From b12791a169f25a576cd612b2c881dc0c7c5bdeb3 Mon Sep 17 00:00:00 2001
From: chyyuu <yuchen@tsinghua.edu.cn>
Date: Tue, 10 May 2016 09:58:59 +0800
Subject: [PATCH] add user app for philosopher with semaphore, pthread, etc.

---
 .../philosophers-with-semaphore.c             | 63 +++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 related_info/lab7/semaphore_condition/philosophers-with-semaphore.c

diff --git a/related_info/lab7/semaphore_condition/philosophers-with-semaphore.c b/related_info/lab7/semaphore_condition/philosophers-with-semaphore.c
new file mode 100644
index 0000000..f4876b3
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/philosophers-with-semaphore.c
@@ -0,0 +1,63 @@
+/*  Philosophers.c - Demonstrate the semaphore solution to the dining
+    philosophers problem. The Room semaphore is neede to prevent all
+    philosophers from entering the room and grabbing their left most fork
+    at the same time, which would lead to deadlock. The Room sempahore
+    can be enabled by specifying a command line argument.  */
+
+#include <stdio.h>
+#include <pthread.h>
+#include <semaphore.h>
+typedef	enum { False=0, True=1 } bool ;
+
+#define N 5 /* Number of times each philosopher tries to eat */
+#define P 3 /* Number of philosophers */
+
+sem_t Room;
+sem_t Fork[P];
+bool Switch ;
+
+void *tphilosopher(void *ptr) {
+    int i, k = *((int *) ptr);
+    for(i = 1; i <= N; i++) {
+        printf("%*cThink %d %d\n", k*4, ' ', k, i);
+        if(Switch) {
+            sem_wait(&Room) ;
+        }
+        sem_wait(&Fork[k]) ;
+        sem_wait(&Fork[(k+1) % P]) ;
+        printf("%*cEat %d %d\n", k*4, ' ', k, i);
+        sem_post(&Fork[k]) ;
+        sem_post(&Fork[(k+1) % P]) ;
+        if(Switch) {
+            sem_post(&Room) ;
+        }
+    }
+    pthread_exit(0);
+}
+
+int main(int argc, char * argv[]) {
+    int i, targ[P];
+    pthread_t thread[P];
+    sem_init(&Room, 0, P-1);    
+    Switch = (argc > 1); /* Room semaphore on/off */
+    printf("Switch=%s\n",(Switch?"true":"false"));
+    for(i=0;i<P;i++) {
+        sem_init(&Fork[i], 0, 1);    
+    }
+    for(i=0;i<P;i++) {
+        targ[i] = i;
+        pthread_create(&thread[i], NULL, &tphilosopher,(void *) &targ[i]);
+    }
+    for(i=0;i<P;i++) {
+        pthread_join(thread[i], NULL);
+    }
+    for(i=0;i<P;i++) {
+        sem_destroy(&Fork[i]);
+    }
+    sem_destroy(&Room);
+    return 0;
+}
+
+/*  Please note that the checks on the return value of the system calls
+    have been omitted to avoid cluttering the code. However, system calls
+    can and will fail, in which case the results are unpredictable. */