ESP8266: makes guarding variable for deferring events atomic

Author: Veijo Pesonen

components/wifi/esp8266-driver/ESP8266Interface.cpp

@@ -26,6 +26,7 @@
 #include "features/netsocket/nsapi_types.h"
 #include "mbed_trace.h"
 #include "platform/Callback.h"
+#include "platform/mbed_critical.h"
 #include "platform/mbed_debug.h"
 #include "platform/mbed_wait_api.h"
 
@@ -496,7 +497,7 @@ int ESP8266Interface::socket_close(void *handle)
 
     _cbs[socket->id].callback = NULL;
     _cbs[socket->id].data = NULL;
-    _cbs[socket->id].deferred = false;
+    core_util_atomic_store_u8(&_cbs[socket->id].deferred, false);
 
     socket->connected = false;
     _sock_i[socket->id].open = false;
@@ -566,6 +567,7 @@ int ESP8266Interface::socket_send(void *handle, const void *data, unsigned size)
 {
     nsapi_error_t status;
     struct esp8266_socket *socket = (struct esp8266_socket *)handle;
+    uint8_t expect_false = false;
 
     if (!socket) {
         return NSAPI_ERROR_NO_SOCKET;
@@ -578,9 +580,10 @@ int ESP8266Interface::socket_send(void *handle, const void *data, unsigned size)
 
     status = _esp.send(socket->id, data, size);
 
-    if (status == NSAPI_ERROR_WOULD_BLOCK && !_cbs[socket->id].deferred && socket->proto == NSAPI_TCP) {
+    if (status == NSAPI_ERROR_WOULD_BLOCK
+        && socket->proto == NSAPI_TCP
+        && core_util_atomic_cas_u8(&_cbs[socket->id].deferred, &expect_false, true)) {
         tr_debug("Postponing SIGIO from the device");
-        _cbs[socket->id].deferred = true;
         _global_event_queue->call_in(50, callback(this, &ESP8266Interface::event_deferred));
     } else if (status == NSAPI_ERROR_WOULD_BLOCK && socket->proto == NSAPI_UDP) {
         status = NSAPI_ERROR_DEVICE_ERROR;
@@ -734,8 +737,8 @@ void ESP8266Interface::event()
 void ESP8266Interface::event_deferred()
 {
     for (int i = 0; i < ESP8266_SOCKET_COUNT; i++) {
-        if (_cbs[i].deferred && _cbs[i].callback) {
-            _cbs[i].deferred = false;
+        uint8_t expect_true = true;
+        if (core_util_atomic_cas_u8(&_cbs[i].deferred, &expect_true, false) && _cbs[i].callback) {
             _cbs[i].callback(_cbs[i].data);
         }
     }

components/wifi/esp8266-driver/ESP8266Interface.h

@@ -373,7 +373,7 @@ class ESP8266Interface : public NetworkStack, public WiFiInterface {
     struct {
         void (*callback)(void *);
         void *data;
-        bool deferred;
+        uint8_t deferred;
     } _cbs[ESP8266_SOCKET_COUNT];
     void event();
     void event_deferred();