From dbc1819174f33088b905f824494f4a68e1a293e8 Mon Sep 17 00:00:00 2001
From: chyyuu <yuchen@tsinghua.edu.cn>
Date: Tue, 10 May 2016 10:04:03 +0800
Subject: [PATCH] update comments for check_sync.c in lab7&lab7_result

---
 labcodes/lab7/kern/sync/check_sync.c               | 60 ++++++++++++++++++++++
 labcodes_answer/lab7_result/kern/sync/check_sync.c |  2 +-
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/labcodes/lab7/kern/sync/check_sync.c b/labcodes/lab7/kern/sync/check_sync.c
index 9d48940..89bbc60 100644
--- a/labcodes/lab7/kern/sync/check_sync.c
+++ b/labcodes/lab7/kern/sync/check_sync.c
@@ -13,6 +13,66 @@
 #define TIMES  4 /* 吃4次饭 */
 #define SLEEP_TIME 10
 
+//-----------------philosopher problem using monitor ------------
+/*PSEUDO CODE :philosopher problem using semaphore
+system DINING_PHILOSOPHERS
+
+VAR
+me:    semaphore, initially 1;                    # for mutual exclusion 
+s[5]:  semaphore s[5], initially 0;               # for synchronization 
+pflag[5]: {THINK, HUNGRY, EAT}, initially THINK;  # philosopher flag 
+
+# As before, each philosopher is an endless cycle of thinking and eating.
+
+procedure philosopher(i)
+  {
+    while TRUE do
+     {
+       THINKING;
+       take_chopsticks(i);
+       EATING;
+       drop_chopsticks(i);
+     }
+  }
+
+# The take_chopsticks procedure involves checking the status of neighboring 
+# philosophers and then declaring one's own intention to eat. This is a two-phase 
+# protocol; first declaring the status HUNGRY, then going on to EAT.
+
+procedure take_chopsticks(i)
+  {
+    DOWN(me);               # critical section 
+    pflag[i] := HUNGRY;
+    test[i];
+    UP(me);                 # end critical section 
+    DOWN(s[i])              # Eat if enabled 
+   }
+
+void test(i)                # Let phil[i] eat, if waiting 
+  {
+    if ( pflag[i] == HUNGRY
+      && pflag[i-1] != EAT
+      && pflag[i+1] != EAT)
+       then
+        {
+          pflag[i] := EAT;
+          UP(s[i])
+         }
+    }
+
+
+# Once a philosopher finishes eating, all that remains is to relinquish the 
+# resources---its two chopsticks---and thereby release waiting neighbors.
+
+void drop_chopsticks(int i)
+  {
+    DOWN(me);                # critical section 
+    test(i-1);               # Let phil. on left eat if possible 
+    test(i+1);               # Let phil. on rght eat if possible 
+    UP(me);                  # up critical section 
+   }
+
+*/
 //---------- philosophers problem using semaphore ----------------------
 int state_sema[N]; /* 记录每个人状态的数组 */
 /* 信号量是一个特殊的整型变量 */
diff --git a/labcodes_answer/lab7_result/kern/sync/check_sync.c b/labcodes_answer/lab7_result/kern/sync/check_sync.c
index 95cf7da..05953c4 100644
--- a/labcodes_answer/lab7_result/kern/sync/check_sync.c
+++ b/labcodes_answer/lab7_result/kern/sync/check_sync.c
@@ -167,7 +167,7 @@ int philosopher_using_semaphore(void * arg) /* i：哲学家号码，从0到N-1
 
 struct proc_struct *philosopher_proc_condvar[N]; // N philosopher
 int state_condvar[N];                            // the philosopher's state: EATING, HUNGARY, THINKING  
-monitor_t mt, *mtp=&mt;                                    // mp is mutex semaphore for monitor's procedures
+monitor_t mt, *mtp=&mt;                          // monitor
 
 void phi_test_condvar (i) { 
     if(state_condvar[i]==HUNGRY&&state_condvar[LEFT]!=EATING