Fix a crash caused by improper management of async workers

src/bindings/text-buffer-wrapper.cc

@@ -623,6 +623,11 @@ void TextBufferWrapper::find_words_with_subsequence_in_range(const CallbackInfo
     }
 
     void OnWorkComplete(Napi::Env env, napi_status status) override {
+      {
+        std::lock_guard<std::mutex> guard(text_buffer_wrapper->outstanding_workers_mutex);
+        text_buffer_wrapper->outstanding_workers.erase(this);
+      }
+
       if (status == napi_cancelled) {
         Callback().Call({env.Null()});
       }
@@ -631,11 +636,6 @@ void TextBufferWrapper::find_words_with_subsequence_in_range(const CallbackInfo
     }
 
     void Execute() override {
-      {
-        std::lock_guard<std::mutex> guard(text_buffer_wrapper->outstanding_workers_mutex);
-        text_buffer_wrapper->outstanding_workers.erase(this);
-      }
-
       if (!snapshot) {
         return;
       }

test/js/text-buffer.test.js

@@ -13,6 +13,10 @@ const MAX_INT32 = 4294967296
 
 const isWindows = process.platform === 'win32'
 
+async function wait (ms) {
+  return new Promise(r => setTimeout(r, ms));
+}
+
 const encodings = [
   'big5hkscs',
   'cp850',
@@ -1261,6 +1265,25 @@ describe('TextBuffer', () => {
       return Promise.all(promises)
     })
 
+    it('doesn\'t crash when a job is cancelled', async () => {
+      function randomChar () {
+        const chars = "abcdefghijklmnopqrstuvwxyz ";
+        return chars[Math.floor(Math.random() * chars.length)];
+      }
+      let buffer = new TextBuffer(`lorem ipsum dolor sit amet, consecuetur adipiscing elit`)
+      // This test triggers a known segfault scenario in which a
+      // `FindWordsWithSubsequenceInRangeWorker` is created and then needs to
+      // be cancelled because of a subsequent call to `set_text_in_range`. Just
+      // like the test above, this one will either pass without making any
+      // assertions… or crash.
+      for (let k = 0; k < 100; k++) {
+        let ch = randomChar()
+        buffer.findWordsWithSubsequence('lor', '(){} :;,$@%', 20)
+        buffer.setTextInRange({ start: { row: 0, column: 8 }, end: { row: 0, column: 9 } }, ch)
+        await wait(Math.round(Math.random() * 20))
+      }
+    })
+
     it('resolves with all words matching the given query', () => {
       const buffer = new TextBuffer('banana bandana ban_ana bandaid band bNa\nbanana')
       return buffer.findWordsWithSubsequence('bna', '_', 4).then((result) => {