core: introduce KERNEL_PID_FIRST and KERNEL_PID_LAST

core/include/kernel_types.h

@@ -5,19 +5,35 @@
 #include <inttypes.h>
 
 /**
- * @def KERNEL_PID_UNDEF
- * @brief Identifier to detect an invalid PID
+ * @def MAXTHREADS
+ * @brief The maximum number of threads to be scheduled
+ */
+#ifndef MAXTHREADS
+#define MAXTHREADS 32
+#endif
+
+/**
+ * Canonical identifier for an invalid PID.
  */
 #define KERNEL_PID_UNDEF -1
 
+/**
+ * The first valid PID (inclusive).
+ */
+#define KERNEL_PID_FIRST (KERNEL_PID_UNDEF + 1)
+
+/**
+ * The last valid PID (inclusive).
+ */
+#define KERNEL_PID_LAST (KERNEL_PID_FIRST + MAXTHREADS - 1)
+
 /**
  * Macro for printing formatter
  */
 #define PRIkernel_pid PRIi16
 
 /**
- * @brief Unique process identifier
- *
+ * Unique process identifier
  */
 typedef int16_t kernel_pid_t;
 

core/include/sched.h

@@ -84,8 +84,7 @@
 #include "bitarithm.h"
 #include "tcb.h"
 #include "attributes.h"
-
-#define MAXTHREADS 32 /**< the maximum number of threads to be scheduled */
+#include "kernel_types.h"
 
 /**
  * @def SCHED_PRIO_LEVELS

core/thread.c

@@ -39,7 +39,7 @@ inline kernel_pid_t thread_getpid(void)
 
 volatile tcb_t *thread_get(kernel_pid_t pid)
 {
-    if ((pid != KERNEL_PID_UNDEF) && (0 <= pid) && (pid < MAXTHREADS)) {
+    if ((pid != KERNEL_PID_UNDEF) && (KERNEL_PID_FIRST <= pid) && (pid <= KERNEL_PID_LAST)) {
         return sched_threads[pid];
     }
     return NULL;
@@ -158,19 +158,14 @@ kernel_pid_t thread_create(char *stack, int stacksize, char priority, int flags,
         dINT();
     }
 
-    kernel_pid_t pid = 0;
-
-    while (pid < MAXTHREADS) {
-        if (sched_threads[pid] == NULL) {
-            sched_threads[pid] = cb;
-            cb->pid = pid;
+    kernel_pid_t pid = KERNEL_PID_UNDEF;
+    for (kernel_pid_t i = KERNEL_PID_FIRST; i <= KERNEL_PID_LAST; ++i) {
+        if (sched_threads[i] == NULL) {
+            pid = i;
             break;
         }
-
-        pid++;
     }
-
-    if (pid == MAXTHREADS) {
+    if (pid == KERNEL_PID_UNDEF) {
         DEBUG("thread_create(): too many threads!\n");
 
         if (!inISR()) {
@@ -180,6 +175,9 @@ kernel_pid_t thread_create(char *stack, int stacksize, char priority, int flags,
         return -EOVERFLOW;
     }
 
+    sched_threads[pid] = cb;
+
+    cb->pid = pid;
     cb->sp = thread_stack_init(function, arg, stack, stacksize);
     cb->stack_start = stack;
 

sys/ps/ps.c

@@ -21,6 +21,7 @@
 #include "hwtimer.h"
 #include "sched.h"
 #include "tcb.h"
+#include "kernel_types.h"
 
 /* list of states copied from tcb.h */
 const char *state_names[] = {
@@ -40,7 +41,6 @@ const char *state_names[] = {
 void thread_print_all(void)
 {
     const char queued_name[] = {'_', 'Q'};
-    int i;
 #ifdef DEVELHELP
     int overall_stacksz = 0, overall_used = 0;
 #endif
@@ -56,7 +56,7 @@ void thread_print_all(void)
            "\n"
            , "name", "state");
 
-    for (i = 0; i < MAXTHREADS; i++) {
+    for (kernel_pid_t i = KERNEL_PID_FIRST; i <= KERNEL_PID_LAST; i++) {
         tcb_t *p = (tcb_t *)sched_threads[i];
 
         if (p != NULL) {