coap_cleanup: Support multiple usage

man/coap_init.txt.in

@@ -55,8 +55,12 @@ until *coap_cleanup*() is called.
 
 The *coap_cleanup*() function is used to cleanup / free any information set
 up by the *coap_startup*() function and should be the last *coap_**() function
-called. It is possible to call *coap_startup*() after *coap_cleanup*() to
-re-initialize the libcoap logic.
+called. The only safe function that can be called after *coap_cleanup*() is
+*coap_startup*() to re-initialize the libcoap logic.
+
+*NOTE:* Calling *coap_cleanup*() in one thread while continuing to use other
+*coap_**() function calls in a different thread is not supported - even if they
+are using a different coap_context_t.
 
 *NOTE:* All other libcoap cleanups should called prior to *coap_cleanup*(), e.g.
 *coap_free_context*(3).

src/coap_net.c

@@ -4453,6 +4453,9 @@ coap_startup(void) {
 
 void
 coap_cleanup(void) {
+  if (!coap_started)
+    return;
+  coap_started = 0;
 #if defined(HAVE_WINSOCK2_H)
   WSACleanup();
 #elif defined(WITH_CONTIKI)
@@ -4469,7 +4472,6 @@ coap_cleanup(void) {
   coap_mutex_destroy(&m_persist_add);
 #endif /* COAP_CONSTRAINED_STACK */
   coap_debug_reset();
-  coap_started = 0;
 }
 
 void

src/coap_threadsafe.c

@@ -33,8 +33,8 @@ coap_lock_unlock_func(coap_lock_t *lock, const char *file, int line) {
 
 int
 coap_lock_lock_func(coap_lock_t *lock, int force, const char *file, int line) {
-  if (!force && lock->being_freed) {
-    /* context is going away */
+  if ((!force && lock->being_freed) || !coap_started) {
+    /* context is going away or libcoap not initialized with coap_startup() */
     return 0;
   }
   if (coap_mutex_trylock(&lock->mutex)) {
@@ -88,8 +88,8 @@ coap_lock_unlock_func(coap_lock_t *lock) {
 
 int
 coap_lock_lock_func(coap_lock_t *lock, int force) {
-  if (!force && lock->being_freed) {
-    /* context is going away */
+  if ((!force && lock->being_freed) || !coap_started) {
+    /* context is going away or libcoap not initialized with coap_startup() */
     return 0;
   }
   /*