Producer and consumer processes

Fork two processes which share a common 4KB area of memory. One process should produce 10 million bytes, the other should consume them.
Hint: use shared memory, include sys/shm.h. Think to what is fork function doing.

SOLUTION

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#include <semaphore.h> #include <sys/shm.h> #include <sys/stat.h> #include <stdio.h> #include <sys/mman.h> #include <unistd.h> #include <stdlib.h> #include <sys/types.h> #include <fcntl.h> /* COMPILE: g++ process.c -lrt */ // mutex to be allocated in shared memory // so that it can be seen by two processes. sem_t * mutex; int mutexSegmentId; // Identifier // A pointer to the shared memory segment char * sharedMemory; int dataSegmentId; // Identifier // Shared index to parse the memory int * pIndex; int indexSegmentId; // Identifier // Shared Posix Semaphores sem_t * fillCount; // Number of filled spaces in the buffer sem_t * emptyCount; // Available spaces in the buffer int sem1SegmentId; // Identifiers int sem2SegmentId; // Elements to be produced const long TO_PRODUCE = 10000000; const long TO_CONSUME = TO_PRODUCE; const int MEMORY_SIZE = 4096; // Producer of bytes void producer (long toProduce) { // Still bytes to be produced while (toProduce >= 0){ char producedByte = '1'; // Wait if full sem_wait( emptyCount); // Waiting mutex sem_wait( mutex); /* Critical section: Produce one byte */ sharedMemory[ *pIndex] = producedByte; *pIndex = *pIndex + 1; // Release the mutex sem_post(mutex); // Increasing the semaphore sem_post( fillCount); toProduce--; } sem_post( fillCount); // The consumer may not finish before the producer. printf("Successfully produced %lu bytes\n", TO_PRODUCE); } // Consumer of bytes LIFO void consumer(long toConsume) { while (toConsume >= 0){ // Still strings to be produced // Wait if empty sem_wait( fillCount); // Waiting the mutex sem_wait(mutex); /* Critical section: Consume one byte */ // Deleting the last byte of the buffer *pIndex = *pIndex - 1; sharedMemory[ *pIndex] = 0; // Release the mutex sem_post( mutex); // Increasing the semaphore sem_post( emptyCount); toConsume--; } printf("Successfully consumed %lu bytes\n", TO_CONSUME); } void allocateSharedMemory(){ // Allocate a shared memory segment to access the mutex mutexSegmentId = shmget( IPC_PRIVATE, sizeof(sem_t), S_IRUSR | S_IWUSR); mutex = ( sem_t *)shmat ( mutexSegmentId, NULL, 0); // Attaching the shared memory segment // Allocate the shared memory segment where bytes will be produced and consumed dataSegmentId = shmget( IPC_PRIVATE, MEMORY_SIZE, S_IRUSR | S_IWUSR); sharedMemory = (char *) shmat( dataSegmentId, NULL, 0); // Attaching the shared memory segment // Allocate a shared memory segment to access the index indexSegmentId = shmget( IPC_PRIVATE, sizeof(int), S_IRUSR | S_IWUSR); pIndex = (int *) shmat( indexSegmentId, NULL, 0); //Allocate a shared memory segment to access the semaphores sem1SegmentId = shmget( IPC_PRIVATE, sizeof(sem_t), S_IRUSR | S_IWUSR); sem2SegmentId = shmget( IPC_PRIVATE, sizeof(sem_t), S_IRUSR | S_IWUSR); fillCount = (sem_t *) shmat( sem1SegmentId, NULL, 0); emptyCount = (sem_t *) shmat( sem2SegmentId, NULL, 0); } void deallocateSharedMemory(){ // Detaching the shared memory segments shmdt(sharedMemory); shmdt(mutex); shmdt(pIndex); shmdt(fillCount); shmdt(emptyCount); // Removing shared memory segments shmctl(dataSegmentId, IPC_RMID, NULL); shmctl(mutexSegmentId, IPC_RMID, NULL); shmctl(indexSegmentId, IPC_RMID, NULL); shmctl(sem1SegmentId, IPC_RMID, NULL); shmctl(sem2SegmentId, IPC_RMID, NULL); } void initializeVariables(){ // Initialize the mutex sem_init(mutex, 1, 1); // Initialize the index *pIndex = 0; /* Initialize the semaphores * Second argument: more than one process will access it * Third argument: initialization value (empty buffer) */ sem_init( fillCount, 1, 0); sem_init( emptyCount, 1, MEMORY_SIZE); } // Writing a file of the specified length containing all 0 void makefile(const char * filename, int length){ // New File FILE * fileToWrite; fileToWrite = fopen( filename,"w"); if( fileToWrite != NULL){ for(int i = 0; i < length; i++){ fputc('0',fileToWrite); } } fclose(fileToWrite); } int main() { allocateSharedMemory(); initializeVariables(); // Forking the two processes int pid = fork(); if (pid < 0) perror("fork failed "); else if (pid == 0){ // child // Starting producing producer(TO_PRODUCE); } else{ // parent // Starting consuming consumer(TO_CONSUME); } deallocateSharedMemory(); return 0; } <textarea/>

Exercise from CS3008