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Postsdbo
PO
 

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  1. PO
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    <p>What you need is 2 threads (parent and child) allowing each other to execute. </p> <p>This is the pseudo-code, you are free to use any locking primitives you want.</p> <pre><code>//global variables and initializations parent_lock = UNLOCKED; //This allows your first print to be from parent child_lock = LOCKED; parent_counter = 0; //to count the number of prints child_counter = 0; //Parent should do this | //Child should do this while(1) |while(1) { | spin: if(parent_lock == LOCKED) |spin: if(child_lock == LOCKED) { | { //spin till child unlocks you | //spin till parent unlocks you goto spin; | goto spin; } | } else | else { | { print("PARENT"); | print("CHILD"); parent_counter++; | child_counter++; //lock yourself allow the other| //lock yourself allow the other parent_lock = LOCKED; | child_lock = LOCKED; child_lock = UNLOCKED; | parent_lock = UNLOCKED; if (parent_counter == 10) | if (child_counter == 10) { | { break;//printed 10 times | break; } | } } | } } |} //PARENT has printed 10times wait for |//CHILD has printed 10times wait for //child |// parent </code></pre> <p><strong>PS</strong>: *I assume you are free to spin on a lock which is what I have done, if that's not the case you need to modify the above algorithm to do sleep and wake up instead of spin.<br> *You can choose pthread lock primitives to initialize the parent_lock and child_lock.<br> *For the program to be correct we need to assume that assignment statements are atomic Ex: child_lock = LOCKED statement is atomic.</p> <p><strong>Extremely Important</strong>: See the order in parent:</p> <pre><code>parent_lock = LOCKED; child_lock = UNLOCKED; </code></pre> <p>and its counter part in the child thread. If you interchange this two lines then you may DEADLOCK!!!!, because of a sequence of mixed execution by parent and child(due to OS scheduler).</p>
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    1. POProducer consumer only mutexes
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    1. USDeepthought
    1. USDeepthought
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    1. COThis was my first idea, but with pthread mutexes you wouldn't be (reliably) able to unlock the parent lock from the child and vice versa: " If the calling thread does not currently hold the mutex (via a previous call to pthread_mutex_lock() or pthread_mutex_trylock()) the unlock request will fail with the EPERM result."
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      1. USTaylor Brandstetter
 

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