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November 6, 2006 No comments

Using PI API with Visual Basic 6.0

The PI API provides a common programmer interface to PI System information.

The API is two files: PIAPI32.DLL & PILOG32.DLL which are the foundation of PI networking and data functionality
PIAPI32.dll – contains all of the “C” language functions necessary for any of the PI clients (including PI ProcessBook & PI DataLink) or any of PI’s high speed interfaces to interact with PI: reading and writing data, buffering system, informational functions, etc.
PILOG32.dll – contains all of the “C” language functions necessary to connect to PI servers, logon with security, and create and interpret data packets.

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October 7, 2006 No comments

ATL
临界锁

ATL对象多线程访问临界锁的实现

1. 几个临界区类

ATL将Windows临界区封装了一下，即CComCriticalSection和CComAutoCriticalSection类。两者的实现如下(精简)：

class CComCriticalSection
{
public:
   CComCriticalSection()
   { memset(&m_sec, 0, sizeof(CRITICAL_SECTION)); }
   HRESULT Lock()
   { EnterCriticalSection(&m_sec); return S_OK; }
   HRESULT Unlock()
   { LeaveCriticalSection(&m_sec); return S_OK; }
   HRESULT Init()
   {
   InitializeCriticalSection(&m_sec);
   return S_OK;
   }
   HRESULT Term()
   { DeleteCriticalSection(&m_sec); return S_OK; }

   CRITICAL_SECTION m_sec;
};

class CComAutoCriticalSection : public CComCriticalSection
{
public:
   CComAutoCriticalSection()
   { HRESULT hr = CComCriticalSection::Init(); }
   ~CComAutoCriticalSection()
   { CComCriticalSection::Term(); }
private:
   HRESULT Init();
   HRESULT Term();
};

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October 7, 2006 No comments

ATL
C++

ATL引用计数器的实现

COM对象必须在套间中运行。套间分为单线程套间和多线程套间。在单线程套间中，套间保证COM对象实例仅有一个线程可以访问，而在多线程套间中，COM对象实例可同时被多个线程访问。因此，在多线程套间中执行的COM对象必须解决多线程访问的同步和冲突等线程安全相关问题。

引用计数器管理的实现——CComObjectRootEx

ATL使用CComObjectRootEx类来实现对COM对象计数器的管理，因此，所有的基于ATL的COM对象必须从该类继承。CComObjectRootEx类的声明和实现如下（精简）：
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October 6, 2006 No comments

Multi-thread
VC++

VC++多线程下内存操作的优化

许多程序员发现用VC++编写的程序在多处理器的电脑上运行会变得很慢，这种情况多是由于多个线程争用同一个资源引起的。对于用VC++编写的程序，问题出在VC++的内存管理的具体实现上。以下通过对这个问题的解释，提供一个简便的解决方法，使得这种程序在多处理器下避免出现运行瓶颈。这种方法在没有VC++程序的源代码时也能用。
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