Minimize GIL hold time: move lock after allocation

Move RedisModule_ThreadSafeContextLock to after MR_ALLOC to prevent
blocking Redis operations during memory allocation. The GIL is now only
held during the actual memcpy operation, not during allocation.

This should help prevent hangs in cluster environments with high
concurrency where holding the GIL during allocation could block other
Redis operations.

Author: gabsow

src/mr.c

@@ -584,15 +584,19 @@ static void MR_StepDone(Execution* e, void* pd) {
 static void MR_SetRecord(Execution* e, void* pd) {
     RedisModuleString* payload = pd;
 
-    RedisModule_ThreadSafeContextLock(mr_staticCtx);
     size_t dataLen;
-    const char* data = RedisModule_StringPtrLen(payload, &dataLen);
+    RedisModule_StringPtrLen(payload, &dataLen);
+
     char* buff_data = MR_ALLOC(dataLen);
     if (!buff_data) {
+        RedisModule_ThreadSafeContextLock(mr_staticCtx);
         RedisModule_FreeString(NULL, payload);
         RedisModule_ThreadSafeContextUnlock(mr_staticCtx);
         return;
     }
+
+    RedisModule_ThreadSafeContextLock(mr_staticCtx);
+    const char* data = RedisModule_StringPtrLen(payload, &dataLen);
     memcpy(buff_data, data, dataLen);
     RedisModule_FreeString(NULL, payload);
     RedisModule_ThreadSafeContextUnlock(mr_staticCtx);
@@ -622,14 +626,16 @@ static void MR_SetRecord(Execution* e, void* pd) {
 
 /* Remote function call, runs on the event loop */
 static void MR_PassRecord(RedisModuleCtx *ctx, const char *sender_id, uint8_t type, RedisModuleString* payload) {
-    RedisModule_ThreadSafeContextLock(mr_staticCtx);
     size_t dataLen;
-    const char* data = RedisModule_StringPtrLen(payload, &dataLen);
+    RedisModule_StringPtrLen(payload, &dataLen);
+
     char* buff_data = MR_ALLOC(ID_LEN);
     if (!buff_data) {
-        RedisModule_ThreadSafeContextUnlock(mr_staticCtx);
         return;
     }
+
+    RedisModule_ThreadSafeContextLock(mr_staticCtx);
+    const char* data = RedisModule_StringPtrLen(payload, &dataLen);
     memcpy(buff_data, data, ID_LEN);
     RedisModule_ThreadSafeContextUnlock(mr_staticCtx);
 
@@ -1129,15 +1135,19 @@ static Execution* MR_ExecutionDeserialize(mr_BufferReader* buffReader) {
 static void MR_RecieveExecution(void* pd) {
     RedisModuleString* payload = pd;
 
-    RedisModule_ThreadSafeContextLock(mr_staticCtx);
     size_t dataSize;
-    const char* data = RedisModule_StringPtrLen(payload, &dataSize);
+    RedisModule_StringPtrLen(payload, &dataSize);
+
     char* buff_data = MR_ALLOC(dataSize);
     if (!buff_data) {
+        RedisModule_ThreadSafeContextLock(mr_staticCtx);
         RedisModule_FreeString(NULL, payload);
         RedisModule_ThreadSafeContextUnlock(mr_staticCtx);
         return;
     }
+
+    RedisModule_ThreadSafeContextLock(mr_staticCtx);
+    const char* data = RedisModule_StringPtrLen(payload, &dataSize);
     memcpy(buff_data, data, dataSize);
     RedisModule_FreeString(NULL, payload);
     RedisModule_ThreadSafeContextUnlock(mr_staticCtx);