3 files changed, 52 insertions, 3 deletions
diff --git a/kern/semaphore.c b/kern/semaphore.c
index 7e94dafd..72e843a9 100644
--- a/kern/semaphore.c
+++ b/kern/semaphore.c
@@ -15,19 +15,25 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <assert.h>
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdint.h>
 
 #include <kern/semaphore.h>
 #include <kern/semaphore_i.h>
 #include <kern/sleepq.h>
 
-void
-semaphore_wait_slow(struct semaphore *semaphore)
+static int
+semaphore_wait_slow_common(struct semaphore *semaphore,
+                           bool timed, uint64_t ticks)
 {
     struct sleepq *sleepq;
     unsigned long flags;
     unsigned int prev;
+    int error;
+
+    error = 0;
 
     sleepq = sleepq_lend(semaphore, false, &flags);
 
@@ -38,10 +44,35 @@ semaphore_wait_slow(struct semaphore *semaphore)
             break;
         }
 
-        sleepq_wait(sleepq, "sem");
+        if (!timed) {
+            sleepq_wait(sleepq, "sem");
+        } else {
+            error = sleepq_timedwait(sleepq, "sem", ticks);
+
+            if (error) {
+                break;
+            }
+        }
     }
 
     sleepq_return(sleepq, flags);
+
+    return error;
+}
+
+void
+semaphore_wait_slow(struct semaphore *semaphore)
+{
+    int error;
+
+    error = semaphore_wait_slow_common(semaphore, false, 0);
+    assert(!error);
+}
+
+int
+semaphore_timedwait_slow(struct semaphore *semaphore, uint64_t ticks)
+{
+    return semaphore_wait_slow_common(semaphore, true, ticks);
 }
 
 void
diff --git a/kern/semaphore.h b/kern/semaphore.h
index e08927ec..e1acbf21 100644
--- a/kern/semaphore.h
+++ b/kern/semaphore.h
@@ -33,6 +33,7 @@
 #define _KERN_SEMAPHORE_H
 
 #include <assert.h>
+#include <stdint.h>
 
 #include <kern/atomic.h>
 #include <kern/error.h>
@@ -93,6 +94,20 @@ semaphore_wait(struct semaphore *semaphore)
     }
 }
 
+static inline int
+semaphore_timedwait(struct semaphore *semaphore, uint64_t ticks)
+{
+    unsigned int prev;
+
+    prev = semaphore_dec(semaphore);
+
+    if (unlikely(prev == 0)) {
+        return semaphore_timedwait_slow(semaphore, ticks);
+    }
+
+    return 0;
+}
+
 /*
  * Unlock a semaphore.
  *
diff --git a/kern/semaphore_i.h b/kern/semaphore_i.h
index acd7cd48..6e79b137 100644
--- a/kern/semaphore_i.h
+++ b/kern/semaphore_i.h
@@ -19,6 +19,7 @@
 #define _KERN_SEMAPHORE_I_H
 
 #include <assert.h>
+#include <stdint.h>
 
 #include <kern/atomic.h>
 
@@ -56,6 +57,8 @@ semaphore_inc(struct semaphore *semaphore)
 
 void semaphore_wait_slow(struct semaphore *semaphore);
 
+int semaphore_timedwait_slow(struct semaphore *semaphore, uint64_t ticks);
+
 void semaphore_post_slow(struct semaphore *semaphore);
 
 #endif /* _KERN_SEMAPHORE_I_H */