voron

commit 2495223bb4a77539f2060d7b18038bdd3664e090
parent 72c0ea32616df5f6e4054a6e2cefb1801679a365
Author: oblique <psyberbits@gmail.com>
Date:   Mon,  5 Nov 2012 18:07:44 +0200

improved and safer semaphores

Diffstat:
M
include/semaphore.h
 | 
60
++++++++++++++++++++++++++----------------------------------

1 file changed, 26 insertions(+), 34 deletions(-)
diff --git a/include/semaphore.h b/include/semaphore.h
@@ -2,22 +2,25 @@
 #define __SEMAPHORE_H
 
 #include <io.h>
+#include <spinlock.h>
 #include <sched.h>
 
 typedef struct {
 	u32 counter;
+	spinlock_t lock;
 } semaphore_t;
 
 typedef struct {
 	semaphore_t sem;
 } mutex_t;
 
-#define SEMAPHORE_INIT(v)	{ (v) }
+#define SEMAPHORE_INIT(v)	{ (v), SPINLOCK_INIT }
 
 static inline void
 semaphore_init(semaphore_t *sem, u32 value)
 {
 	sem->counter = value;
+	INIT_SPINLOCK(&sem->lock);
 }
 
 /* returns 1 if managed to decreased the counter
@@ -25,53 +28,42 @@ semaphore_init(semaphore_t *sem, u32 value)
 static inline int
 semaphore_trywait(semaphore_t *sem)
 {
-	u32 tmp;
-
-	asm volatile (
-		"ldrex v1, [%1]		\n\t"
-		"teq v1, #0		\n\t"
-		"moveq %0, #1		\n\t"
-		"subne v1, v1, #1	\n\t"
-		"strexne %0, v1, [%1]	\n\t"
-		: "=&r" (tmp)
-		: "r" (&sem->counter)
-		: "v1", "memory", "cc"
-	);
-
-	if (tmp == 0) {
-		dmb();
-		return 1;
-	} else
+	spinlock_lock(&sem->lock);
+	if (sem->counter == 0) {
+		spinlock_unlock(&sem->lock);
 		return 0;
+	}
+	sem->counter--;
+	spinlock_unlock(&sem->lock);
+	return 1;
 }
 
 /* blocks until it manage to decrease the counter */
 static inline void
 semaphore_wait(semaphore_t *sem)
 {
-	while (!semaphore_trywait(sem))
-		suspend_task((u32)sem); /* sleep */
+	while (1) {
+		spinlock_lock(&sem->lock);
+		if (sem->counter == 0) {
+			suspend_task_no_schedule((u32)sem);
+			spinlock_unlock(&sem->lock);
+			schedule();
+			continue;
+		}
+		sem->counter--;
+		spinlock_unlock(&sem->lock);
+		break;
+	}
 }
 
 /* increases the counter and resumes other tasks */
 static inline void
 semaphore_done(semaphore_t *sem)
 {
-	dmb();
-	asm volatile (
-		"1:			\n\t"
-		"ldrex v1, [%0]		\n\t"
-		"add v1, v1, #1		\n\t"
-		"strex v2, v1, [%0]	\n\t"
-		"teq v2, #0		\n\t"
-		"bne 1b			\n\t"
-		:
-		: "r" (&sem->counter)
-		: "v1", "v2", "memory", "cc"
-	);
-	dmb();
-	/* resume tasks that use the same semaphore */
+	spinlock_lock(&sem->lock);
+	sem->counter++;
 	resume_tasks((u32)sem);
+	spinlock_unlock(&sem->lock);
 }