[JSC] Add activeJSGlobalObjectSignpostIntervalCount

https://bugs.webkit.org/show_bug.cgi?id=265003
rdar://118545511

Reviewed by Mark Lam.

Add activeJSGlobalObjectSignpostIntervalCount global variable, which offers counter of active JSGlobalObject signpost intervals.
This is really useful since we can know whether we are inside signpost interval or not quickly by checking this number.

* Source/JavaScriptCore/runtime/JSGlobalObject.cpp:
(JSC::JSC_DEFINE_HOST_FUNCTION):

Canonical link: https://commits.webkit.org/270864@main

Source/JavaScriptCore/runtime/JSCJSValue.h

@@ -134,6 +134,9 @@ enum class SourceCodeRepresentation : uint8_t {
 };
 
 extern JS_EXPORT_PRIVATE const ASCIILiteral SymbolCoercionError;
+#if HAVE(OS_SIGNPOST)
+extern JS_EXPORT_PRIVATE std::atomic<unsigned> activeJSGlobalObjectSignpostIntervalCount;
+#endif
 
 class JSValue {
     friend struct EncodedJSValueHashTraits;

Source/JavaScriptCore/runtime/JSGlobalObject.cpp

@@ -522,6 +522,8 @@ static String asSignpostString(JSGlobalObject* globalObject, JSValue v)
     return v.toWTFString(globalObject);
 }
 
+std::atomic<unsigned> activeJSGlobalObjectSignpostIntervalCount { 0 };
+
 JSC_DEFINE_HOST_FUNCTION(signpostStart, (JSGlobalObject* globalObject, CallFrame* callFrame))
 {
     VM& vm = globalObject->vm();
@@ -530,6 +532,7 @@ JSC_DEFINE_HOST_FUNCTION(signpostStart, (JSGlobalObject* globalObject, CallFrame
     auto message = asSignpostString(globalObject, callFrame->argument(0));
     RETURN_IF_EXCEPTION(scope, EncodedJSValue());
 
+    ++activeJSGlobalObjectSignpostIntervalCount;
     os_signpost_interval_begin(WTFSignpostLogHandle(), os_signpost_id_make_with_pointer(WTFSignpostLogHandle(), globalObject), "JSGlobalObject signpost", "%" PUBLIC_LOG_STRING, message.ascii().data());
 
     return JSValue::encode(jsUndefined());
@@ -544,6 +547,7 @@ JSC_DEFINE_HOST_FUNCTION(signpostStop, (JSGlobalObject* globalObject, CallFrame*
     RETURN_IF_EXCEPTION(scope, EncodedJSValue());
 
     os_signpost_interval_end(WTFSignpostLogHandle(), os_signpost_id_make_with_pointer(WTFSignpostLogHandle(), globalObject), "JSGlobalObject signpost", "%" PUBLIC_LOG_STRING, message.ascii().data());
+    --activeJSGlobalObjectSignpostIntervalCount;
 
     return JSValue::encode(jsUndefined());
 }