Handout

kernel/sync/semaphore.cc

@@ -0,0 +1,22 @@
+#include "./semaphore.h"
+
+#include "../interrupt/guard.h"
+#include "../thread/thread.h"
+
+void Semaphore::p(Vault &vault) {
+	if (counter == 0) {
+		waiting.enqueue(*vault.scheduler.active());
+		vault.scheduler.resume(false);
+	} else {
+		counter--;
+	}
+}
+
+void Semaphore::v(Vault &vault) {
+	Thread *customer = waiting.dequeue();
+	if (customer != nullptr) {
+		vault.scheduler.ready(customer);
+	} else {
+		counter++;
+	}
+}