Guard against multiple calls to IotMqtt_Init/IotMqtt_Cleanup (aws#613)

Author: gkwicker

libraries/standard/mqtt/src/iot_mqtt_api.c

@@ -41,6 +41,9 @@
 #include "platform/iot_clock.h"
 #include "platform/iot_threads.h"
 
+/* Atomics include. */
+#include "iot_atomic.h"
+
 /* Validate MQTT configuration settings. */
 #if IOT_MQTT_ENABLE_ASSERTS != 0 && IOT_MQTT_ENABLE_ASSERTS != 1
     #error "IOT_MQTT_ENABLE_ASSERTS must be 0 or 1."
@@ -60,6 +63,18 @@
 
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Uninitialized value for @ref _initCalled.
+ */
+#define MQTT_LIBRARY_UNINITIALIZED    ( ( uint32_t ) 0 )
+
+/**
+ * @brief Initialized value for @ref _initCalled.
+ */
+#define MQTT_LIBRARY_INITIALIZED      ( ( uint32_t ) 1 )
+
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Check if the library is initialized.
  *
@@ -243,15 +258,15 @@ static IotMqttError_t _subscriptionCommon( IotMqttOperationType_t operation,
  *
  * API functions will fail if @ref mqtt_function_init was not called.
  */
-static uint32_t _initCalled = 0;
+static volatile uint32_t _initCalled = MQTT_LIBRARY_UNINITIALIZED;
 
 /*-----------------------------------------------------------*/
 
 static bool _checkInit( void )
 {
     bool status = true;
 
-    if( _initCalled == 0 )
+    if( _initCalled == MQTT_LIBRARY_UNINITIALIZED )
     {
         IotLogError( "IotMqtt_Init was not called." );
 
@@ -994,35 +1009,37 @@ void _IotMqtt_DecrementConnectionReferences( _mqttConnection_t * pMqttConnection
 IotMqttError_t IotMqtt_Init( void )
 {
     IotMqttError_t status = IOT_MQTT_SUCCESS;
+    uint32_t allowInitialization = Atomic_CompareAndSwap_u32( &_initCalled,
+                                                              MQTT_LIBRARY_INITIALIZED,
+                                                              MQTT_LIBRARY_UNINITIALIZED );
 
-    if( _initCalled == 0 )
+    if( allowInitialization == 1 )
     {
         /* Call any additional serializer initialization function if serializer
          * overrides are enabled. */
         #if IOT_MQTT_ENABLE_SERIALIZER_OVERRIDES == 1
             #ifdef _IotMqtt_InitSerializeAdditional
                 if( _IotMqtt_InitSerializeAdditional() == false )
                 {
+                    /* Log initialization status. */
+                    IotLogError( "Failed to initialize MQTT library serializer. " );
+
                     status = IOT_MQTT_INIT_FAILED;
                 }
                 else
                 {
                     EMPTY_ELSE_MARKER;
                 }
-            #endif
+            #endif /* ifdef _IotMqtt_InitSerializeAdditional */
         #endif /* if IOT_MQTT_ENABLE_SERIALIZER_OVERRIDES == 1 */
 
-        /* Log initialization status. */
-        if( status != IOT_MQTT_SUCCESS )
+        if( status == IOT_MQTT_SUCCESS )
         {
-            IotLogError( "Failed to initialize MQTT library serializer. " );
+            IotLogInfo( "MQTT library successfully initialized." );
         }
         else
         {
-            /* Set the flag that specifies initialization is complete. */
-            _initCalled = 1;
-
-            IotLogInfo( "MQTT library successfully initialized." );
+            EMPTY_ELSE_MARKER;
         }
     }
     else
@@ -1037,10 +1054,12 @@ IotMqttError_t IotMqtt_Init( void )
 
 void IotMqtt_Cleanup( void )
 {
-    if( _initCalled == 1 )
-    {
-        _initCalled = 0;
+    uint32_t allowCleanup = Atomic_CompareAndSwap_u32( &_initCalled,
+                                                       MQTT_LIBRARY_UNINITIALIZED,
+                                                       MQTT_LIBRARY_INITIALIZED );
 
+    if( allowCleanup == 1 )
+    {
         /* Call any additional serializer cleanup initialization function if serializer
          * overrides are enabled. */
         #if IOT_MQTT_ENABLE_SERIALIZER_OVERRIDES == 1