Critical Section - Application Level Critical Sections

Application Level Critical Sections

Application-level critical sections reside in the memory range of the process and are usually modifiable by the process itself. This is called a user-space object because the program run by the user (as opposed to the kernel) can modify and interact with the object. However, the functions called may jump to kernel-space code to register the user-space object with the kernel.

Example Code For Critical Sections with POSIX pthread library

/* Sample C/C++, Unix/Linux */ #include /* This is the critical section object (statically allocated). */ static pthread_mutex_t cs_mutex = PTHREAD_MUTEX_INITIALIZER; void f { /* Enter the critical section -- other threads are locked out */ pthread_mutex_lock( &cs_mutex ); /* Do some thread-safe processing! */ /*Leave the critical section -- other threads can now pthread_mutex_lock */ pthread_mutex_unlock( &cs_mutex ); } int main { f; return 0; }

Example Code For Critical Sections with Win32 API

/* Sample C/C++, Windows, link to kernel32.dll */ #include static CRITICAL_SECTION cs; /* This is the critical section object -- once initialized, it cannot be moved in memory */ /* If you program in OOP, declare this as a non-static member in your class */ void f { /* Enter the critical section -- other threads are locked out */ EnterCriticalSection(&cs); /* Do some thread-safe processing! */ /* Leave the critical section -- other threads can now EnterCriticalSection */ LeaveCriticalSection(&cs); } int main { /* Initialize the critical section before entering multi-threaded context. */ InitializeCriticalSection(&cs); f; /* Release system object when all finished -- usually at the end of the cleanup code */ DeleteCriticalSection(&cs); return 0; }

Note that on Windows NT (not 9x/ME), the function TryEnterCriticalSection can be used to attempt to enter the critical section. This function returns immediately so that the thread can do other things if it fails to enter the critical section (usually due to another thread having locked it). With the pthreads library, the equivalent function is pthread_mutex_trylock. Note that the use of a CriticalSection is not the same as a Win32 Mutex, which is an object used for inter-process synchronization. A Win32 CriticalSection is for intra-process synchronization (and is much faster regarding lock times), however it cannot be shared across processes.

Read more about this topic:  Critical Section

Famous quotes containing the words application, level, critical and/or sections:

    “We will not be imposed upon by this vast application of forces. We believe that most things will have to be accomplished still by the application called Industry. We are rather pleased, after all, to consider the small private, but both constant and accumulated, force which stands behind every spade in the field. This it is that makes the valleys shine, and the deserts really bloom.”
    —Henry David Thoreau (1817–1862)

    “One of the peculiar sins of the twentieth century which we’ve developed to a very high level is the sin of credulity. It has been said that when human beings stop believing in God they believe in nothing. The truth is much worse: they believe in anything.”
    —Malcolm Muggeridge (1903–1990)

    “A third variety of drama ... begins as tragedy with scraps of fun in it ... and ends in comedy without mirth in it, the place of mirth being taken by a more or less bitter and critical irony.”
    —George Bernard Shaw (1856–1950)

    “... many of the things which we deplore, the prevalence of tuberculosis, the mounting record of crime in certain sections of the country, are not due just to lack of education and to physical differences, but are due in great part to the basic fact of segregation which we have set up in this country and which warps and twists the lives not only of our Negro population, but sometimes of foreign born or even of religious groups.”
    —Eleanor Roosevelt (1884–1962)