Strings producer and consumer processes

Fork two processes that create and remove 10,000 random length strings of random alphabetic characters.
Hint: use shared memory, include sys/shm.h.
See also Producer and consumer processes

SOLUTION

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#include <semaphore.h> #include <sys/shm.h> #include <sys/stat.h> #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <sys/types.h> #include <fcntl.h> #include <math.h> #include <string.h> #include <sys/mman.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, it points to the first free byte 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; const int BUFFER_SIZE = 50; // Number of storable strings in the buffer const long TO_PRODUCE = 10000; // Strings to be produced const long TO_CONSUME = TO_PRODUCE; // Strings to be consumed const int MAX_STRING_LENGTH = 20; // Strings' maximum length // Returning a random alphabetic character char randomChar(){ return 'a' + rand() % ('z'-'a'); } // Returning a random length string, with random characters char * randomString(){ int dim = rand() % MAX_STRING_LENGTH; char * res = (char *) malloc( sizeof(char) * ( dim + 1)); int i; for( i = 0; i < dim; i++){ res[i] = randomChar(); } res[i] = '\0'; return res; } // Producer of strings void producer (long toProduce){ // Still strings to be produced while (toProduce >= 0){ // Wait if full sem_wait( emptyCount); // Waiting mutex sem_wait( mutex); /* Critical section: Producing one string */ char * toWrite = randomString(); // String to be stored strcpy( sharedMemory + *pIndex, toWrite); *pIndex = *pIndex + strlen(toWrite) + 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("finish prod\n"); } // Returning the length of the previous string stored in the buffer int previousStrLen(char * str, int index){ if(index < 0) return 1; else { if( str[index] == '\0') return 1; else return 1 + previousStrLen(str, index - 1); } } // From the pointer str, deleting num characters void deleteNextCharacters(char * str, int num){ for(int i = 0; i < num; i++){ str[ i]= 0; // Null } } // Consumer of strings LIFO void consumer(long toConsume, char * result){ // Still strings to be consumed while (toConsume >= 0){ // Wait if empty sem_wait( fillCount); // Waiting the mutex sem_wait(mutex); /* Critical section: Consume one string */ // Length of the previous string int prevLength = previousStrLen(sharedMemory, (*pIndex)-2); *pIndex = (*pIndex) - prevLength; // Deleting the last string in the buffer deleteNextCharacters( sharedMemory + *pIndex, prevLength); // Release the mutex sem_post( mutex); // Increasing the semaphore sem_post( emptyCount); toConsume--; } printf("finish cons\n"); } 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 strings will be produced and consumed dataSegmentId = shmget( IPC_PRIVATE, BUFFER_SIZE * (MAX_STRING_LENGTH * sizeof(char)), 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, BUFFER_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 producer(TO_PRODUCE); } else{ // parent consumer(TO_CONSUME); } deallocateSharedMemory(); return 0; } <textarea/> <br /> Exercise from <a href="http://www.csd.abdn.ac.uk/~jrl/teach/CS3008/base.htm" target="_blank">CS3008</a> <strong><span style="font-size: large;"><br /></span></strong>

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