Do you know which exception is getting scheduled and causing V8 to return empty Maybes? I tried to run the test without the fix and it's always coming from one of these Check() calls for me:

This is the other exception, which doesn't occur that often, in fact I could try to devise a different test which exercises that path more often:

FATAL ERROR: v8::FromJust Maybe value is Nothing.
 1: 0xb57b90 node::Abort() [node]
 2: 0xa701b3 node::FatalError(char const*, char const*) [node]
 3: 0xd4388a v8::Utils::ReportApiFailure(char const*, char const*) [node]
 4: 0xb5bfed node::fs::FileHandle::CloseReq::Resolve() [node]
 5: 0xb5c170  [node]
 6: 0x1634dbd  [node]
 7: 0x1639596  [node]
 8: 0x164bcd4  [node]
 9: 0x1639ee8 uv_run [node]
10: 0xa95e45 node::SpinEventLoop(node::Environment*) [node]
11: 0xc22472 node::worker::Worker::Run() [node]
12: 0xc22a58  [node]
13: 0x7f765d46a609  [/lib/x86_64-linux-gnu/libpthread.so.0]
14: 0x7f765d38f163 clone [/lib/x86_64-linux-gnu/libc.so.6]
Aborted

And this is the 3rd one:

node[30432]: ../src/node_file-inl.h:160:node::fs::FSReqPromise<AliasedBufferT>::~FSReqPromise() [with AliasedBufferT = node::AliasedBufferBase<double, v8::Float64Array>]: Assertion `finished_' failed.
 1: 0xb57b90 node::Abort() [node]
 2: 0xb57c0e  [node]
 3: 0xb5288a  [node]
 4: 0xb5e74a node::fs::FSReqAfterScope::~FSReqAfterScope() [node]
 5: 0xb5f09e node::fs::AfterOpenFileHandle(uv_fs_s*) [node]
 6: 0x1634dbd  [node]
 7: 0x1639596  [node]
 8: 0x164bcd4  [node]
 9: 0x1639ee8 uv_run [node]
10: 0xa95e45 node::SpinEventLoop(node::Environment*) [node]
11: 0xc22472 node::worker::Worker::Run() [node]
12: 0xc22a58  [node]
13: 0x7fcbc059f609  [/lib/x86_64-linux-gnu/libpthread.so.0]
14: 0x7fcbc04c4163 clone [/lib/x86_64-linux-gnu/libc.so.6]
Aborted

@RaisinTen if you want to test it on your side, applying this patch to the current test makes the 2 other errors appear mostly all the time:

diff --git a/test/parallel/test-worker-fshandles-closed.js b/test/parallel/test-worker-fshandles-closed.js
index 730b5fc3b1..e3c62bba4a 100644
--- a/test/parallel/test-worker-fshandles-closed.js
+++ b/test/parallel/test-worker-fshandles-closed.js
@@ -49,7 +49,7 @@ if (isMainThread) {
   }
 
   open_close_ok().then(common.mustCall());
-  open_close_nok().then(common.mustCall());
+  open_close_ok().then(common.mustCall());
 
   parentPort.postMessage('terminate');
 }

Sure, feel free to add more tests for those paths though I don't think it's strictly necessary for this PR. The crash sites are indeed spread over multiple places. However, I was curious to know which JS exception (not C++ crash) caused this. Do worker threads throw an exception if we interact with the isolate during termination? If so, what's the source?

Tbh, I was curious to know why pending exceptions caused v8::Object::Set() to crash only sometimes because I noticed some unexpected behavior which I thought was a bug in V8 (reported in https://crbug.com/v8/12839) but it seems we do some exception catching magic.

To answer my question, this crashes because of this exception -

CI: https://ci.nodejs.org/job/node-test-pull-request/44655/

CI: https://ci.nodejs.org/job/node-test-pull-request/44668/

- Loading data for nodejs/node/pull/42910
✔  Done loading data for nodejs/node/pull/42910
----------------------------------- PR info ------------------------------------
Title      fs: don't end fs promises on Isolate termination (#42910)
Author     Santiago Gimeno  (@santigimeno)
Branch     santigimeno:santi/some_filehandle_fixes -> nodejs:main
Labels     c++, fs, author ready, needs-ci
Commits    1
 - fs: don't end fs promises on Isolate termination
Committers 1
 - Santiago Gimeno 
PR-URL: https://github.com/nodejs/node/pull/42910
Fixes: https://github.com/nodejs/node/issues/42829
Reviewed-By: Antoine du Hamel 
Reviewed-By: Darshan Sen 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/42910
Fixes: https://github.com/nodejs/node/issues/42829
Reviewed-By: Antoine du Hamel 
Reviewed-By: Darshan Sen 
--------------------------------------------------------------------------------
   ⚠  Commits were pushed since the last review:
   ⚠  - fs: don't end fs promises on Isolate termination
   ℹ  This PR was created on Fri, 29 Apr 2022 14:06:18 GMT
   ✔  Approvals: 2
   ✔  - Antoine du Hamel (@aduh95) (TSC): https://github.com/nodejs/node/pull/42910#pullrequestreview-958012346
   ✔  - Darshan Sen (@RaisinTen) (TSC): https://github.com/nodejs/node/pull/42910#pullrequestreview-962848317
   ✔  Last GitHub CI successful
   ℹ  Last Full PR CI on 2022-06-18T00:22:32Z: https://ci.nodejs.org/job/node-test-pull-request/44668/
- Querying data for job/node-test-pull-request/44668/
   ✔  Last Jenkins CI successful
--------------------------------------------------------------------------------
   ✔  Aborted `git node land` session in /home/runner/work/node/node/.ncu

Landed in 4c077b0

This has introduced a flake in the CI: #43499 should we revert this?

This has introduced a flake in the CI: #43499 should we revert this?

Please, hold on a bit. I'm investigating this and post a fix shortly.