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process: allow monitoring uncaughtException #31257

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28 changes: 28 additions & 0 deletions doc/api/process.md
Original file line number Diff line number Diff line change
Expand Up @@ -262,6 +262,20 @@ nonexistentFunc();
console.log('This will not run.');
```

It is possible to monitor `'uncaughtException'` events without overriding the
default behavior to exit the process by installing a listener using the symbol
`uncaughtExceptionMonitor`.

```js
process.on(process.uncaughtExceptionMonitor, (err, origin) => {
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MyMonitoringTool.logSync(err, origin);
});

// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
// Still crashes Node.js
```

#### Warning: Using `'uncaughtException'` correctly

`'uncaughtException'` is a crude mechanism for exception handling
Expand Down Expand Up @@ -2320,6 +2334,20 @@ documentation for the [`'warning'` event][process_warning] and the
[`emitWarning()` method][process_emit_warning] for more information about this
flag's behavior.

## `process.uncaughtExceptionMonitor`
<!-- YAML
added: REPLACEME
-->

This symbol shall be used to install a listener for only monitoring
`'uncaughtException'` events. Listeners installed using this symbol are called
before the regular `'uncaughtException'` listeners and before a hook
installed via [`process.setUncaughtExceptionCaptureCallback()`][].

Installing a listener using this symbol does not change the behavior once an
`'uncaughtException'` event is emitted, therefore the process will still crash
if no regular `'uncaughtException'` listener is installed.

## `process.umask([mask])`
<!-- YAML
added: v0.1.19
Expand Down
9 changes: 8 additions & 1 deletion lib/internal/bootstrap/node.js
Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,8 @@ ObjectDefineProperty(process, 'features', {
const {
onGlobalUncaughtException,
setUncaughtExceptionCaptureCallback,
hasUncaughtExceptionCaptureCallback
hasUncaughtExceptionCaptureCallback,
kUncaughtExceptionMonitor
} = require('internal/process/execution');

// For legacy reasons this is still called `_fatalException`, even
Expand All @@ -220,6 +221,12 @@ ObjectDefineProperty(process, 'features', {
setUncaughtExceptionCaptureCallback;
process.hasUncaughtExceptionCaptureCallback =
hasUncaughtExceptionCaptureCallback;
ObjectDefineProperty(process, 'uncaughtExceptionMonitor', {
value: kUncaughtExceptionMonitor,
writable: false,
configurable: true,
enumerable: true
});
}

const { emitWarning } = require('internal/process/warning');
Expand Down
7 changes: 6 additions & 1 deletion lib/internal/process/execution.js
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
const {
JSONStringify,
PromiseResolve,
Symbol,
} = primordials;

const path = require('path');
Expand All @@ -27,6 +28,8 @@ const {
// communication with JS.
const { shouldAbortOnUncaughtToggle } = internalBinding('util');

const kUncaughtExceptionMonitor = Symbol('process.uncaughtExceptionMonitor');

function tryGetCwd() {
try {
return process.cwd();
Expand Down Expand Up @@ -159,6 +162,7 @@ function createOnGlobalUncaughtException() {
}

const type = fromPromise ? 'unhandledRejection' : 'uncaughtException';
process.emit(kUncaughtExceptionMonitor, er, type);
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if (exceptionHandlerState.captureFn !== null) {
exceptionHandlerState.captureFn(er);
} else if (!process.emit('uncaughtException', er, type)) {
Expand Down Expand Up @@ -214,5 +218,6 @@ module.exports = {
evalScript,
onGlobalUncaughtException: createOnGlobalUncaughtException(),
setUncaughtExceptionCaptureCallback,
hasUncaughtExceptionCaptureCallback
hasUncaughtExceptionCaptureCallback,
kUncaughtExceptionMonitor
};
35 changes: 35 additions & 0 deletions test/parallel/test-process-uncaught-exception-monitor.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
'use strict';

const common = require('../common');
const assert = require('assert');

const theErr = new Error('MyError');

process.on(
process.uncaughtExceptionMonitor,
common.mustCall(function onUncaughtExceptionMonitor(err, origin) {
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assert.strictEqual(err, theErr);
assert.strictEqual(origin, 'uncaughtException');
}, 2)
);

process.on('uncaughtException', common.mustCall(
function onUncaughtException(err, origin) {
assert.strictEqual(origin, 'uncaughtException');
assert.strictEqual(err, theErr);
})
);

process.nextTick(common.mustCall(
function withExceptionCaptureCallback() {
process.setUncaughtExceptionCaptureCallback(common.mustCall(
function uncaughtExceptionCaptureCallback(err) {
assert.strictEqual(err, theErr);
})
);

throw theErr;
})
);

throw theErr;