fix: Use thread_local storage to increment getCurrentThreadId() (#…

…170)

cpp/WKTJsiWorkletApi.h

@@ -3,7 +3,6 @@
 #include <jsi/jsi.h>
 
 #include <memory>
-#include <sstream>
 #include <string>
 #include <thread>
 #include <vector>
@@ -109,13 +108,14 @@ class JsiWorkletApi : public JsiHostObject {
                        "deprecated in favor of context.createRunAsync(..) or "
                        "context.runAsync(..) - please migrate to the new API!");
   }
-    
+
   JSI_HOST_FUNCTION(getCurrentThreadId) {
-    std::thread::id threadId = std::this_thread::get_id();
-    std::stringstream stream;
-    stream << threadId;
-    std::string string = stream.str();
-    return jsi::String::createFromUtf8(runtime, string);
+    static int threadCounter = 0;
+    static thread_local int thisThreadId = -1;
+    if (thisThreadId == -1) {
+      thisThreadId = threadCounter++;
+    }
+    return jsi::Value(thisThreadId);
   }
 
   JSI_HOST_FUNCTION(__jsi_is_array) {

example/Tests/worklet-tests.ts

@@ -121,7 +121,7 @@ export const worklet_tests = {
   },
   check_thread_id_exists: () => {
     const threadId = Worklets.getCurrentThreadId();
-    return ExpectValue(threadId.length > 0, true);
+    return ExpectValue(Number.isSafeInteger(threadId), true);
   },
   check_thread_id_consecutive_calls_are_equal: () => {
     const first = Worklets.getCurrentThreadId();

src/types.ts

@@ -146,9 +146,12 @@ export interface IWorkletNativeApi {
   runOnJS: <T>(func: () => T) => Promise<T>;
 
   /**
-   * Returns the current C++ Thread ID this method was called on.
+   * Returns a unique identifier for the Thread this method is called on.
+   *
+   * Thread-IDs start at 0 and use `thread_local` storage to store their IDs
+   * which are incremented everytime a new Thread calls `getCurrentThreadId()`.
    */
-  getCurrentThreadId(): string;
+  getCurrentThreadId(): number;
   /**
    * Get the default Worklet context.
    */