expose systemclock time to JS

Reviewed By: tadeuzagallo

Differential Revision: D2748749

fb-gh-sync-id: 4d1dbae61f69a07b7106cb57caff03cadfb85776

ReactAndroid/src/main/jni/react/JSCExecutor.cpp

@@ -9,6 +9,7 @@
 #include <folly/json.h>
 #include <folly/String.h>
 #include <jni/fbjni/Exceptions.h>
+#include <sys/time.h>
 #include "Value.h"
 #include "jni/OnLoad.h"
 
@@ -34,6 +35,9 @@ using fbsystrace::FbSystraceSection;
 #include <jsc_config_android.h>
 #endif
 
+static const int64_t NANOSECONDS_IN_SECOND = 1000000000LL;
+static const int64_t NANOSECONDS_IN_MILLISECOND = 1000000LL;
+
 using namespace facebook::jni;
 
 namespace facebook {
@@ -54,6 +58,13 @@ static JSValueRef nativeLoggingHook(
     size_t argumentCount,
     const JSValueRef arguments[],
     JSValueRef *exception);
+static JSValueRef nativePerformanceNow(
+    JSContextRef ctx,
+    JSObjectRef function,
+    JSObjectRef thisObject,
+    size_t argumentCount,
+    const JSValueRef arguments[],
+    JSValueRef *exception);
 
 static JSValueRef evaluateScriptWithJSC(
     JSGlobalContextRef ctx,
@@ -110,6 +121,7 @@ JSCExecutor::JSCExecutor(FlushImmediateCallback cb) :
   s_globalContextRefToJSCExecutor[m_context] = this;
   installGlobalFunction(m_context, "nativeFlushQueueImmediate", nativeFlushQueueImmediate);
   installGlobalFunction(m_context, "nativeLoggingHook", nativeLoggingHook);
+  installGlobalFunction(m_context, "nativePerformanceNow", nativePerformanceNow);
 
   #ifdef WITH_FB_JSC_TUNING
   configureJSCForAndroid();
@@ -283,4 +295,17 @@ static JSValueRef nativeLoggingHook(
   return JSValueMakeUndefined(ctx);
 }
 
+static JSValueRef nativePerformanceNow(
+    JSContextRef ctx,
+    JSObjectRef function,
+    JSObjectRef thisObject,
+    size_t argumentCount,
+    const JSValueRef arguments[], JSValueRef *exception) {
+  // This is equivalent to android.os.SystemClock.elapsedRealtime() in native
+  struct timespec now;
+  clock_gettime(CLOCK_MONOTONIC_RAW, &now);
+  int64_t nano = now.tv_sec * NANOSECONDS_IN_SECOND + now.tv_nsec;
+  return JSValueMakeNumber(ctx, (nano / (double)NANOSECONDS_IN_MILLISECOND));
+}
+
 } }