42 lines
1.3 KiB
C++
42 lines
1.3 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/queue
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lock.acquire();
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if (counter > 0) {
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// Semaphore can be acquired
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counter = counter - 1;
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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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if (!wait_queue.initialized()) { // TODO: I will replace this suboptimal datastructure in the future
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wait_queue.reserve();
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}
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wait_queue.push_back(scheduler.get_active());
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CPU::disable_int(); // Make sure the block() comes through after releasing the lock
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lock.release();
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scheduler.block(); // Moves to next thread, enables int
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}
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}
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void Semaphore::v() {
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lock.acquire();
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if (!wait_queue.empty()) {
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// Semaphore stays busy and unblocks next thread to work in critical section
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unsigned int tid = wait_queue.front();
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wait_queue.erase(wait_queue.begin());
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CPU::disable_int(); // Make sure the deblock() comes through after releasing the lock
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lock.release();
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scheduler.deblock(tid); // Enables int
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} else {
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// No more threads want to work so free semaphore
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counter = counter + 1;
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lock.release();
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}
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}
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