Fix #323: Avoid infinite sem-speed-test

1. Add a hard limit to the execution (work) counter for the
sem-speed-test worker threads.  With this they will self-exit
eventually even if the root task never gets CPU time to stop them.

2. Set the priority of the worker tasks to be logically lower, so
it is less likely to preempt the main task.

Note that the logical priority is inverted from the numeric value.

src/tests/sem-speed-test/sem-speed-test.c

@@ -36,6 +36,25 @@
 #include "uttest.h"
 #include "utbsp.h"
 
+/*
+ * Note the worker priority must be lower than that of
+ * the executive (init) task.  Otherwise, the SemRun()
+ * function may may never get CPU time to stop the test.
+ */
+#define SEMTEST_TASK_PRIORITY   150
+
+/*
+ * A limit for the maximum amount
+ * of iterations that this test will
+ * perform.  This prevents the test
+ * from running infinitely in case the
+ * time-based stop routine does not
+ * work correctly.  See note above
+ * about priority requirements.
+ */
+#define SEMTEST_WORK_LIMIT      10000000
+
+
 /* Define setup and test functions for UT assert */
 void SemSetup(void);
 void SemRun(void);
@@ -54,8 +73,6 @@ void SemRun(void);
  */
 #define SEMOP(op)           SEMCALL(Count,op)
 
-#define TASK_PRIORITY  50
-
 uint32 task_1_id; 
 uint32 task_1_work;
 
@@ -72,7 +89,7 @@ void task_1(void)
     OS_printf("Starting task 1\n");
     OS_TaskRegister();
 
-    while(1)
+    while(task_1_work < SEMTEST_WORK_LIMIT)
     {
        status = SEMOP(Take)(sem_id_1);
        if ( status != OS_SUCCESS )
@@ -99,7 +116,7 @@ void task_2(void)
     OS_printf("Starting task 2\n");
     OS_TaskRegister();
 
-    while(1)
+    while(task_2_work < SEMTEST_WORK_LIMIT)
     {
        status = SEMOP(Take)(sem_id_2);
        if ( status != OS_SUCCESS )
@@ -150,10 +167,10 @@ void SemSetup(void)
    /*
    ** Create the tasks
    */
-   status = OS_TaskCreate( &task_1_id, "Task 1", task_1, NULL, 4096, TASK_PRIORITY, 0);
+   status = OS_TaskCreate( &task_1_id, "Task 1", task_1, NULL, 4096, SEMTEST_TASK_PRIORITY, 0);
    UtAssert_True(status == OS_SUCCESS, "Task 1 create Id=%u Rc=%d", (unsigned int)task_1_id, (int)status);
 
-   status = OS_TaskCreate( &task_2_id, "Task 2", task_2, NULL, 4096, TASK_PRIORITY, 0);
+   status = OS_TaskCreate( &task_2_id, "Task 2", task_2, NULL, 4096, SEMTEST_TASK_PRIORITY, 0);
    UtAssert_True(status == OS_SUCCESS, "Task 2 create Id=%u Rc=%d", (unsigned int)task_2_id, (int)status);
 
    /* A small delay just to allow the tasks
@@ -173,6 +190,9 @@ void SemRun(void)
 
     /*
     ** Delete resources
+    **
+    ** NOTE: if the work limit was reached, the
+    ** OS_TaskDelete calls may return non-success.
     */
     status = OS_TaskDelete( task_1_id );
     UtAssert_True(status == OS_SUCCESS, "Task 1 delete Rc=%d", (int)status);