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@ -13,6 +13,66 @@ |
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#define TIMES 4 /* 吃4次饭 */ |
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#define SLEEP_TIME 10 |
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//-----------------philosopher problem using monitor ------------ |
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/*PSEUDO CODE :philosopher problem using semaphore |
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system DINING_PHILOSOPHERS |
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VAR |
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me: semaphore, initially 1; # for mutual exclusion |
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s[5]: semaphore s[5], initially 0; # for synchronization |
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pflag[5]: {THINK, HUNGRY, EAT}, initially THINK; # philosopher flag |
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# As before, each philosopher is an endless cycle of thinking and eating. |
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procedure philosopher(i) |
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{ |
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while TRUE do |
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{ |
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THINKING; |
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take_chopsticks(i); |
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EATING; |
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drop_chopsticks(i); |
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} |
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} |
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# The take_chopsticks procedure involves checking the status of neighboring |
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# philosophers and then declaring one's own intention to eat. This is a two-phase |
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# protocol; first declaring the status HUNGRY, then going on to EAT. |
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procedure take_chopsticks(i) |
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{ |
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DOWN(me); # critical section |
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pflag[i] := HUNGRY; |
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test[i]; |
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UP(me); # end critical section |
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DOWN(s[i]) # Eat if enabled |
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} |
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void test(i) # Let phil[i] eat, if waiting |
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{ |
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if ( pflag[i] == HUNGRY |
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&& pflag[i-1] != EAT |
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&& pflag[i+1] != EAT) |
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then |
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{ |
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pflag[i] := EAT; |
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UP(s[i]) |
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} |
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} |
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# Once a philosopher finishes eating, all that remains is to relinquish the |
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# resources---its two chopsticks---and thereby release waiting neighbors. |
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void drop_chopsticks(int i) |
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{ |
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DOWN(me); # critical section |
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test(i-1); # Let phil. on left eat if possible |
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test(i+1); # Let phil. on rght eat if possible |
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UP(me); # up critical section |
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} |
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*/ |
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//---------- philosophers problem using semaphore ---------------------- |
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int state_sema[N]; /* 记录每个人状态的数组 */ |
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/* 信号量是一个特殊的整型变量 */ |
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