39 lines
1.1 KiB
C++
39 lines
1.1 KiB
C++
#include "Semaphore.h"
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#include "kernel/Globals.h"
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void Semaphore::p() {
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// Lock to allow deterministic operations on counter
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this->lock.acquire();
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if (this->counter > 0) {
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// Semaphore can be acquired
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this->counter = this->counter - 1;
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this->lock.release();
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} else {
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// Block and manage thread in semaphore queue until it's woken up by v() again
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this->wait_queue.push_back(scheduler.get_active());
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this->lock.release();
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scheduler.block(); // Moves to next thread
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}
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}
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void Semaphore::v() {
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this->lock.acquire();
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if (!this->wait_queue.empty()) {
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// Semaphore stays busy and unblocks next thread to work in critical section
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if (this->wait_queue.empty()) {
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this->lock.release();
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return;
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}
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unsigned int tid = this->wait_queue.front();
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this->wait_queue.erase(wait_queue.begin());
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this->lock.release();
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scheduler.deblock(tid);
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} else {
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// No more threads want to work so free semaphore
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this->counter = this->counter + 1;
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this->lock.release();
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}
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}
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