core: add support to see if there are messages available for the current thread

core/include/msg.h

@@ -224,6 +224,14 @@ int msg_reply(msg_t *m, msg_t *reply);
  */
 int msg_reply_int(msg_t *m, msg_t *reply);
 
+/**
+ * @brief Check how many messages are available in the message queue
+ *
+ * @return Number of messages available in our queue on success
+ * @return -1, if no caller's message queue is initialized
+ */
+int msg_avail(void);
+
 /**
  * @brief Initialize the current thread's message queue.
  *

core/msg.c

@@ -370,6 +370,22 @@ static int _msg_receive(msg_t *m, int block)
     DEBUG("This should have never been reached!\n");
 }
 
+int msg_avail(void)
+{
+    DEBUG("msg_available: %" PRIkernel_pid ": msg_available.\n",
+          sched_active_thread->pid);
+
+    tcb_t *me = (tcb_t*) sched_active_thread;
+
+    int queue_index = -1;
+
+    if (me->msg_array) {
+        queue_index = cib_avail(&(me->msg_queue));
+    }
+
+    return queue_index;
+}
+
 int msg_init_queue(msg_t *array, int num)
 {
     /* check if num is a power of two by comparing to its complement */

tests/thread_msg_avail/Makefile

@@ -0,0 +1,6 @@
+APPLICATION = thread_msg_avail
+include ../Makefile.tests_common
+
+DISABLE_MODULE += auto_init
+
+include $(RIOTBASE)/Makefile.include

tests/thread_msg_avail/main.c

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2015 Nick van IJzendoorn <nijzendoorn@engineering-spirit.nl>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief Thread test application
+ *
+ * @author Nick van IJzendoorn <nijzendoorn@engineering-spirit.nl>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <inttypes.h>
+
+#include "thread.h"
+#include "msg.h"
+
+#define MSG_QUEUE_LENGTH                (8)
+
+msg_t msg_queue[MSG_QUEUE_LENGTH];
+
+int main(void)
+{
+    msg_t msges[MSG_QUEUE_LENGTH];
+
+    msg_init_queue(msg_queue, MSG_QUEUE_LENGTH);
+
+    for (int idx = 0; idx < MSG_QUEUE_LENGTH; ++idx) {
+        msges[idx].sender_pid = thread_getpid();
+        msges[idx].type = idx;
+
+        msg_send_to_self(msges + idx);
+
+        printf("Add message %d\n", idx);
+
+        while (msg_avail() != (idx) + 1)
+            ; /* spin forever if we don't have the result we expect */
+    }
+
+    for (int idx = msg_avail(); idx > 0; --idx) {
+        msg_t msg;
+        msg_receive(&msg);
+
+        printf("Receive message: %d\n", (MSG_QUEUE_LENGTH - idx));
+
+        while (msg.type != (MSG_QUEUE_LENGTH - idx) || msg_avail() != idx - 1)
+            ; /* spin forever if we don't have the result we expect */
+    }
+
+    puts("TEST PASSED\n");
+    return 0;
+}