From 84b47b935a1c6fb99c986ed9df6d6866177016b3 Mon Sep 17 00:00:00 2001
From: Ryan Hamley <rshamley@gmail.com>
Date: Fri, 22 Jan 2021 14:41:24 -0800
Subject: [PATCH] Dedupe calls to performance.measure

---
 src/source/vector_tile_worker_source.js | 3 ++-
 src/util/performance.js                 | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/source/vector_tile_worker_source.js b/src/source/vector_tile_worker_source.js
index e642f598931..72c242875c6 100644
--- a/src/source/vector_tile_worker_source.js
+++ b/src/source/vector_tile_worker_source.js
@@ -192,7 +192,8 @@ class VectorTileWorkerSource implements WorkerSource {
             if (response.cacheControl) cacheControl.cacheControl = response.cacheControl;
 
             const resourceTiming = {};
-            if (perf) {
+            // because of two-phase tile loading, it's necessary to dedupe perf marking to avoid errors
+            if (perf && !perf._marksWereCleared()) {
                 const resourceTimingData = perf.finish();
                 // it's necessary to eval the result of getEntriesByName() here via parse/stringify
                 // late evaluation in the main thread causes TypeError: illegal invocation
diff --git a/src/util/performance.js b/src/util/performance.js
index d03a8e94170..e5548f4939d 100644
--- a/src/util/performance.js
+++ b/src/util/performance.js
@@ -178,6 +178,10 @@ export class RequestPerformance {
 
         performance.mark(this._marks.start);
     }
+    
+    _marksWereCleared() {
+        return performance.getEntriesByName(this._marks.start).length === 0;
+    }
 
     finish() {
         performance.mark(this._marks.end);