semaphore: add a new semaphore_timedwait helper

This is the same as semaphore_wait except it allows for the acquire
attempt to time out after a given period of time.

kernel-src/include/semaphore.h

@@ -4,6 +4,7 @@
 #include <stddef.h>
 #include <stdbool.h>
 #include <spinlock.h>
+#include <time.h>
 
 #define SEM_TAIL 0
 #define SEM_HEAD 1
@@ -24,6 +25,7 @@ typedef struct semaphore_t{
 
 
 int semaphore_wait(semaphore_t *sem, bool interruptible);
+int semaphore_timedwait(semaphore_t *sem, time_t timeoutusec, bool interruptible);
 void semaphore_signal(semaphore_t *sem);
 bool semaphore_test(semaphore_t *sem);
 bool semaphore_haswaiters(semaphore_t *sem);

kernel-src/lib/semaphore.c

@@ -88,6 +88,23 @@ int semaphore_wait(semaphore_t *sem, bool interruptible) {
 	return ret;
 }
 
+int semaphore_timedwait(semaphore_t *sem, time_t timeoutusec, bool interruptible) {
+	time_t sleepus;
+
+	do {
+		if (semaphore_test(sem))
+			return true;
+
+		sleepus = min(timeoutusec, 10);
+		timeoutusec -= sleepus;
+
+		if (sleepus)
+			sched_sleepus(sleepus);
+	} while (timeoutusec);
+
+	return false;
+}
+
 void semaphore_signal(semaphore_t *sem) {
 	bool intstate = interrupt_set(false);
 	spinlock_acquire(&sem->lock);