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Re-Entrant Custom Critical Section

, 14 Nov 2010
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Re-Entrant code


The motivation to write this article came from Dr.Sai's excellent article "Working with CRITICAL_SECTION", so before reading this article one should first review that article.

This article explains how we can extend the custom critical section architecture to make it re-entrant.


Enter Part

void MyCriticalSection::Enter()

To make it re-entrant we need to have a variable to save the recursion count, m_lRecursionCount. The recursion count is local to the thread, is incremented each time that EnterCriticalSection is called and keeps count of the number of times that EnterCriticalSection is called in the thread.

In the above scenario, the expression if (m_ThreadID == GetCurrentThreadId()) will evalute to TRUE and increment the recursion count. Prior to that, m_threadID is made equal to GetCurrentThreadId() once either interlockedincrement(&count) == 0 or waitforsingleobject succeeds.

Leave Part

void MyCriticalSection::Leave()

The expression if (m_ThreadID != GetCurrentThreadId()) is necessary so that no other thread makes a call to Leave() without making a call to Enter(), in which case the call to Leave should be ignored.

First a check of m_lrecursivecount == 0 is made. If the recursion count is not zero, the recursion count is decremented, which means the thread needs to call Leave some additional times before relinquishing control to other waiting threads.

If the statement m_lrecursivecount == 0 evaluates to TRUE, then we need to decrement the count and make a call to SetEvent. Before making a call to SetEvent we need to check that InterlockedDecrement(&count) > 0. If TRUE, a call to SetEvent is made; if FALSE, it is the last thread and hence there is no need to call SetEvent.


One should step through this program and examine every step until satisfied that it does work.

Finally thanks to Dr.Sai's article for helping me open the petals of knowledge. I am hoping for his comments on this article.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Bharath NS
Software Developer (Senior) IBM
India India
No Biography provided

Comments and Discussions

QuestionWin32 CriticalSection is far faster PinmemberXarium29-Mar-12 14:40 
GeneralWindows via C/C++ (Richter) PinmemberFrankLaPiana22-Nov-10 11:46 
GeneralInteresting re-entrance problem. PinmemberXanblax26-Sep-07 5:20 
Question¿Time-out capabilities? PinmemberXanblax24-Sep-07 23:22 
GeneralDoes not work! Pinmembersreskovi19-Sep-07 4:05 
GeneralRe: Does not work! PinmemberXanblax25-Sep-07 22:07 
GeneralRe: Does not work! PinmemberBharath NS10-Oct-07 20:50 
GeneralPlease vote my Article Pinmembersanthosh4gCode20-Feb-11 3:40 
GeneralDr.Sai's Comments PinmemberDr. Sai25-Oct-06 0:30 

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