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int readcount=0, writecount=0;
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semaphore mutex1=1, mutex2=1, mutex3=1, w=1, r=1 ;
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读者进程：
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P(mutex 3);
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P(r);
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P(mutex 1);
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readcount++;
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if (readcount == 1 ) P(w);
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V(mutex 1);
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V(r);
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V(mutex 3);
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    reading is performed
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P(mutex 1);
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readcount --;
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if (readcount == 0 ) V(w);
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V(mutex 1);
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写者进程：
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P(mutex 2);
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writecount++;
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if (writecount == 1 )
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P(r);
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V(mutex 2);
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P(w);
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    writing is performed
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V(w);
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P(mutex 2);
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writecount --;
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if (writecount == 0) V(r);
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V(mutex 2);