use a mutex to make requestJSONBufferLock / releaseJSONBufferLock robust

similar to upstream wled#4089,
but with slightly different "failure" logic.

Author: softhack007

wled00/util.cpp

@@ -222,17 +222,31 @@ bool isAsterisksOnly(const char* str, byte maxLen)
 //threading/network callback details: https://github.com/Aircoookie/WLED/pull/2336#discussion_r762276994
 bool requestJSONBufferLock(uint8_t module)
 {
-  unsigned long now = millis();
-
-  while (jsonBufferLock && millis()-now < 1100) delay(1); // wait for fraction for buffer lock
+  bool haveLock = false;
+  #ifdef ARDUINO_ARCH_ESP32
+    // We use a recursive mutex to prevent parallel JSON writes from parallel tasks.
+    // This also fixes hanging up for the full timeout interval in cases when the contention is from the same task.
+    // see https://github.com/wled/WLED/pull/4089 for more details.
+    if (esp32SemTake(jsonBufferLockMutex, 1800) == pdTRUE) haveLock = true;  // WLEDMM must wait longer than suspendStripService timeout = 1500ms
+  #else
+    // 8266: only wait in case that can_yield() tells us we can yield and delay
+    if (can_yield()) {
+      unsigned long now = millis();
+      while (jsonBufferLock && millis()-now < 1800) delay(1); // wait for fraction for buffer lock // WLEDMM must wait longer than suspendStripService timeout = 1500ms
+      if (!jsonBufferLock) haveLock = true;
+    }
+  #endif
 
-  if (jsonBufferLock) {
+  if (jsonBufferLock || !haveLock) {
+    if (haveLock) esp32SemGive(jsonBufferLockMutex);  // we got the mutex, but jsonBufferLock says the opposite -> give up
+    delay(10); // WLEDMM experimental: small extra wait, in case that esp32 cores temporarily disagree on the value of jsonBufferLock
     USER_PRINT(F("ERROR: Locking JSON buffer failed! (still locked by "));
     USER_PRINT(jsonBufferLock);
     USER_PRINTLN(")");
     return false; // waiting time-outed
   }
 
+  // success - we keep holding the mutex until releaseJSONBufferLock()
   jsonBufferLock = module ? module : 255;
   DEBUG_PRINT(F("JSON buffer locked. ("));
   DEBUG_PRINT(jsonBufferLock);
@@ -250,6 +264,7 @@ void releaseJSONBufferLock()
   DEBUG_PRINTLN(")");
   fileDoc = nullptr;
   jsonBufferLock = 0;
+  esp32SemGive(jsonBufferLockMutex); // return the mutex
 }