Reverted commit D3755446

Summary:
Move ThreadLocal object destruction to occur under the lock to avoid races.
This causes a few cascading changes - the Tag lock needs to be a recursive_mutex so
constructing a new object while destroying another st. Also, forking requires
a new mutex to avoid deadlocking on accessing a recursive_mutex across a fork()

Reviewed By: andriigrynenko

Differential Revision: D3755446

fbshipit-source-id: f1f1f92175eb39e77aaa2add6915e5c9bb68d0fb

folly/ThreadCachedInt.h

@@ -63,11 +63,8 @@ class ThreadCachedInt : boost::noncopyable {
   // Reads the current value plus all the cached increments.  Requires grabbing
   // a lock, so this is significantly slower than readFast().
   IntT readFull() const {
-    // This could race with thread destruction and so the access lock should be
-    // acquired before reading the current value
-    auto accessor = cache_.accessAllThreads();
     IntT ret = readFast();
-    for (const auto& cache : accessor) {
+    for (const auto& cache : cache_.accessAllThreads()) {
       if (!cache.reset_.load(std::memory_order_acquire)) {
         ret += cache.val_.load(std::memory_order_relaxed);
       }
@@ -85,11 +82,8 @@ class ThreadCachedInt : boost::noncopyable {
   // little off, however, but it should be much better than calling readFull()
   // and set(0) sequentially.
   IntT readFullAndReset() {
-    // This could race with thread destruction and so the access lock should be
-    // acquired before reading the current value
-    auto accessor = cache_.accessAllThreads();
     IntT ret = readFastAndReset();
-    for (auto& cache : accessor) {
+    for (auto& cache : cache_.accessAllThreads()) {
       if (!cache.reset_.load(std::memory_order_acquire)) {
         ret += cache.val_.load(std::memory_order_relaxed);
         cache.reset_.store(true, std::memory_order_release);

folly/ThreadLocal.h

@@ -36,11 +36,10 @@
 
 #pragma once
 
-#include <boost/iterator/iterator_facade.hpp>
 #include <folly/Likely.h>
 #include <folly/Portability.h>
 #include <folly/ScopeGuard.h>
-#include <folly/SharedMutex.h>
+#include <boost/iterator/iterator_facade.hpp>
 #include <type_traits>
 #include <utility>
 
@@ -250,7 +249,6 @@ class ThreadLocalPtr {
     friend class ThreadLocalPtr<T,Tag>;
 
     threadlocal_detail::StaticMetaBase& meta_;
-    SharedMutex* accessAllThreadsLock_;
     std::mutex* lock_;
     uint32_t id_;
 
@@ -324,11 +322,9 @@ class ThreadLocalPtr {
 
     Accessor(Accessor&& other) noexcept
       : meta_(other.meta_),
-          accessAllThreadsLock_(other.accessAllThreadsLock_),
         lock_(other.lock_),
         id_(other.id_) {
       other.id_ = 0;
-      other.accessAllThreadsLock_ = nullptr;
       other.lock_ = nullptr;
     }
 
@@ -342,23 +338,20 @@ class ThreadLocalPtr {
       assert(&meta_ == &other.meta_);
       assert(lock_ == nullptr);
       using std::swap;
-      swap(accessAllThreadsLock_, other.accessAllThreadsLock_);
       swap(lock_, other.lock_);
       swap(id_, other.id_);
     }
 
     Accessor()
       : meta_(threadlocal_detail::StaticMeta<Tag>::instance()),
-          accessAllThreadsLock_(nullptr),
         lock_(nullptr),
-          id_(0) {}
+        id_(0) {
+    }
 
    private:
     explicit Accessor(uint32_t id)
       : meta_(threadlocal_detail::StaticMeta<Tag>::instance()),
-          accessAllThreadsLock_(&meta_.accessAllThreadsLock_),
         lock_(&meta_.lock_) {
-      accessAllThreadsLock_->lock();
       lock_->lock();
       id_ = id;
     }
@@ -366,11 +359,8 @@ class ThreadLocalPtr {
     void release() {
       if (lock_) {
         lock_->unlock();
-        DCHECK(accessAllThreadsLock_ != nullptr);
-        accessAllThreadsLock_->unlock();
         id_ = 0;
         lock_ = nullptr;
-        accessAllThreadsLock_ = nullptr;
       }
     }
   };

folly/detail/ThreadLocalDetail.cpp

@@ -44,8 +44,6 @@ void StaticMetaBase::onThreadExit(void* ptr) {
     pthread_setspecific(meta.pthreadKey_, nullptr);
   };
 
-  {
-    SharedMutex::ReadHolder rlock(meta.accessAllThreadsLock_);
   {
     std::lock_guard<std::mutex> g(meta.lock_);
     meta.erase(&(*threadEntry));
@@ -64,7 +62,6 @@ void StaticMetaBase::onThreadExit(void* ptr) {
       }
     }
   }
-  }
   free(threadEntry->elements);
   threadEntry->elements = nullptr;
   threadEntry->meta = nullptr;

folly/detail/ThreadLocalDetail.h

@@ -296,7 +296,6 @@ struct StaticMetaBase {
   uint32_t nextId_;
   std::vector<uint32_t> freeIds_;
   std::mutex lock_;
-  SharedMutex accessAllThreadsLock_;
   pthread_key_t pthreadKey_;
   ThreadEntry head_;
   ThreadEntry* (*threadEntry_)();

folly/test/ThreadCachedIntTest.cpp

@@ -17,7 +17,6 @@
 #include <folly/ThreadCachedInt.h>
 
 #include <atomic>
-#include <condition_variable>
 #include <thread>
 
 #include <glog/logging.h>
@@ -29,139 +28,6 @@
 
 using namespace folly;
 
-using std::unique_ptr;
-using std::vector;
-
-using Counter = ThreadCachedInt<int64_t>;
-
-class ThreadCachedIntTest : public testing::Test {
- public:
-  uint32_t GetDeadThreadsTotal(const Counter& counter) {
-    return counter.readFast();
-  }
-};
-
-// Multithreaded tests.  Creates a specified number of threads each of
-// which iterates a different amount and dies.
-
-namespace {
-// Set cacheSize to be large so cached data moves to target_ only when
-// thread dies.
-Counter g_counter_for_mt_slow(0, UINT32_MAX);
-Counter g_counter_for_mt_fast(0, UINT32_MAX);
-
-// Used to sync between threads.  The value of this variable is the
-// maximum iteration index upto which Runner() is allowed to go.
-uint32_t g_sync_for_mt(0);
-std::condition_variable cv;
-std::mutex cv_m;
-
-// Performs the specified number of iterations.  Within each
-// iteration, it increments counter 10 times.  At the beginning of
-// each iteration it checks g_sync_for_mt to see if it can proceed,
-// otherwise goes into a loop sleeping and rechecking.
-void Runner(Counter* counter, uint32_t iterations) {
-  for (uint32_t i = 0; i < iterations; ++i) {
-    std::unique_lock<std::mutex> lk(cv_m);
-    cv.wait(lk, [i] { return i < g_sync_for_mt; });
-    for (uint32_t j = 0; j < 10; ++j) {
-      counter->increment(1);
-    }
-  }
-}
-}
-
-// Slow test with fewer threads where there are more busy waits and
-// many calls to readFull().  This attempts to test as many of the
-// code paths in Counter as possible to ensure that counter values are
-// properly passed from thread local state, both at calls to
-// readFull() and at thread death.
-TEST_F(ThreadCachedIntTest, MultithreadedSlow) {
-  static constexpr uint32_t kNumThreads = 20;
-  g_sync_for_mt = 0;
-  vector<unique_ptr<std::thread>> threads(kNumThreads);
-  // Creates kNumThreads threads.  Each thread performs a different
-  // number of iterations in Runner() - threads[0] performs 1
-  // iteration, threads[1] performs 2 iterations, threads[2] performs
-  // 3 iterations, and so on.
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    threads[i].reset(new std::thread(Runner, &g_counter_for_mt_slow, i + 1));
-  }
-  // Variable to grab current counter value.
-  int32_t counter_value;
-  // The expected value of the counter.
-  int32_t total = 0;
-  // The expected value of GetDeadThreadsTotal().
-  int32_t dead_total = 0;
-  // Each iteration of the following thread allows one additional
-  // iteration of the threads.  Given that the threads perform
-  // different number of iterations from 1 through kNumThreads, one
-  // thread will complete in each of the iterations of the loop below.
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    // Allow upto iteration i on all threads.
-    {
-      std::lock_guard<std::mutex> lk(cv_m);
-      g_sync_for_mt = i + 1;
-    }
-    cv.notify_all();
-    total += (kNumThreads - i) * 10;
-    // Loop until the counter reaches its expected value.
-    do {
-      counter_value = g_counter_for_mt_slow.readFull();
-    } while (counter_value < total);
-    // All threads have done what they can until iteration i, now make
-    // sure they don't go further by checking 10 more times in the
-    // following loop.
-    for (uint32_t j = 0; j < 10; ++j) {
-      counter_value = g_counter_for_mt_slow.readFull();
-      EXPECT_EQ(total, counter_value);
-    }
-    dead_total += (i + 1) * 10;
-    EXPECT_GE(dead_total, GetDeadThreadsTotal(g_counter_for_mt_slow));
-  }
-  // All threads are done.
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    threads[i]->join();
-  }
-  counter_value = g_counter_for_mt_slow.readFull();
-  EXPECT_EQ(total, counter_value);
-  EXPECT_EQ(total, dead_total);
-  EXPECT_EQ(dead_total, GetDeadThreadsTotal(g_counter_for_mt_slow));
-}
-
-// Fast test with lots of threads and only one call to readFull()
-// at the end.
-TEST_F(ThreadCachedIntTest, MultithreadedFast) {
-  static constexpr uint32_t kNumThreads = 1000;
-  g_sync_for_mt = 0;
-  vector<unique_ptr<std::thread>> threads(kNumThreads);
-  // Creates kNumThreads threads.  Each thread performs a different
-  // number of iterations in Runner() - threads[0] performs 1
-  // iteration, threads[1] performs 2 iterations, threads[2] performs
-  // 3 iterations, and so on.
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    threads[i].reset(new std::thread(Runner, &g_counter_for_mt_fast, i + 1));
-  }
-  // Let the threads run to completion.
-  {
-    std::lock_guard<std::mutex> lk(cv_m);
-    g_sync_for_mt = kNumThreads;
-  }
-  cv.notify_all();
-  // The expected value of the counter.
-  uint32_t total = 0;
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    total += (kNumThreads - i) * 10;
-  }
-  // Wait for all threads to complete.
-  for (uint32_t i = 0; i < kNumThreads; ++i) {
-    threads[i]->join();
-  }
-  int32_t counter_value = g_counter_for_mt_fast.readFull();
-  EXPECT_EQ(total, counter_value);
-  EXPECT_EQ(total, GetDeadThreadsTotal(g_counter_for_mt_fast));
-}
-
 TEST(ThreadCachedInt, SingleThreadedNotCached) {
   ThreadCachedInt<int64_t> val(0, 0);
   EXPECT_EQ(0, val.readFast());