From b3352cfba4982dd9c6e78e7609ff2e9e92582eed Mon Sep 17 00:00:00 2001
From: Rich Trott <rtrott@gmail.com>
Date: Mon, 2 Aug 2021 21:41:19 -0700
Subject: [PATCH] debugger: prevent simultaneous heap snapshots
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Fixes: https://github.com/nodejs/node/issues/39555

PR-URL: https://github.com/nodejs/node/pull/39638
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
---
 lib/internal/debugger/inspect_repl.js          | 11 ++++++++++-
 test/sequential/test-debugger-heap-profiler.js |  4 ++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/internal/debugger/inspect_repl.js b/lib/internal/debugger/inspect_repl.js
index a93a8dfecf2720..401887cbda5c74 100644
--- a/lib/internal/debugger/inspect_repl.js
+++ b/lib/internal/debugger/inspect_repl.js
@@ -325,6 +325,7 @@ function createRepl(inspector) {
   const history = { control: [], debug: [] };
   const watchedExpressions = [];
   const knownBreakpoints = [];
+  let heapSnapshotPromise = null;
   let pauseOnExceptionState = 'none';
   let lastCommand;
 
@@ -961,7 +962,13 @@ function createRepl(inspector) {
       },
 
       takeHeapSnapshot(filename = 'node.heapsnapshot') {
-        return new Promise((resolve, reject) => {
+        if (heapSnapshotPromise) {
+          print(
+            'Cannot take heap snapshot because another snapshot is in progress.'
+          );
+          return heapSnapshotPromise;
+        }
+        heapSnapshotPromise = new Promise((resolve, reject) => {
           const absoluteFile = Path.resolve(filename);
           const writer = FS.createWriteStream(absoluteFile);
           let sizeWritten = 0;
@@ -983,6 +990,7 @@ function createRepl(inspector) {
             writer.end(() => {
               teardown();
               print(`Wrote snapshot: ${absoluteFile}`);
+              heapSnapshotPromise = null;
               resolve();
             });
           }
@@ -1006,6 +1014,7 @@ function createRepl(inspector) {
             HeapProfiler.takeHeapSnapshot({ reportProgress: true }),
             onResolve, onReject);
         });
+        return heapSnapshotPromise;
       },
 
       get watchers() {
diff --git a/test/sequential/test-debugger-heap-profiler.js b/test/sequential/test-debugger-heap-profiler.js
index 6ba55e8078348f..69be07a6f9c517 100644
--- a/test/sequential/test-debugger-heap-profiler.js
+++ b/test/sequential/test-debugger-heap-profiler.js
@@ -32,6 +32,10 @@ const filename = 'node.heapsnapshot';
     .then(() => cli.waitForPrompt())
     .then(() => cli.command('takeHeapSnapshot()'))
     .then(() => JSON.parse(readFileSync(filename, 'utf8')))
+    // Check that two simultaneous snapshots don't step all over each other.
+    // Refs: https://github.com/nodejs/node/issues/39555
+    .then(() => cli.command('takeHeapSnapshot(); takeHeapSnapshot()'))
+    .then(() => JSON.parse(readFileSync(filename, 'utf8')))
     .then(() => cli.quit())
     .then(null, onFatal);
 }