sys/xtimer: implement mutex lock with timeout

sys/include/xtimer.h

@@ -32,6 +32,7 @@
 #include <stdint.h>
 #include "timex.h"
 #include "msg.h"
+#include "mutex.h"
 
 #include "board.h"
 #include "periph_conf.h"
@@ -425,6 +426,19 @@ static inline bool xtimer_less(xtimer_ticks32_t a, xtimer_ticks32_t b);
  */
 static inline bool xtimer_less64(xtimer_ticks64_t a, xtimer_ticks64_t b);
 
+/**
+ * @brief lock a mutex but with timeout
+ *
+ * @note this requires core_thread_flags to be enabled
+ *
+ * @param[in]    mutex  mutex to lock
+ * @param[in]    us     timeout in microseconds relative
+ *
+ * @return       0, when returned after mutex was locked
+ * @return       -1, when the timeout occcured
+ */
+int xtimer_mutex_lock_timeout(mutex_t *mutex, uint64_t us);
+
 /**
  * @brief xtimer backoff value
  *

sys/xtimer/xtimer.c

@@ -26,12 +26,19 @@
 #include "thread.h"
 #include "irq.h"
 #include "div.h"
+#include "list.h"
 
 #include "timex.h"
 
 #define ENABLE_DEBUG 0
 #include "debug.h"
 
+typedef struct {
+    mutex_t *mutex;
+    thread_t *thread;
+    int timeout;
+} mutex_thread_t;
+
 static void _callback_unlock_mutex(void* arg)
 {
     mutex_t *mutex = (mutex_t *) arg;
@@ -220,3 +227,29 @@ int _xtimer_msg_receive_timeout(msg_t *msg, uint32_t timeout_ticks)
     _xtimer_set_msg(&t, timeout_ticks, &tmsg, sched_active_pid);
     return _msg_wait(msg, &tmsg, &t);
 }
+
+static void _mutex_timeout(void *arg)
+{
+    mutex_thread_t *mt = (mutex_thread_t *)arg;
+
+    mt->timeout = 1;
+    sched_set_status(mt->thread, STATUS_PENDING);
+    list_remove(&mt->mutex->queue, (list_node_t *)&mt->thread->rq_entry);
+    thread_yield_higher();
+}
+
+int xtimer_mutex_lock_timeout(mutex_t *mutex, uint64_t timeout)
+{
+    xtimer_t t;
+    mutex_thread_t mt = { mutex, (thread_t *)sched_active_thread, 0 };
+
+    if (timeout != 0) {
+        t.callback = _mutex_timeout;
+        t.arg = (void *)((mutex_thread_t *)&mt);
+        _xtimer_set64(&t, timeout, timeout >> 32);
+    }
+
+    mutex_lock(mutex);
+    xtimer_remove(&t);
+    return -mt.timeout;
+}