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copied!<p>Since you want to know <code>how to code your algorithm for 1 restroom</code>, I have done so in C. It will be a fairly simple task to convert it into C--, as all the semaphore constructs appear quite similar.</p> <p>From what I could make of your answer,</p> <pre><code>C: sem_wait() C--: wait() sem_post() signal() sem_t semaphore() sem_init() initialsem() </code></pre> <p>Bear in mind, as stated, I have worked out the problem for <strong>1-restroom</strong> only. Since this is homework, I expect you to expand it into the <strong>2-restrooms</strong> form yourself.</p> <p>Working one's way from the <a href="http://en.wikipedia.org/wiki/Readers-writers_problem" rel="nofollow">Readers-writers problem</a> to our "Unisex Restroom" problem, we make use of the following global variables:</p> <pre><code>int mcount,wcount; // count of number of men/women in restroom sem_t x,y,z; // semaphores for updating mcount & wcount values safely sem_t wsem,msem; // semaphores to block other genders' entry sem_t cap; // capacity of the restroom </code></pre> <p>Incorporating these semaphores & counters into the <code>man</code> thread function,</p> <pre><code>void *man(void *param) { sem_wait(&z); sem_wait(&msem); sem_wait(&x); mcount++; if(mcount==1) { sem_wait(&wsem); } // first man in, make women wait sem_post(&x); sem_post(&msem); sem_post(&z); sem_wait(&cap); //wait here, if over capacity printf("\t\tman in!\n"); delay(); printf("\t\t\tman out!\n"); sem_post(&cap); //one man has left, increase capacity sem_wait(&x); mcount--; if(mcount==0) {sem_post(&wsem);} // no man left, signal women sem_post(&x); } </code></pre> <p>Similarly, the woman thread function, substitutes <code>mcount</code> with <code>wcount</code>, <code>msem</code> with <code>wsem</code>, and <code>x</code> with <code>y</code>. Only <code>z</code> remains as is in the <code>man</code> function, so that both <code>man</code> & <code>woman</code> threads queue up on the same common semaphore. (Due to this, the code invariably has <strong>FIFO-like</strong> behaviour, which ensures <strong>fairness/non-starvation</strong>)</p> <p>The complete code is as follows: (To compile, use <code>gcc filename -lpthread</code>)</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <semaphore.h> int mcount,wcount; sem_t x,y,z,wsem,msem,cap; void delay(void) { int i; int delaytime; delaytime = random(); for (i = 0; i<delaytime; i++); } void *woman(void *param) { sem_wait(&z); sem_wait(&wsem); sem_wait(&y); wcount++; if(wcount==1) { sem_wait(&msem); } sem_post(&y); sem_post(&wsem); sem_post(&z); sem_wait(&cap); printf("woman in!\n"); delay(); printf("\twoman out!\n"); sem_post(&cap); sem_wait(&y); wcount--; if(wcount==0) { sem_post(&msem); } sem_post(&y); } void *man(void *param) { sem_wait(&z); sem_wait(&msem); sem_wait(&x); mcount++; if(mcount==1) { sem_wait(&wsem); } sem_post(&x); sem_post(&msem); sem_post(&z); sem_wait(&cap); printf("\t\tman in!\n"); delay(); printf("\t\t\tman out!\n"); sem_post(&cap); sem_wait(&x); mcount--; if(mcount==0) {sem_post(&wsem);} sem_post(&x); } int main(void) { int i; srandom(60); mcount = 0; wcount = 0; sem_init(&x,0,1); // for sem_init, initial value is 3rd argument sem_init(&y,0,1); sem_init(&z,0,1); sem_init(&wsem,0,1); sem_init(&msem,0,1); sem_init(&cap,0,4); // eg. cap initialized to 4 pthread_t *tid; tid = malloc(80*sizeof(pthread_t)); // You can use your cobegin statement here, instead of pthread_create() // I have forgone the use of pthread barriers although I suppose they would nicely imitate the functionality of cobegin. // This is merely to retain simplicity. for(i=0;i<10;i++) { pthread_create(&tid[i],NULL,woman,NULL); } for(i=10;i<20;i++) { pthread_create(&tid[i],NULL,man,NULL); } for(i=0;i<20;i++) { pthread_join(tid[i],NULL); } return(0); } </code></pre> <p>While converting into the <strong>2-restrooms</strong> form, make note of which semaphores & counter variables you would need to duplicate to satisfy all the conditions. Happy <em>semaphoring</em>!</p>

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