Explain the usage of is_valid in pthread mutexes
Document the usage inside the library, and relate it with how it's
additionally used in the test code.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/threading.c b/library/threading.c
index 2bb932d..2de117f 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -67,6 +67,12 @@
if( mutex == NULL )
return;
+ /* A nonzero value of is_valid indicates a successfully initialized
+ * mutex. This is a workaround for not being able to return an error
+ * code for this function. The lock/unlock functions return an error
+ * if is_valid is nonzero. The Mbed TLS unit test code uses this field
+ * to distinguish more states of the mutex; see
+ * tests/src/threading_helpers for details. */
mutex->is_valid = pthread_mutex_init( &mutex->mutex, NULL ) == 0;
}