process: allow monitoring uncaughtException

doc/api/process.md

@@ -262,6 +262,10 @@ 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
+`'uncaughtExceptionMonitor'` listener.
+
 #### Warning: Using `'uncaughtException'` correctly
 
 `'uncaughtException'` is a crude mechanism for exception handling
@@ -289,6 +293,34 @@ To restart a crashed application in a more reliable way, whether
 in a separate process to detect application failures and recover or restart as
 needed.
 
+### Event: `'uncaughtExceptionMonitor'`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `err` {Error} The uncaught exception.
+* `origin` {string} Indicates if the exception originates from an unhandled
+  rejection or from synchronous errors. Can either be `'uncaughtException'` or
+  `'unhandledRejection'`.
+
+The `'uncaughtExceptionMonitor'` event is emitted before an
+`'uncaughtException'` event is emitted or a hook installed via
+[`process.setUncaughtExceptionCaptureCallback()`][] is called.
+
+Installing an `'uncaughtExceptionMonitor'` listener does not change the behavior
+once an `'uncaughtException'` event is emitted. The process will
+still crash if no `'uncaughtException'` listener is installed.
+
+```js
+process.on('uncaughtExceptionMonitor', (err, origin) => {
+  MyMonitoringTool.logSync(err, origin);
+});
+
+// Intentionally cause an exception, but don't catch it.
+nonexistentFunc();
+// Still crashes Node.js
+```
+
 ### Event: `'unhandledRejection'`
 <!-- YAML
 added: v1.4.1

lib/internal/process/execution.js

@@ -159,6 +159,7 @@ function createOnGlobalUncaughtException() {
     }
 
     const type = fromPromise ? 'unhandledRejection' : 'uncaughtException';
+    process.emit('uncaughtExceptionMonitor', er, type);
     if (exceptionHandlerState.captureFn !== null) {
       exceptionHandlerState.captureFn(er);
     } else if (!process.emit('uncaughtException', er, type)) {

test/fixtures/uncaught-exceptions/uncaught-monitor1.js

@@ -0,0 +1,10 @@
+'use strict';
+
+// Keep the event loop alive.
+setTimeout(() => {}, 1e6);
+
+process.on('uncaughtExceptionMonitor', (err) => {
+  console.log(`Monitored: ${err.message}`);
+});
+
+throw new Error('Shall exit');

test/fixtures/uncaught-exceptions/uncaught-monitor2.js

@@ -0,0 +1,11 @@
+'use strict';
+
+// Keep the event loop alive.
+setTimeout(() => {}, 1e6);
+
+process.on('uncaughtExceptionMonitor', (err) => {
+  console.log(`Monitored: ${err.message}, will throw now`);
+  missingFunction();
+});
+
+throw new Error('Shall exit');

test/parallel/test-process-uncaught-exception-monitor.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { execFile } = require('child_process');
+const fixtures = require('../common/fixtures');
+
+{
+  // Verify exit behavior is unchanged
+  const fixture = fixtures.path('uncaught-exceptions', 'uncaught-monitor1.js');
+  execFile(
+    process.execPath,
+    [fixture],
+    common.mustCall((err, stdout, stderr) => {
+      assert.strictEqual(err.code, 1);
+      assert.strictEqual(Object.getPrototypeOf(err).name, 'Error');
+      assert.strictEqual(stdout, 'Monitored: Shall exit\n');
+      const errLines = stderr.trim().split(/[\r\n]+/);
+      const errLine = errLines.find((l) => /^Error/.exec(l));
+      assert.strictEqual(errLine, 'Error: Shall exit');
+    })
+  );
+}
+
+{
+  // Verify exit behavior is unchanged
+  const fixture = fixtures.path('uncaught-exceptions', 'uncaught-monitor2.js');
+  execFile(
+    process.execPath,
+    [fixture],
+    common.mustCall((err, stdout, stderr) => {
+      assert.strictEqual(err.code, 7);
+      assert.strictEqual(Object.getPrototypeOf(err).name, 'Error');
+      assert.strictEqual(stdout, 'Monitored: Shall exit, will throw now\n');
+      const errLines = stderr.trim().split(/[\r\n]+/);
+      const errLine = errLines.find((l) => /^ReferenceError/.exec(l));
+      assert.strictEqual(
+        errLine,
+        'ReferenceError: missingFunction is not defined'
+      );
+    })
+  );
+}
+
+const theErr = new Error('MyError');
+
+process.on(
+  'uncaughtExceptionMonitor',
+  common.mustCall((err, origin) => {
+    assert.strictEqual(err, theErr);
+    assert.strictEqual(origin, 'uncaughtException');
+  }, 2)
+);
+
+process.on('uncaughtException', common.mustCall((err, origin) => {
+  assert.strictEqual(origin, 'uncaughtException');
+  assert.strictEqual(err, theErr);
+}));
+
+process.nextTick(common.mustCall(() => {
+  // Test with uncaughtExceptionCaptureCallback installed
+  process.setUncaughtExceptionCaptureCallback(common.mustCall(
+    (err) => assert.strictEqual(err, theErr))
+  );
+
+  throw theErr;
+}));
+
+throw theErr;