195 lines
4.6 KiB
C++
195 lines
4.6 KiB
C++
/*===================================================================
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Microsoft Denali
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Microsoft Confidential.
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Copyright 1997 Microsoft Corporation. All Rights Reserved.
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Component: ID Generator
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File: Idgener.cpp
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Owner: DmitryR
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This is the ID Generator source file.
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===================================================================*/
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#include "denpre.h"
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#pragma hdrstop
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#include "Idgener.h"
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#include "memchk.h"
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/*===================================================================
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CIdGenerator::CIdGenerator
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NOTE: Constructor
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Parameters:
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Returns:
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===================================================================*/
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CIdGenerator::CIdGenerator()
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: m_fInited(FALSE),
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m_dwStartId(0),
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m_dwLastId(0)
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{
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}
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/*===================================================================
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CIdGenerator::~CIdGenerator()
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NOTE: Destructor
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Parameters:
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Returns:
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===================================================================*/
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CIdGenerator::~CIdGenerator()
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{
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if ( m_fInited )
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DeleteCriticalSection( &m_csLock );
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}
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/*===================================================================
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HRESULT CIdGenerator::Init()
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NOTE: Seed new starting Id
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Parameters:
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Returns: HRESULT (could fail to create critical section)
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===================================================================*/
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HRESULT CIdGenerator::Init()
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{
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Assert(!m_fInited);
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/*===
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Seed the starting id
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The starting Id should be:
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1) random
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2) not to close to recently generated starting ids
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To accomplish the above, starting Id is in the
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following (binary) format:
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00TT.TTTT TTTT.TTTT TTT1.RRRR RRRR.RRRR
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RRR is random number to introduce some
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randomness
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1 is needed to make sure the id is far
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enough from 0
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TTT is current time() in 4 second increments.
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This means that 4 second in server restart
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delay translates into 8,192 difference in
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the starting Id (122880 sessions / minute).
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17 bits of 4 sec intervals make a roll over
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time of about 145 hours, hopefully longer
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than a client's connection lifetime (not
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that it REALLY matters).
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00 in the highest bits is to make sure it
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doesn't reach 0xffffffff too soon
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===*/
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DWORD dwRRR = rand() & 0x00000FFF;
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DWORD dwTTT = (((DWORD)time(NULL)) >> 2) & 0x0001FFFF;
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m_dwStartId = (dwTTT << 13) | (1 << 12) | dwRRR;
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m_dwLastId = m_dwStartId;
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HRESULT hr = S_OK;
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ErrInitCriticalSection( &m_csLock, hr );
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if ( FAILED( hr ) )
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return hr;
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m_fInited = TRUE;
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return S_OK;
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}
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/*===================================================================
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HRESULT CIdGenerator::Init(CIdGenerator StartId)
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NOTE: Seed new starting Id with Id passed in
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Parameters:
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Returns: HRESULT (could fail to create critical section)
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===================================================================*/
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HRESULT CIdGenerator::Init(CIdGenerator & StartId)
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{
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Assert(!m_fInited);
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m_dwStartId = StartId.m_dwStartId;
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m_dwLastId = m_dwStartId;
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HRESULT hr = NOERROR;
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ErrInitCriticalSection( &m_csLock, hr );
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if ( FAILED( hr ) )
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return hr;
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m_fInited = TRUE;
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return NOERROR;
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}
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/*===================================================================
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DWORD CIdGenerator::NewId()
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NOTE: Generates new ID
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Parameters:
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Returns: generated ID
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===================================================================*/
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DWORD CIdGenerator::NewId()
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{
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Assert(m_fInited);
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DWORD dwId;
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EnterCriticalSection(&m_csLock);
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dwId = ++m_dwLastId;
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LeaveCriticalSection(&m_csLock);
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if (dwId == INVALID_ID)
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{
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// doesn't happen very often do critical section again
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// to make the above critical section shorter
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EnterCriticalSection(&m_csLock);
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// check again in case other thread changed it
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if (m_dwLastId == INVALID_ID)
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m_dwLastId = m_dwStartId; // roll over
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m_dwLastId++;
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LeaveCriticalSection(&m_csLock);
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dwId = m_dwLastId;
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}
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return dwId;
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}
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/*===================================================================
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BOOL CIdGenerator::IsValidId(DWORD dwId)
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NOTE: Checks if the given Id is valid (with start-last range)
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Parameters:
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DWORD dwId Id value to check
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Returns: generated ID
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===================================================================*/
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BOOL CIdGenerator::IsValidId
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(
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DWORD dwId
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)
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{
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Assert(m_fInited);
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return (dwId > m_dwStartId && dwId <= m_dwLastId);
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}
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