requestJSONBufferLock: Fix locking implementation

On ESP8266, it isn't permissible to call delay() in system context;
ensure this is legal before waiting.

On ESP32, use an operating system mutex to ensure consistent variable
state in a multicore environment, and manage the wait without needing
to loop.

wled00/util.cpp

@@ -213,15 +213,31 @@ bool requestJSONBufferLock(uint8_t module)
     DEBUG_PRINTLN(F("ERROR: JSON buffer not allocated!"));
     return false;
   }
+
+#if defined(ARDUINO_ARCH_ESP32)
+  // Use a recursive mutex type in case our task is the one holding the JSON buffer.
+  // This can happen during large JSON web transactions.  In this case, we continue immediately
+  // and then will return out below if the lock is still held.
+  if (xSemaphoreTakeRecursive(jsonBufferLockMutex, 250) == pdFALSE) return false;  // timed out waiting
+#elif defined(ARDUINO_ARCH_ESP8266)
+  // If we're in system context, delay() won't return control to the user context, so there's
+  // no point in waiting.
+  if (can_yield()) {
     unsigned long now = millis();
-
+    while (jsonBufferLock && (millis()-now < 250)) delay(1); // wait for fraction for buffer lock
-  while (jsonBufferLock && millis()-now < 250) delay(1); // wait for fraction for buffer lock
+  }
-
+#else
+  #error Unsupported task framework - fix requestJSONBufferLock
+#endif  
+  // If the lock is still held - by us, or by another task
   if (jsonBufferLock) {
     DEBUG_PRINT(F("ERROR: Locking JSON buffer failed! (still locked by "));
     DEBUG_PRINT(jsonBufferLock);
     DEBUG_PRINTLN(")");
-    return false; // waiting time-outed
+#ifdef ARDUINO_ARCH_ESP32
+    xSemaphoreGiveRecursive(jsonBufferLockMutex);
+#endif
+    return false;
   }
 
   jsonBufferLock = module ? module : 255;
@@ -239,6 +255,9 @@ void releaseJSONBufferLock()
   DEBUG_PRINT(jsonBufferLock);
   DEBUG_PRINTLN(")");
   jsonBufferLock = 0;
+#ifdef ARDUINO_ARCH_ESP32
+  xSemaphoreGiveRecursive(jsonBufferLockMutex);
+#endif  
 }
 
 

wled00/wled.h

@@ -810,6 +810,7 @@ WLED_GLOBAL int8_t spi_sclk  _INIT(SPISCLKPIN);
 // global ArduinoJson buffer
 #if defined(ARDUINO_ARCH_ESP32)
 WLED_GLOBAL JsonDocument *pDoc _INIT(nullptr);
+WLED_GLOBAL SemaphoreHandle_t jsonBufferLockMutex _INIT(xSemaphoreCreateRecursiveMutex());
 #else
 WLED_GLOBAL StaticJsonDocument<JSON_BUFFER_SIZE> gDoc;
 WLED_GLOBAL JsonDocument *pDoc _INIT(&gDoc);