Merge pull request #17734 from gschorcht/sys/posix/pthread_newlib_com…

…patibility

sys/posix/pthread: newlib compatibility

sys/posix/pthread/include/pthread_once.h

@@ -23,15 +23,21 @@ extern "C" {
 
 /**
  * @brief Datatype to supply to pthread_once().
+ * @details This data type must be compatible with the one defined
+ * in newlib's `include/sys/_pthreadtypes.h`.
  */
-typedef volatile int pthread_once_t;
+typedef struct {
+ int is_initialized; /**< initialized */
+ int init_executed; /**< init function executed */
+} pthread_once_t;
 
 /**
  * @def PTHREAD_ONCE_INIT
  * @brief Initialization for pthread_once_t.
- * @details A zeroed out pthread_once_t is initialized.
+ * @details pthread_once_t variables are declared as initialized, but
+ * the init function is not yet executed.
  */
-#define PTHREAD_ONCE_INIT 0
+#define PTHREAD_ONCE_INIT  { 1, 0 }
 
 /**
  * @brief Helper function that ensures that `init_routine` is called at once.

sys/posix/pthread/pthread_once.c

@@ -22,11 +22,11 @@
 
 int pthread_once(pthread_once_t *once_control, void (*init_routine)(void))
 {
- if (*once_control == PTHREAD_ONCE_INIT) {
+ if (!once_control->init_executed) {
  init_routine();
  }
 
- *once_control = PTHREAD_ONCE_INIT + 1;
+ once_control->init_executed = 1;
 
  return 0;
 }