From 3885c19481fdff1c905e988d5d4cf7a546af4902 Mon Sep 17 00:00:00 2001
From: medjed02 <medjed02dev@gmail.com>
Date: Tue, 10 Nov 2026 19:16:19 +0300
Subject: [PATCH] Stop the pool optimizer in stopWorkers()

stopWorkers() stops every background worker except the pool optimizer.
shutDown() relies on it before saving the cache state, so with the pool
optimizer enabled the optimizer thread can still resize pools while the
state is being serialized; the destructor has the same window until the
PoolOptimizer member itself is destroyed.

Test: a counting PoolOptimizeStrategy is no longer called after
stopWorkers() returns.
---
 cachelib/allocator/CacheAllocator.h           |  1 +
 .../tests/SimplePoolOptimizationTest.cpp      |  4 +++
 .../tests/SimplePoolOptimizationTest.h        | 31 +++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/cachelib/allocator/CacheAllocator.h b/cachelib/allocator/CacheAllocator.h
index b485a5fbab..4e98b3e613 100644
--- a/cachelib/allocator/CacheAllocator.h
+++ b/cachelib/allocator/CacheAllocator.h
@@ -6359,6 +6359,7 @@ folly::IOBufQueue CacheAllocator<CacheTrait>::saveStateToIOBuf() {
 template <typename CacheTrait>
 bool CacheAllocator<CacheTrait>::stopWorkers(std::chrono::seconds timeout) {
   bool success = true;
+  success &= stopPoolOptimizer(timeout);
   success &= stopPoolRebalancer(timeout);
   success &= stopPoolResizer(timeout);
   success &= stopMemMonitor(timeout);
diff --git a/cachelib/allocator/tests/SimplePoolOptimizationTest.cpp b/cachelib/allocator/tests/SimplePoolOptimizationTest.cpp
index 63b567f0ed..e01c3d59c4 100644
--- a/cachelib/allocator/tests/SimplePoolOptimizationTest.cpp
+++ b/cachelib/allocator/tests/SimplePoolOptimizationTest.cpp
@@ -29,6 +29,10 @@ TYPED_TEST(SimplePoolOptimizationTest, PoolOptimizerBasic) {
   this->testPoolOptimizerBasic();
 }
 
+TYPED_TEST(SimplePoolOptimizationTest, StopWorkersStopsPoolOptimizer) {
+  this->testStopWorkersStopsPoolOptimizer();
+}
+
 } // namespace tests
 } // namespace cachelib
 } // namespace facebook
diff --git a/cachelib/allocator/tests/SimplePoolOptimizationTest.h b/cachelib/allocator/tests/SimplePoolOptimizationTest.h
index 2313ef4f6e..13c77dd851 100644
--- a/cachelib/allocator/tests/SimplePoolOptimizationTest.h
+++ b/cachelib/allocator/tests/SimplePoolOptimizationTest.h
@@ -19,7 +19,10 @@
 #include <folly/Random.h>
 #include <gtest/gtest.h>
 
+#include <atomic>
+#include <chrono>
 #include <future>
+#include <thread>
 
 #include "cachelib/allocator/CCacheAllocator.h"
 #include "cachelib/allocator/PoolOptimizer.h"
@@ -85,6 +88,34 @@ struct SimplePoolOptimizeStrategy : public PoolOptimizeStrategy {
 template <typename AllocatorT>
 class SimplePoolOptimizationTest : public testing::Test {
  public:
+  void testStopWorkersStopsPoolOptimizer() {
+    struct CountingStrategy : public PoolOptimizeStrategy {
+      std::atomic<int> calls{0};
+
+     protected:
+      PoolOptimizeContext pickVictimAndReceiverRegularPoolsImpl(
+          const CacheBase&) override {
+        ++calls;
+        return kNoOpContext;
+      }
+    };
+    auto strategy = std::make_shared<CountingStrategy>();
+    typename AllocatorT::Config config;
+    config.setCacheSize(30 * Slab::kSize);
+    config.enablePoolOptimizer(strategy, std::chrono::seconds{1},
+                               std::chrono::seconds{1}, 1);
+    AllocatorT alloc(config);
+    for (int i = 0; i < 100 && strategy->calls == 0; ++i) {
+      std::this_thread::sleep_for(std::chrono::milliseconds{100});
+    }
+    ASSERT_GT(strategy->calls.load(), 0);
+
+    ASSERT_TRUE(alloc.stopWorkers());
+    const int calls = strategy->calls.load();
+    std::this_thread::sleep_for(std::chrono::seconds{2});
+    EXPECT_EQ(calls, strategy->calls.load());
+  }
+
   void testPoolOptimizerBasic() {
     typename AllocatorT::Config config;
     config.setCacheSize(30 * Slab::kSize);