LogRecord Current 
        {
            get 
            { 
                lock(this.syncRoot)
                { 
                    if (this.state == State.Disposed)
#pragma warning suppress 56503
                         throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed());
 
// IEnumerable interface contract for "current" member can throw InvalidOperationException. Suppressing this warning.
 
                    if (this.state == State.BeforeFirst) 
#pragma warning suppress 56503
                     throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.EnumNotStarted()); 
                    if (this.state == State.AfterLast)
#pragma warning suppress 56503
                         throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.EnumEnded());
 
                    return this.current;
                } 
            } 
        }
 
        public void Dispose()
        {
            lock(this.syncRoot)
            { 
                if (this.current != null)
                { 
                    this.current.Detach(); 
                    this.current = null;
                } 

                if ((this.readContext != null) &&
                    (!this.readContext.IsInvalid))
                { 
                    this.readContext.Close();
                } 
 
                this.state = State.Disposed;
            } 
        }

        public bool MoveNext()
        { 
            lock(this.syncRoot)
            { 
                if (this.state == State.Disposed) 
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed());
                if (this.state == State.AfterLast) 
                    return false;

                if (this.readContext == null)
                { 
                    return ReadLogRecord();
                } 
                else 
                {
                    if (this.current != null) 
                        this.current.Detach();

                    return ReadNextLogRecord();
                } 
            }
        } 
 
        bool ReadLogRecord()
        { 
            if (!((this.readContext == null || this.readContext.IsInvalid) && (this.current == null)))
            {
                // An internal consistency check has failed. The indicates a bug in IO.Log's internal processing
                // Rather than proceeding with non-deterministic execution and risking the loss or corruption of 
                // log records, we failfast the process.
                DiagnosticUtility.FailFast("Should only call this for first record!"); 
            } 
            unsafe
            { 
                byte *readBuffer;
                int bufferLength;
                byte recordType;
                ulong lsnUser; 
                ulong lsnPrevious;
 
                if (!UnsafeNativeMethods.ReadLogRecordSync( 
                        this.recordSequence.MarshalContext,
                        ref this.startLsn, 
                        this.mode,
                        out readBuffer,
                        out bufferLength,
                        out recordType, 
                        out lsnUser,
                        out lsnPrevious, 
                        out this.readContext)) 
                {
                    this.state = State.AfterLast; 
                    return false;
                }

                if ((recordType & Const.ClfsDataRecord) != 0) 
                {
                    this.current = new LogLogRecord( 
                        new SequenceNumber(this.startLsn), 
                        new SequenceNumber(lsnUser),
                        new SequenceNumber(lsnPrevious), 
                        readBuffer,
                        bufferLength);

                    this.state = State.Valid; 
                    return true;
                } 
                else 
                {
                    return ReadNextLogRecord(); 
                }
            }
        }
 
        bool ReadNextLogRecord()
        { 
            if (this.readContext == null || this.readContext.IsInvalid) 
            {
                // An internal consistency check has failed. The indicates a bug in IO.Log's internal processing 
                // Rather than proceeding with non-deterministic execution and risking the loss or corruption of
                // log records, we failfast the process.
                DiagnosticUtility.FailFast("Should only be called for records after the first!");
            } 
            unsafe
            { 
                byte *readBuffer; 
                int bufferLength;
                byte recordType = Const.ClfsDataRecord; 
                ulong lsnUser;
                ulong lsnPrevious;
                ulong lsnRecord;
 
                if (!UnsafeNativeMethods.ReadNextLogRecordSync(
                        this.readContext, 
                        out readBuffer, 
                        out bufferLength,
                        ref recordType, 
                        out lsnUser,
                        out lsnPrevious,
                        out lsnRecord))
                { 
                    this.state = State.AfterLast;
                    return false; 
                } 

                this.current = new LogLogRecord( 
                    new SequenceNumber(lsnRecord),
                    new SequenceNumber(lsnUser),
                    new SequenceNumber(lsnPrevious),
                    readBuffer, 
                    bufferLength);
 
                this.state = State.Valid; 
                return true;
            } 
        }

        public void Reset()
        { 
            lock (this.syncRoot)
            { 
                if (this.state == State.Disposed) 
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed());
 
                if (this.current != null)
                {
                    this.current.Detach();
                    this.current = null; 
                }
 
                if ((this.readContext != null) && 
                    (!this.readContext.IsInvalid))
                { 
                    this.readContext.Close();
                    this.readContext = null;
                }
 
                this.state = State.BeforeFirst;
            } 
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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LogLogRecordEnumerator.cs source code in C# .NET

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