From f8c306de305a72dbf8a4a9ad386b4816fcbc9922 Mon Sep 17 00:00:00 2001
From: Antonio SJ Musumeci <trapexit@spawn.link>
Date: Fri, 13 Mar 2026 14:15:40 -0500
Subject: [PATCH] Improve thread pool

---
 tests/tests.cpp                          | 536 +++++++++++++++++++++++
 vendored/libfuse/include/thread_pool.hpp |   2 +-
 2 files changed, 537 insertions(+), 1 deletion(-)

diff --git a/tests/tests.cpp b/tests/tests.cpp
index 6ca5b514..714da80e 100644
--- a/tests/tests.cpp
+++ b/tests/tests.cpp
@@ -6,9 +6,27 @@
 
 #include <atomic>
 #include <chrono>
+#include <future>
+#include <mutex>
 #include <numeric>
 #include <thread>
 
+template<typename Predicate>
+bool
+wait_until(Predicate pred_,
+           const int timeout_ms_ = 2000)
+{
+  for(int i = 0; i < timeout_ms_; ++i)
+    {
+      if(pred_())
+        return true;
+
+      std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    }
+
+  return pred_();
+}
+
 void
 test_nop()
 {
@@ -998,6 +1016,511 @@ test_tp_work_ordering_single_thread()
     TEST_CHECK(results[i] == i);
 }
 
+void
+test_tp_try_enqueue_work_fails_when_full()
+{
+  ThreadPool tp(1, 1, "test.tewfull");
+
+  std::atomic<bool> release{false};
+  std::atomic<bool> worker_started{false};
+  std::atomic<int> ran{0};
+
+  tp.enqueue_work([&release, &worker_started, &ran]()
+    {
+      worker_started.store(true);
+      while(!release.load())
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+      ran.fetch_add(1);
+    });
+
+  TEST_CHECK(wait_until([&worker_started](){ return worker_started.load(); }));
+
+  tp.enqueue_work([&ran](){ ran.fetch_add(1); });
+
+  bool ok = tp.try_enqueue_work([&ran](){ ran.fetch_add(1); });
+  TEST_CHECK(!ok);
+
+  release.store(true);
+
+  TEST_CHECK(wait_until([&ran](){ return ran.load() == 2; }));
+  TEST_CHECK(ran.load() == 2);
+}
+
+void
+test_tp_try_enqueue_work_for_times_out_when_full()
+{
+  ThreadPool tp(1, 1, "test.tewftimeout");
+
+  std::atomic<bool> release{false};
+  std::atomic<bool> worker_started{false};
+  std::atomic<int> ran{0};
+
+  tp.enqueue_work([&release, &worker_started, &ran]()
+    {
+      worker_started.store(true);
+      while(!release.load())
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+      ran.fetch_add(1);
+    });
+
+  TEST_CHECK(wait_until([&worker_started](){ return worker_started.load(); }));
+
+  tp.enqueue_work([&ran](){ ran.fetch_add(1); });
+
+  auto start = std::chrono::steady_clock::now();
+  bool ok = tp.try_enqueue_work_for(20000, [&ran](){ ran.fetch_add(1); });
+  auto end = std::chrono::steady_clock::now();
+
+  TEST_CHECK(!ok);
+
+  auto elapsed_us =
+    std::chrono::duration_cast<std::chrono::microseconds>(end - start).count();
+  TEST_CHECK(elapsed_us >= 10000);
+
+  release.store(true);
+
+  TEST_CHECK(wait_until([&ran](){ return ran.load() == 2; }));
+  TEST_CHECK(ran.load() == 2);
+}
+
+void
+test_tp_enqueue_work_blocks_until_slot_available()
+{
+  ThreadPool tp(1, 1, "test.ewblocks");
+
+  std::atomic<bool> release{false};
+  std::atomic<bool> worker_started{false};
+  std::atomic<bool> producer_returned{false};
+  std::atomic<int> ran{0};
+
+  tp.enqueue_work([&release, &worker_started, &ran]()
+    {
+      worker_started.store(true);
+      while(!release.load())
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+      ran.fetch_add(1);
+    });
+
+  TEST_CHECK(wait_until([&worker_started](){ return worker_started.load(); }));
+
+  tp.enqueue_work([&ran](){ ran.fetch_add(1); });
+
+  std::thread producer([&tp, &ran, &producer_returned]()
+    {
+      tp.enqueue_work([&ran](){ ran.fetch_add(1); });
+      producer_returned.store(true);
+    });
+
+  std::this_thread::sleep_for(std::chrono::milliseconds(20));
+  TEST_CHECK(!producer_returned.load());
+
+  release.store(true);
+
+  TEST_CHECK(wait_until([&producer_returned](){ return producer_returned.load(); }));
+  producer.join();
+
+  TEST_CHECK(wait_until([&ran](){ return ran.load() == 3; }));
+  TEST_CHECK(ran.load() == 3);
+}
+
+void
+test_tp_worker_nonstd_exception_no_crash()
+{
+  ThreadPool tp(2, 4, "test.nsexc");
+
+  tp.enqueue_work([](){ throw 7; });
+
+  std::atomic<bool> ran{false};
+  tp.enqueue_work([&ran](){ ran.store(true); });
+
+  TEST_CHECK(wait_until([&ran](){ return ran.load(); }));
+  TEST_CHECK(ran.load());
+}
+
+void
+test_tp_remove_thread_under_load()
+{
+  ThreadPool tp(4, 64, "test.rmuload");
+
+  std::atomic<int> counter{0};
+  const int N = 300;
+
+  for(int i = 0; i < N; ++i)
+    tp.enqueue_work([&counter]()
+      {
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        counter.fetch_add(1);
+      });
+
+  int rv1 = -1;
+  int rv2 = -1;
+
+  std::thread remover([&tp, &rv1, &rv2]()
+    {
+      rv1 = tp.remove_thread();
+      rv2 = tp.remove_thread();
+    });
+
+  remover.join();
+
+  TEST_CHECK(rv1 == 0);
+  TEST_CHECK(rv2 == 0);
+  TEST_CHECK(tp.threads().size() == 2);
+
+  TEST_CHECK(wait_until([&counter, N](){ return counter.load() == N; }, 10000));
+  TEST_CHECK(counter.load() == N);
+
+  std::atomic<bool> post_ok{false};
+  tp.enqueue_work([&post_ok](){ post_ok.store(true); });
+  TEST_CHECK(wait_until([&post_ok](){ return post_ok.load(); }));
+}
+
+void
+test_tp_set_threads_concurrent_with_enqueue()
+{
+  ThreadPool tp(3, 128, "test.stcwe");
+
+  const int PRODUCERS = 4;
+  const int PER_PRODUCER = 150;
+  const int TOTAL = PRODUCERS * PER_PRODUCER;
+  std::atomic<int> counter{0};
+
+  std::atomic<bool> producers_done{false};
+  std::atomic<int> resize_calls{0};
+
+  std::thread resizer([&tp, &producers_done, &resize_calls]()
+    {
+      int i = 0;
+      while(!producers_done.load())
+        {
+          std::size_t count = ((i % 2) == 0 ? 2 : 6);
+          int rv = tp.set_threads(count);
+          if(rv == 0)
+            resize_calls.fetch_add(1);
+          ++i;
+        }
+    });
+
+  std::vector<std::thread> producers;
+  for(int p = 0; p < PRODUCERS; ++p)
+    {
+      producers.emplace_back([&tp, &counter]()
+        {
+          auto ptok = tp.ptoken();
+          for(int i = 0; i < PER_PRODUCER; ++i)
+            tp.enqueue_work(ptok, [&counter](){ counter.fetch_add(1); });
+        });
+    }
+
+  for(auto &t : producers)
+    t.join();
+
+  producers_done.store(true);
+  resizer.join();
+
+  TEST_CHECK(resize_calls.load() > 0);
+  TEST_CHECK(wait_until([&counter, TOTAL](){ return counter.load() == TOTAL; }, 10000));
+  TEST_CHECK(counter.load() == TOTAL);
+}
+
+void
+test_tp_repeated_resize_stress()
+{
+  ThreadPool tp(2, 64, "test.resize");
+
+  const int ROUNDS = 30;
+  const int PER_ROUND = 20;
+  const int TOTAL = ROUNDS * PER_ROUND;
+  std::atomic<int> counter{0};
+
+  for(int r = 0; r < ROUNDS; ++r)
+    {
+      std::size_t target = 1 + (r % 5);
+      int rv = tp.set_threads(target);
+      TEST_CHECK(rv == 0);
+
+      for(int i = 0; i < PER_ROUND; ++i)
+        tp.enqueue_work([&counter](){ counter.fetch_add(1); });
+    }
+
+  TEST_CHECK(wait_until([&counter, TOTAL](){ return counter.load() == TOTAL; }, 10000));
+  TEST_CHECK(counter.load() == TOTAL);
+}
+
+void
+test_tp_many_producers_many_tasks_stress()
+{
+  ThreadPool tp(8, 256, "test.mpmt");
+
+  const int PRODUCERS = 8;
+  const int ITEMS_PER = 200;
+  const int TOTAL = PRODUCERS * ITEMS_PER;
+  std::atomic<int> counter{0};
+
+  std::vector<std::thread> producers;
+  for(int p = 0; p < PRODUCERS; ++p)
+    {
+      producers.emplace_back([&tp, &counter]()
+        {
+          auto ptok = tp.ptoken();
+          for(int i = 0; i < ITEMS_PER; ++i)
+            tp.enqueue_work(ptok, [&counter](){ counter.fetch_add(1); });
+        });
+    }
+
+  for(auto &t : producers)
+    t.join();
+
+  TEST_CHECK(wait_until([&counter, TOTAL](){ return counter.load() == TOTAL; }, 10000));
+  TEST_CHECK(counter.load() == TOTAL);
+}
+
+void
+test_tp_heavy_mixed_resize_and_enqueue_stress()
+{
+  ThreadPool tp(6, 512, "test.hmix");
+
+  const int PRODUCERS = 10;
+  const int PER_PRODUCER = 2500;
+  const int TOTAL = PRODUCERS * PER_PRODUCER;
+
+  std::atomic<int> executed{0};
+  std::atomic<bool> producers_done{false};
+  std::atomic<int> resize_ops{0};
+
+  std::thread resizer([&tp, &producers_done, &resize_ops]()
+    {
+      int i = 0;
+      while(!producers_done.load())
+        {
+          const std::size_t target = 2 + (i % 10);
+          int rv = tp.set_threads(target);
+          if(rv == 0)
+            resize_ops.fetch_add(1);
+          ++i;
+        }
+    });
+
+  std::vector<std::thread> producers;
+  producers.reserve(PRODUCERS);
+  for(int p = 0; p < PRODUCERS; ++p)
+    {
+      producers.emplace_back([&tp, &executed]()
+        {
+          auto ptok = tp.ptoken();
+
+          for(int i = 0; i < PER_PRODUCER; ++i)
+            tp.enqueue_work(ptok, [&executed](){ executed.fetch_add(1); });
+        });
+    }
+
+  for(auto &t : producers)
+    t.join();
+
+  producers_done.store(true);
+  resizer.join();
+
+  TEST_CHECK(resize_ops.load() > 0);
+  TEST_CHECK(wait_until([&executed, TOTAL](){ return executed.load() == TOTAL; }, 30000));
+  TEST_CHECK(executed.load() == TOTAL);
+}
+
+void
+test_tp_heavy_try_enqueue_pressure()
+{
+  ThreadPool tp(1, 1, "test.hpress");
+
+  const int PRODUCERS = 6;
+  const int ATTEMPTS_PER = 2500;
+
+  std::atomic<int> accepted{0};
+  std::atomic<int> rejected{0};
+  std::atomic<int> executed{0};
+
+  std::vector<std::thread> producers;
+  producers.reserve(PRODUCERS);
+  for(int p = 0; p < PRODUCERS; ++p)
+    {
+      producers.emplace_back([&tp, &accepted, &rejected, &executed]()
+        {
+          auto ptok = tp.ptoken();
+
+          for(int i = 0; i < ATTEMPTS_PER; ++i)
+            {
+              bool ok = tp.try_enqueue_work_for(ptok,
+                                                200,
+                                                [&executed]()
+                                                {
+                                                  std::this_thread::sleep_for(std::chrono::microseconds(50));
+                                                  executed.fetch_add(1);
+                                                });
+              if(ok)
+                accepted.fetch_add(1);
+              else
+                rejected.fetch_add(1);
+            }
+        });
+    }
+
+  for(auto &t : producers)
+    t.join();
+
+  TEST_CHECK(accepted.load() > 0);
+  TEST_CHECK(rejected.load() > 0);
+
+  TEST_CHECK(wait_until([&executed, &accepted]()
+                        {
+                          return executed.load() == accepted.load();
+                        },
+                        30000));
+  TEST_CHECK(executed.load() == accepted.load());
+}
+
+void
+test_tp_heavy_repeated_construct_destroy()
+{
+  const int ROUNDS = 150;
+
+  for(int r = 0; r < ROUNDS; ++r)
+    {
+      std::atomic<int> counter{0};
+
+      {
+        ThreadPool tp(4, 128, "test.hctor");
+
+        for(int i = 0; i < 400; ++i)
+          tp.enqueue_work([&counter]()
+            {
+              std::this_thread::sleep_for(std::chrono::microseconds(25));
+              counter.fetch_add(1);
+            });
+      }
+
+      TEST_CHECK(counter.load() == 400);
+    }
+}
+
+void
+test_tp_heavy_enqueue_task_mixed_outcomes()
+{
+  ThreadPool tp(8, 512, "test.htask");
+
+  const int N = 12000;
+
+  std::vector<std::future<int>> futures;
+  futures.reserve(N);
+
+  for(int i = 0; i < N; ++i)
+    {
+      futures.emplace_back(tp.enqueue_task([i]() -> int
+        {
+          if((i % 11) == 0)
+            throw std::runtime_error("heavy task error");
+
+          return i;
+        }));
+    }
+
+  long long expected_sum = 0;
+  int expected_success = 0;
+  int expected_errors = 0;
+
+  for(int i = 0; i < N; ++i)
+    {
+      if((i % 11) == 0)
+        {
+          expected_errors += 1;
+        }
+      else
+        {
+          expected_success += 1;
+          expected_sum += i;
+        }
+    }
+
+  int actual_success = 0;
+  int actual_errors = 0;
+  long long actual_sum = 0;
+
+  for(auto &f : futures)
+    {
+      try
+        {
+          actual_sum += f.get();
+          actual_success += 1;
+        }
+      catch(const std::runtime_error &e)
+        {
+          actual_errors += 1;
+          TEST_CHECK(std::string(e.what()) == "heavy task error");
+        }
+    }
+
+  TEST_CHECK(actual_success == expected_success);
+  TEST_CHECK(actual_errors == expected_errors);
+  TEST_CHECK(actual_sum == expected_sum);
+}
+
+void
+test_tp_heavy_add_remove_churn_under_enqueue()
+{
+  ThreadPool tp(6, 512, "test.hchurn");
+
+  const int PRODUCERS = 6;
+  const int PER_PRODUCER = 2200;
+  const int TOTAL = PRODUCERS * PER_PRODUCER;
+  const int CHURN_OPS = 700;
+
+  std::atomic<int> executed{0};
+  std::atomic<bool> producers_done{false};
+  std::atomic<int> add_ok{0};
+  std::atomic<int> remove_ok{0};
+
+  std::thread churner([&tp, &producers_done, &add_ok, &remove_ok]()
+    {
+      int i = 0;
+      while(!producers_done.load() && i < CHURN_OPS)
+        {
+          int rv_add = tp.add_thread();
+          if(rv_add == 0)
+            add_ok.fetch_add(1);
+
+          int rv_remove = tp.remove_thread();
+          if(rv_remove == 0)
+            remove_ok.fetch_add(1);
+
+          ++i;
+        }
+    });
+
+  std::vector<std::thread> producers;
+  producers.reserve(PRODUCERS);
+  for(int p = 0; p < PRODUCERS; ++p)
+    {
+      producers.emplace_back([&tp, &executed]()
+        {
+          auto ptok = tp.ptoken();
+          for(int i = 0; i < PER_PRODUCER; ++i)
+            tp.enqueue_work(ptok,
+                            [&executed]()
+                            {
+                              executed.fetch_add(1);
+                            });
+        });
+    }
+
+  for(auto &t : producers)
+    t.join();
+
+  producers_done.store(true);
+  churner.join();
+
+  TEST_CHECK(add_ok.load() > 0);
+  TEST_CHECK(remove_ok.load() > 0);
+  TEST_CHECK(wait_until([&executed, TOTAL](){ return executed.load() == TOTAL; }, 30000));
+  TEST_CHECK(executed.load() == TOTAL);
+}
+
 TEST_LIST =
   {
    {"nop",test_nop},
@@ -1047,5 +1570,18 @@ TEST_LIST =
    {"tp_destruction_drains_queue",test_tp_destruction_drains_queue},
    {"tp_move_only_callable",test_tp_move_only_callable},
    {"tp_work_ordering_single_thread",test_tp_work_ordering_single_thread},
+   {"tp_try_enqueue_work_fails_when_full",test_tp_try_enqueue_work_fails_when_full},
+   {"tp_try_enqueue_work_for_times_out_when_full",test_tp_try_enqueue_work_for_times_out_when_full},
+   {"tp_enqueue_work_blocks_until_slot_available",test_tp_enqueue_work_blocks_until_slot_available},
+   {"tp_worker_nonstd_exception_no_crash",test_tp_worker_nonstd_exception_no_crash},
+   {"tp_remove_thread_under_load",test_tp_remove_thread_under_load},
+   {"tp_set_threads_concurrent_with_enqueue",test_tp_set_threads_concurrent_with_enqueue},
+   {"tp_repeated_resize_stress",test_tp_repeated_resize_stress},
+   {"tp_many_producers_many_tasks_stress",test_tp_many_producers_many_tasks_stress},
+   {"tp_heavy_mixed_resize_and_enqueue_stress",test_tp_heavy_mixed_resize_and_enqueue_stress},
+   {"tp_heavy_try_enqueue_pressure",test_tp_heavy_try_enqueue_pressure},
+   {"tp_heavy_repeated_construct_destroy",test_tp_heavy_repeated_construct_destroy},
+   {"tp_heavy_enqueue_task_mixed_outcomes",test_tp_heavy_enqueue_task_mixed_outcomes},
+   {"tp_heavy_add_remove_churn_under_enqueue",test_tp_heavy_add_remove_churn_under_enqueue},
    {NULL,NULL}
   };
diff --git a/vendored/libfuse/include/thread_pool.hpp b/vendored/libfuse/include/thread_pool.hpp
index 5ceaa717..a37cf8ae 100644
--- a/vendored/libfuse/include/thread_pool.hpp
+++ b/vendored/libfuse/include/thread_pool.hpp
@@ -229,7 +229,7 @@ ThreadPool::start_routine(void *arg_)
         {
           done = true;
         }
-      catch(std::exception &e)
+      catch(const std::exception &e)
         {
           syslog(LOG_CRIT,
                  "threadpool (%s): uncaught exception caught by worker - %s",