Critical section

lastmod 2021-11-19created 2015-10-043 edits

A critical section (or shared variable region) in parallel computing is the part of code that accesses a shared resource (a data structure or device) that must not be accessed by more than one thread at the same time. A critical section terminates after a specified amount of time. Therefore, if a thread (task or process) wants to enter a critical section, it must wait for the specified time. A synchronization mechanism such as a semaphore is used when a thread enters or leaves a critical section, to guarantee exclusive use of the shared resource.

Comparison of Critical Section functions on Windows and Linux

A Critical Section is used on Windows to designate a critical region that multiple threads cannot access. On Windows, a Critical Section is used only as a user object; on Linux, you can implement it with a Mutex.

Win32 synchronization structures and functions

• CRITICAL_SECTION: Critical section synchronization structure.
• InitializeCriticalSection(): Initializes the critical section synchronization variable.
• DeleteCriticalSection(): Releases the critical section synchronization variable.
• EnterCriticalSection(): Takes ownership of the critical section synchronization variable. If another thread already owns it, enters the waiting state.
• TryEnterCriticalSection(): Takes ownership of the critical section synchronization variable. If another thread already owns it, returns immediately without entering the waiting state.
• LeaveCriticalSection(): Releases ownership of the critical section. Releases it if a thread already owns it.

How to use synchronization objects and functions

Windows

1. Initialize with InitializeCriticalSection().
2. EnterCriticalSection(), TryEnterCriticalSection(), and LeaveCriticalSection() can be used.
3. Release with DeleteCriticalSection().

Linux

1. Initialize the mutex (Mutex) with pthread_mutex_init().
2. pthread_mutex_lock() and pthread_mutex_unlock() can be used.
3. Release with pthread_mutex_destroy().

Simple Win32 C++ critical section class

To make a Linux version, replace only the corresponding functions and change the header file to pthread.h.

class Lock
{
private:
    CRITICAL_SECTION _critical_section;
public:
    Lock() {
        InitializeCriticalSection(&_critical_section);
    }
    virtual ~Lock() {
        DeleteCriticalSection(&_critical_section);
    }
public:
    void lock() {
        EnterCriticalSection(&_critical_section);
    }
    void unlock() {
        LeaveCriticalSection(&_critical_section);
    }
};

See also

• mutex
• pthread

Favorite site

• Wikipedia (en) description of Critical section

MSDN

• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms682530(v=vs.85.aspx CRITICAL_SECTION Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms683472(v=vs.85.aspx InitializeCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms682552(v=vs.85.aspx DeleteCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms682608(v=vs.85.aspx EnterCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms686857(v=vs.85.aspx TryEnterCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms684169(v=vs.85.aspx LeaveCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms683472(v=vs.85.aspx InitializeCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms682608(v=vs.85.aspx EnterCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms686857(v=vs.85.aspx TryEnterCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms684169(v=vs.85.aspx LeaveCriticalSection() Reference]
• [http://msdn.microsoft.com/en-us/library/windows/desktop/ms682552(v=vs.85.aspx DeleteCriticalSection() Reference]