Я работаю над заданием, в котором профессор просит найти решение проблемы диннинг-философа с использованием семафоров.
Вот мой код:
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <semaphore.h>
#define MAX_THINKING_TIME 1500 /* maximum thinking time in milliseconds */
#define MIN_THINKING_TIME 1000 /* minimum thinking time in milliseconds */
#define MAX_EATING_TIME 1000 /* maximum eating time in milliseconds */
#define MIN_EATING_TIME 750 /* minimum eating time in milliseconds */
/*
* Macros to encapsulate the POSIX semaphore functions.
*/
#define semaphore_create(s,v) sem_init( &s, 0, v )
#define semaphore_wait(s) sem_wait( &s )
#define semaphore_signal(s) sem_post( &s )
#define semaphore_release(s) sem_destroy( &s )
typedef sem_t semaphore;
// Each chopstick is represented by a semaphore (shared between all processes).
semaphore *chopstick;
int NUM_PHILOSOPHERS; /* number of philosophers */
int NUM_REPETITIONS; /* number of cycles */
/*
* Generating a random number within a range.
*/
unsigned int randr(unsigned int min, unsigned int max)
{
double scaled = (double)rand()/RAND_MAX;
return (max - min +1) * scaled + min;
}
/*
* To pick up his chopsticks, a philosopher does a semaphore wait on each.
* Alternating order prevents deadlock.
*/
void pickup_chopsticks(int index)
{
if(index % 2 == 0) /* Even number: Left, then right */
{
semaphore_wait(chopstick[(index+1) % NUM_PHILOSOPHERS]);
printf("Philosopher #%d: I am picking up the left chopstick!\n", index+1);
semaphore_wait(chopstick[index]);
printf("Philosopher #%d: I am picking up the right chopstick!\n", index+1);
}
else /* Odd number: Right, then left */
{
semaphore_wait(chopstick[index]);
printf("Philosopher #%d: I am picking up the right chopstick!\n", index+1);
semaphore_wait(chopstick[(index+1) % NUM_PHILOSOPHERS]);
printf("Philosopher #%d: I am picking up the left chopstick!\n", index+1);
}
}
/*
* To drop his chopsticks, a philosopher does a semaphore signal on each.
* Order does not matter.
*/
void drop_chopsticks(int index)
{
printf("Philosopher #%d: I am dropping the right chopstick!\n", index+1);
semaphore_signal(chopstick[index]);
printf("Philosopher #%d: I am dropping the left chopstick!\n", index+1);
semaphore_signal(chopstick[(index+1) % NUM_PHILOSOPHERS]);
}
/*
* Simulate a philosopher - endlessly cycling between eating and thinking
* until his "life" is over.
*/
void start_philosopher(int index)
{
int i; // A counter.
for(i = 0; i < NUM_REPETITIONS; i++)
{
/* Hungry */
printf("Philosopher #%d (Cycle #%d): I am hungry!\n", index+1, i+1);
pickup_chopsticks(index);
/* Eating */
printf("Philosopher #%d (Cycle #%d): I am eating!\n", index+1, i+1);
usleep(1000 * randr(MIN_EATING_TIME, MAX_EATING_TIME));
drop_chopsticks(index);
/* Thinking */
printf("Philosopher #%d (Cycle #%d): I am thinking!\n", index+1, i+1);
usleep(1000 * randr(MIN_THINKING_TIME, MAX_THINKING_TIME));
}
printf("Philosopher #%d: I am dead!\n", index+1);
exit(0);
}
/*
* The main function.
*/
int main(int argc, char *argv[])
{
// If the input arguments are not 2 elements, display a message and return.
if(argc != 3)
{
printf("You have to insert arguments in the form:\n");
printf("Number_of_Philosopher Number_of_repeats\n");
return -1;
}
// Set value of NUM_PHILOSOPHERS and NUM_REPETITIONS from the user input.
NUM_PHILOSOPHERS = atoi(argv[1]);
NUM_REPETITIONS = atoi(argv[2]);
int i; // A counter.
// Allocate memory for the semaphores.
chopstick = malloc(NUM_PHILOSOPHERS * sizeof(semaphore));
// Create semaphores to represent "one user at a time" chopsticks.
for(i = 0; i < NUM_PHILOSOPHERS; i++)
semaphore_create(chopstick[i], 1);
// Create n processes for n philosophers
for(i = 0; i < NUM_PHILOSOPHERS; i++)
{
if(fork() == 0) start_philosopher(i);
else wait();
}
// Release semaphore resources.
for(i = 0; i < NUM_PHILOSOPHERS; i++)
semaphore_release(chopstick[i]);
// Free the memory.
free(chopstick);
return 0;
}
и когда я запускаю его, я получаю следующее:
$ ./run 2 2
Philosopher #1 (Cycle #1): I am hungry!
Philosopher #1: I am picking up the left chopstick!
Philosopher #1: I am picking up the right chopstick!
Philosopher #1 (Cycle #1): I am eating!
Philosopher #1: I am dropping the right chopstick!
Philosopher #1: I am dropping the left chopstick!
Philosopher #1 (Cycle #1): I am thinking!
Philosopher #1 (Cycle #2): I am hungry!
Philosopher #1: I am picking up the left chopstick!
Philosopher #1: I am picking up the right chopstick!
Philosopher #1 (Cycle #2): I am eating!
Philosopher #1: I am dropping the right chopstick!
Philosopher #1: I am dropping the left chopstick!
Philosopher #1 (Cycle #2): I am thinking!
Philosopher #1: I am dead!
Philosopher #2 (Cycle #1): I am hungry!
^Z
[6]+ Stopped ./run 2 2
Как видите, у меня две проблемы:
- Процесс n + 1 не выполняется, если не выполнен процесс n.
- В предыдущем тесте запуска программы она застревала, когда второй философ просит поднять палочки для еды. Кажется, что семафор не передан, и философ ждет сигнала.
Не могли бы вы помочь мне исправить программу?