54 lines
1.1 KiB
C
54 lines
1.1 KiB
C
// Concurrent version of prime sieve of Eratosthenes.
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// Invented by Doug McIlroy, inventor of Unix pipes.
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// See http://swtch.com/~rsc/thread/.
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// The picture halfway down the page and the text surrounding it
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// explain what's going on here.
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//
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// Since NENV is 1024, we can print 1022 primes before running out.
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// The remaining two environments are the integer generator at the bottom
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// of main and user/idle.
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#include <inc/lib.h>
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unsigned
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primeproc(void)
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{
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int i, id, p;
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envid_t envid;
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// fetch a prime from our left neighbor
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top:
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p = ipc_recv(&envid, 0, 0);
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cprintf("CPU %d: %d ", thisenv->env_cpunum, p);
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// fork a right neighbor to continue the chain
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if ((id = fork()) < 0)
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panic("fork: %e", id);
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if (id == 0)
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goto top;
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// filter out multiples of our prime
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while (1) {
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i = ipc_recv(&envid, 0, 0);
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if (i % p)
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ipc_send(id, i, 0, 0);
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}
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}
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void
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umain(int argc, char **argv)
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{
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int i, id;
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// fork the first prime process in the chain
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if ((id = fork()) < 0)
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panic("fork: %e", id);
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if (id == 0)
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primeproc();
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// feed all the integers through
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for (i = 2; ; i++)
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ipc_send(id, i, 0, 0);
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}
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