gc: fix instance allocation counting

A class destructor is not called if an exception is thrown when
executing the constructor. This caused an issue where if an error
occured during construction of NSFW objects, the instance coutn would
never be decremented.

This commit moves the increment step at the end of the constructor,
after which nothing can error out.

Signed-off-by: Paul Maréchal <[email protected]>

Author: paul-marechal

js/spec/index-spec.js

@@ -684,6 +684,15 @@ describe('Node Sentinel File Watcher', function() {
   describe('Garbage collection', function() {
     it('can garbage collect all instances', async function () {
       this.timeout(60000);
+      let threw = false;
+      try {
+        // Try to get an error coming from the C++ constructor by passing a bad callback
+        await nsfw(workDir, () => {}, { errorCallback: 'not a callback' });
+      } catch (e) {
+        threw = true;
+      } if (!threw) {
+        assert.fail('nsfw must throw when provided a bad callback');
+      }
       while (nsfw.getAllocatedInstanceCount() > 0) {
         global.gc();
         await sleep(0);

src/NSFW.cpp

@@ -12,10 +12,6 @@ NSFW::NSFW(const Napi::CallbackInfo &info):
   mPath(""),
   mRunning(false)
 {
-  if (gcEnabled) {
-    instanceCount++;
-  }
-
   auto env = info.Env();
   if (info.Length() < 1 || !info[0].IsString()) {
     throw Napi::TypeError::New(env, "Must pass a string path as the first argument to NSFW.");
@@ -71,6 +67,10 @@ NSFW::NSFW(const Napi::CallbackInfo &info):
       1
     );
   }
+
+  if (gcEnabled) {
+    instanceCount++;
+  }
 }
 
 NSFW::~NSFW() {