哲学家问题观察死锁

1.1 不死锁代码

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <pthread.h>
#include <errno.h>
#include <math.h>

// chopstick as mutex
pthread_mutex_t chopstick[6];
void *eat_think(void *arg)
{
	char phi = *(char *)arg;
	int left, right;
	switch(phi) {
	case 'A':
		left = 5;
		right = 1;
		break;
	case 'B':
		left = 1;
		right = 2;
		break;
	case 'C':
		left = 2;
		right = 3;
		break;
	case 'D':
		left = 3;
		right = 4;
		break;
	case 'E':
		left = 4;
		right = 5;
		break;
	}
	int j;
	for (j = 0; j < 5; j++)
	{
		usleep(3);
		pthread_mutex_lock(&chopstick[left]);
		printf("Philosopher %c fetches chopstick %d\n", phi, left);

		if (pthread_mutex_trylock(&chopstick[right]) == EBUSY)
		{
			pthread_mutex_unlock(&chopstick[left]);
			continue;
		}

		// pthread_mutex_lock(&chopstick[right]);
		printf("Philosopher %c fetches chopstick %d\n", phi, right);
		printf("philosopher %c is eating.  %d\n", phi, j+1);
		usleep(3);
		pthread_mutex_unlock(&chopstick[left]);
		printf("philosopher %c release chopstick %d\n", phi, left);
		pthread_mutex_unlock(&chopstick[right]);
		printf("Philosopher %c release chopstick %d\n", phi, right);
	}
}

int main()
{
	pthread_t A, B, C, D, E;
	int i;
	for(i = 0; i < 5; i++)
	{
		pthread_mutex_init(&chopstick[i], NULL);
	}
	pthread_create(&A, NULL, eat_think, "A");
	pthread_create(&B, NULL, eat_think, "B");
	pthread_create(&C, NULL, eat_think, "C");
	pthread_create(&D, NULL, eat_think, "D");
	pthread_create(&E, NULL, eat_think, "E");

	pthread_join(A, NULL);
	pthread_join(B, NULL);
	pthread_join(C, NULL);
	pthread_join(D, NULL);
	pthread_join(E, NULL);
	return 0;
}

1.2 不死锁截图

2.1 死锁代码

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <pthread.h>
#include <errno.h>
#include <math.h>

// chopstick as mutex
pthread_mutex_t chopstick[6];
void *eat_think(void *arg)
{
	char phi = *(char *)arg;
	int left, right;
	switch(phi) {
	case 'A':
		left = 5;
		right = 1;
		break;
	case 'B':
		left = 1;
		right = 2;
		break;
	case 'C':
		left = 2;
		right = 3;
		break;
	case 'D':
		left = 3;
		right = 4;
		break;
	case 'E':
		left = 4;
		right = 5;
		break;
	}
	int j;
	for (j = 0; j < 500; j++)
	{
		usleep(3);
		pthread_mutex_lock(&chopstick[left]);
		printf("Philosopher %c fetches chopstick %d\n", phi, left);

		// if (pthread_mutex_trylock(&chopstick[right] == EBUSY))
		// {
		//	pthread_mutex_unlock(&chopstick[left]);
		//	continue;
		// }

		pthread_mutex_lock(&chopstick[right]);
		printf("Philosopher %c fetches chopstick %d\n", phi, right);
		printf("philosopher %c is eating.  %d\n", phi, j+1);
		usleep(3);
		pthread_mutex_unlock(&chopstick[left]);
		printf("philosopher %c release chopstick %d\n", phi, left);
		pthread_mutex_unlock(&chopstick[right]);
		printf("Philosopher %c release chopstick %d\n", phi, right);
	}
}

int main()
{
	pthread_t A, B, C, D, E;
	int i;
	for(i = 0; i < 5; i++)
	{
		pthread_mutex_init(&chopstick[i], NULL);
	}
	pthread_create(&A, NULL, eat_think, "A");
	pthread_create(&B, NULL, eat_think, "B");
	pthread_create(&C, NULL, eat_think, "C");
	pthread_create(&D, NULL, eat_think, "D");
	pthread_create(&E, NULL, eat_think, "E");

	pthread_join(A, NULL);
	pthread_join(B, NULL);
	pthread_join(C, NULL);
	pthread_join(D, NULL);
	pthread_join(E, NULL);
	return 0;
}

2.2 死锁截图