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#COMPILING SEMAPHOR C CODE#
Program 7.5 Program code for the semaphore class. As shown, the code is bare boneslittle is done to handle errors, and only basic semaphore functionality is addressed. The C++ code that implements the semaphore class is found in the program file SSemaphore.cxx (Program 7.5). Get returns the current value of a semaphore.
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This method tests whether or not the semaphore is at 0. This method atomically tests and decrements the semaphore. This method removes the semaphore from the system if the calling function is the process that generated the semaphore. Additionally, it generates the private, single element semaphore and sets it to 0. This method assigns the proper values to the zero, lock, and unlock sembuf structures and saves the PID of the calling process. The functionality of each method is shown in Table 7.10. There are seven public methods and six private data members in the class. Struct sembuf zero,lock, unlock // hoo ha's for P,V & Z operationsĪs defined, the SSemaphore class creates a private semaphore set with a single element. Struct seminfo *_buf // buffer for IPC_INFO Unsigned short int *array // array for GETALL, SETALL Struct semid_ds *buf // buffer for IPC_STAT, IPC_SET #if defined(_GNU_LIBRARY_) & !defined(_SEM_SEMUN_UNDEFINED) Int Get( ) // Return value of the semaphore So you need compile semaphore.c like this: 1 gcc semaphore.c -pthreaad -o semaphore Copied Function Description semopen Opens/creates a named semaphore for use by a process semwait lock a semaphore sempost unlock a semaphore semclose Deallocates the specified named semaphore semunlink Removes a specified named semaphore 1 /semaphore.
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Void Put( const int ) // Assign a value to semaphore Int Z( ) // WAIT while semaphore is NOT 0 Void V( ) // UNLOCK (increment semaphore) ~SSemaphore( ) // Destructor - remove semaphoreģ0 int P( ) // LOCK (decrement semaphore) Grayġ - Semaphore allocation failure 2 - Unable remove semaphoreģ - Unable to LOCK semaphore 4 - Unable to UNLOCK semaphoreġ0 5 - Failure on wait for ZERO 6 - Unable to assign value
#COMPILING SEMAPHOR C HOW TO#
See the text for instructions on how to use The name SSemaphore (with the extra 'S' ) was chosen to minimize any conflicts with existing semaphore definitions.įigure 7.10 Header file for a basic semaphore class.Ī VERY simplified semaphore class for use in a std UNIXĮnvironment. A declaration of a simplified semaphore class called SSemaphore is shown in Figure 7.10. A semaphore class would define the relationships between semaphore data and the functions ( methods ) that manipulate this data.
#COMPILING SEMAPHOR C FREE#
The only thing is to make sure that all philosophers are entering the room, performing the eating operation and leaving the room and also that no two philosophers are using the same chopstick at the same time.ĭo let me know if you face any problems and feel free to leave a feedback.As with message queues, the syntax and manipulation of semaphores is somewhat complex, making them a prime candidate for incorporation into a C++ class. It can be different on different machines. A useful way to think of a semaphore as used in a real-world system is as a record of how many units of a particular resource are available. A trivial semaphore is a plain variable that is changed (for example, incremented or decremented, or toggled) depending on programmer-defined conditions. So, this is how we can implement the solution to the dining philosophers problem using semaphores.Īt the end, you should get an output which looks like this: Philosopher 4 has entered room Philosopher 4 is eating Philosopher 2 has entered room Philosopher 2 is eating Philosopher 3 has entered room Philosopher 1 has entered room Philosopher 2 has finished eating Philosopher 4 has finished eating Philosopher 3 is eating Philosopher 1 is eating Philosopher 0 has entered room Philosopher 3 has finished eating Philosopher 1 has finished eating Philosopher 0 is eating Philosopher 0 has finished eating Semaphores are a type of synchronization primitive. The same thing happens for all 5 philosophers.Īfter all the 5 are done, we join the threads back to the main process.
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sem_post(&chopstick) sem_post(&chopstick) sem_post(&room) Using the above functions, we free all the semaphores so that they can be used by other threads. Here’s the program: #include #include #include #include #include sem_t room sem_t chopstick void * philosopher(void *) void eat(int) int main() Here, I am going to explain the solution to this problem using the concept of semaphores in C.