perf_hooks: copy shared data before importing histograms

src/histogram.cc

@@ -3211,6 +3211,15 @@ void HistogramImpl::DoImport(const FunctionCallbackInfo<Value>& args) {
       static_cast<const uint8_t*>(backing->Data()) + input->ByteOffset();
   size_t len = input->ByteLength();
 
+  // Another thread can write to a SharedArrayBuffer while it is parsed, so
+  // parse a private copy instead.
+  std::unique_ptr<uint8_t[]> data_copy;
+  if (input->Buffer()->IsSharedArrayBuffer() && len > 0) {
+    data_copy = std::make_unique_for_overwrite<uint8_t[]>(len);
+    memcpy(data_copy.get(), data, len);
+    data = data_copy.get();
+  }
+
   auto histogram = Histogram::Import(data, len);
   if (!histogram) {
     THROW_ERR_INVALID_ARG_VALUE(env, "Invalid histogram export data");

test/parallel/test-perf-hooks-histogram-import-shared.js

@@ -0,0 +1,33 @@
+'use strict';
+
+require('../common');
+const assert = require('node:assert');
+const { createHistogram, importHistogram } = require('node:perf_hooks');
+const kInvalid = { code: 'ERR_INVALID_ARG_VALUE' };
+
+{
+  // Data in a SharedArrayBuffer, including a sliced view, imports the same way
+  // as data in an ArrayBuffer.
+  const h = createHistogram();
+  h.record(1);
+  h.record(42);
+  h.record(1000);
+  const exported = h.export();
+
+  for (const offset of [0, 3]) {
+    const sab = new SharedArrayBuffer(exported.length + offset + 5);
+    new Uint8Array(sab).fill(0xff);
+    const view = new Uint8Array(sab, offset, exported.length);
+    view.set(exported);
+    const imported = importHistogram(view);
+    assert.deepStrictEqual(imported.export(), exported);
+
+    // Later writes do not change the imported histogram.
+    view.fill(0);
+    assert.deepStrictEqual(imported.export(), exported);
+    assert.throws(() => importHistogram(view), kInvalid);
+  }
+
+  assert.throws(
+    () => importHistogram(new Uint8Array(new SharedArrayBuffer(0))), kInvalid);
+}