Revert "Stop using std::thread in C++ library since it can trigger exceptions"

10 files changed, 60 insertions, 180 deletions

diff --git a/src/cpp/client/secure_credentials.cc b/src/cpp/client/secure_credentials.cc
index 94519d817b..4fb128d98b 100644
--- a/src/cpp/client/secure_credentials.cc
+++ b/src/cpp/client/secure_credentials.cc
@@ -189,16 +189,10 @@ int MetadataCredentialsPluginWrapper::GetMetadata(
   }
   if (w->plugin_->IsBlocking()) {
     // Asynchronous return.
-    if (w->thread_pool_->Add(std::bind(
-            &MetadataCredentialsPluginWrapper::InvokePlugin, w, context, cb,
-            user_data, nullptr, nullptr, nullptr, nullptr))) {
-      return 0;
-    } else {
-      *num_creds_md = 0;
-      *status = GRPC_STATUS_RESOURCE_EXHAUSTED;
-      *error_details = nullptr;
-      return true;
-    }
+    w->thread_pool_->Add(
+        std::bind(&MetadataCredentialsPluginWrapper::InvokePlugin, w, context,
+                  cb, user_data, nullptr, nullptr, nullptr, nullptr));
+    return 0;
   } else {
     // Synchronous return.
     w->InvokePlugin(context, cb, user_data, creds_md, num_creds_md, status,
diff --git a/src/cpp/server/create_default_thread_pool.cc b/src/cpp/server/create_default_thread_pool.cc
index 2d2abbe9d1..8ca3e32c2f 100644
--- a/src/cpp/server/create_default_thread_pool.cc
+++ b/src/cpp/server/create_default_thread_pool.cc
@@ -28,7 +28,7 @@ namespace {
 ThreadPoolInterface* CreateDefaultThreadPoolImpl() {
   int cores = gpr_cpu_num_cores();
   if (!cores) cores = 4;
-  return new DynamicThreadPool(cores, gpr_thd_new, gpr_thd_join);
+  return new DynamicThreadPool(cores);
 }
 
 CreateThreadPoolFunc g_ctp_impl = CreateDefaultThreadPoolImpl;
diff --git a/src/cpp/server/dynamic_thread_pool.cc b/src/cpp/server/dynamic_thread_pool.cc
index d0e62313f6..81c78fe739 100644
--- a/src/cpp/server/dynamic_thread_pool.cc
+++ b/src/cpp/server/dynamic_thread_pool.cc
@@ -19,32 +19,19 @@
 #include "src/cpp/server/dynamic_thread_pool.h"
 
 #include <mutex>
+#include <thread>
 
 #include <grpc/support/log.h>
-#include <grpc/support/thd.h>
 
 namespace grpc {
 
-DynamicThreadPool::DynamicThread::DynamicThread(DynamicThreadPool* pool,
-                                                bool* valid)
-    : pool_(pool) {
-  gpr_thd_options opt = gpr_thd_options_default();
-  gpr_thd_options_set_joinable(&opt);
-
-  std::lock_guard<std::mutex> l(dt_mu_);
-  valid_ = *valid = pool->thread_creator_(
-      &thd_, "dynamic thread",
-      [](void* th) {
-        reinterpret_cast<DynamicThreadPool::DynamicThread*>(th)->ThreadFunc();
-      },
-      this, &opt);
-}
-
+DynamicThreadPool::DynamicThread::DynamicThread(DynamicThreadPool* pool)
+    : pool_(pool),
+      thd_(new std::thread(&DynamicThreadPool::DynamicThread::ThreadFunc,
+                           this)) {}
 DynamicThreadPool::DynamicThread::~DynamicThread() {
-  std::lock_guard<std::mutex> l(dt_mu_);
-  if (valid_) {
-    pool_->thread_joiner_(thd_);
-  }
+  thd_->join();
+  thd_.reset();
 }
 
 void DynamicThreadPool::DynamicThread::ThreadFunc() {
@@ -86,26 +73,15 @@ void DynamicThreadPool::ThreadFunc() {
   }
 }
 
-DynamicThreadPool::DynamicThreadPool(
-    int reserve_threads,
-    std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                      const gpr_thd_options*)>
-        thread_creator,
-    std::function<void(gpr_thd_id)> thread_joiner)
+DynamicThreadPool::DynamicThreadPool(int reserve_threads)
     : shutdown_(false),
       reserve_threads_(reserve_threads),
       nthreads_(0),
-      threads_waiting_(0),
-      thread_creator_(thread_creator),
-      thread_joiner_(thread_joiner) {
+      threads_waiting_(0) {
   for (int i = 0; i < reserve_threads_; i++) {
     std::lock_guard<std::mutex> lock(mu_);
     nthreads_++;
-    bool valid;
-    auto* th = new DynamicThread(this, &valid);
-    if (!valid) {
-      delete th;
-    }
+    new DynamicThread(this);
   }
 }
 
@@ -125,7 +101,7 @@ DynamicThreadPool::~DynamicThreadPool() {
   ReapThreads(&dead_threads_);
 }
 
-bool DynamicThreadPool::Add(const std::function<void()>& callback) {
+void DynamicThreadPool::Add(const std::function<void()>& callback) {
   std::lock_guard<std::mutex> lock(mu_);
   // Add works to the callbacks list
   callbacks_.push(callback);
@@ -133,12 +109,7 @@ bool DynamicThreadPool::Add(const std::function<void()>& callback) {
   if (threads_waiting_ == 0) {
     // Kick off a new thread
     nthreads_++;
-    bool valid;
-    auto* th = new DynamicThread(this, &valid);
-    if (!valid) {
-      delete th;
-      return false;
-    }
+    new DynamicThread(this);
   } else {
     cv_.notify_one();
   }
@@ -146,7 +117,6 @@ bool DynamicThreadPool::Add(const std::function<void()>& callback) {
   if (!dead_threads_.empty()) {
     ReapThreads(&dead_threads_);
   }
-  return true;
 }
 
 }  // namespace grpc
diff --git a/src/cpp/server/dynamic_thread_pool.h b/src/cpp/server/dynamic_thread_pool.h
index 75d31cd908..9237c6e5ca 100644
--- a/src/cpp/server/dynamic_thread_pool.h
+++ b/src/cpp/server/dynamic_thread_pool.h
@@ -24,9 +24,9 @@
 #include <memory>
 #include <mutex>
 #include <queue>
+#include <thread>
 
 #include <grpc++/support/config.h>
-#include <grpc/support/thd.h>
 
 #include "src/cpp/server/thread_pool_interface.h"
 
@@ -34,26 +34,20 @@ namespace grpc {
 
 class DynamicThreadPool final : public ThreadPoolInterface {
  public:
-  DynamicThreadPool(int reserve_threads,
-                    std::function<int(gpr_thd_id*, const char*, void (*)(void*),
-                                      void*, const gpr_thd_options*)>
-                        thread_creator,
-                    std::function<void(gpr_thd_id)> thread_joiner);
+  explicit DynamicThreadPool(int reserve_threads);
   ~DynamicThreadPool();
 
-  bool Add(const std::function<void()>& callback) override;
+  void Add(const std::function<void()>& callback) override;
 
  private:
   class DynamicThread {
    public:
-    DynamicThread(DynamicThreadPool* pool, bool* valid);
+    DynamicThread(DynamicThreadPool* pool);
     ~DynamicThread();
 
    private:
     DynamicThreadPool* pool_;
-    std::mutex dt_mu_;
-    gpr_thd_id thd_;
-    bool valid_;
+    std::unique_ptr<std::thread> thd_;
     void ThreadFunc();
   };
   std::mutex mu_;
@@ -65,10 +59,6 @@ class DynamicThreadPool final : public ThreadPoolInterface {
   int nthreads_;
   int threads_waiting_;
   std::list<DynamicThread*> dead_threads_;
-  std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                    const gpr_thd_options*)>
-      thread_creator_;
-  std::function<void(gpr_thd_id)> thread_joiner_;
 
   void ThreadFunc();
   static void ReapThreads(std::list<DynamicThread*>* tlist);
diff --git a/src/cpp/server/secure_server_credentials.cc b/src/cpp/server/secure_server_credentials.cc
index fa08a6200f..0fbe4ccd18 100644
--- a/src/cpp/server/secure_server_credentials.cc
+++ b/src/cpp/server/secure_server_credentials.cc
@@ -43,14 +43,9 @@ void AuthMetadataProcessorAyncWrapper::Process(
     return;
   }
   if (w->processor_->IsBlocking()) {
-    bool added = w->thread_pool_->Add(
+    w->thread_pool_->Add(
         std::bind(&AuthMetadataProcessorAyncWrapper::InvokeProcessor, w,
                   context, md, num_md, cb, user_data));
-    if (!added) {
-      // no thread available, so fail with temporary resource unavailability
-      cb(user_data, nullptr, 0, nullptr, 0, GRPC_STATUS_UNAVAILABLE, nullptr);
-      return;
-    }
   } else {
     // invoke directly.
     w->InvokeProcessor(context, md, num_md, cb, user_data);
diff --git a/src/cpp/server/server_builder.cc b/src/cpp/server/server_builder.cc
index d91ee7f4e3..200e477822 100644
--- a/src/cpp/server/server_builder.cc
+++ b/src/cpp/server/server_builder.cc
@@ -23,7 +23,6 @@
 #include <grpc++/server.h>
 #include <grpc/support/cpu.h>
 #include <grpc/support/log.h>
-#include <grpc/support/thd.h>
 #include <grpc/support/useful.h>
 
 #include "src/cpp/server/thread_pool_interface.h"
@@ -44,9 +43,7 @@ ServerBuilder::ServerBuilder()
       max_send_message_size_(-1),
       sync_server_settings_(SyncServerSettings()),
       resource_quota_(nullptr),
-      generic_service_(nullptr),
-      thread_creator_(gpr_thd_new),
-      thread_joiner_(gpr_thd_join) {
+      generic_service_(nullptr) {
   gpr_once_init(&once_init_plugin_list, do_plugin_list_init);
   for (auto it = g_plugin_factory_list->begin();
        it != g_plugin_factory_list->end(); it++) {
@@ -265,7 +262,7 @@ std::unique_ptr<Server> ServerBuilder::BuildAndStart() {
   std::unique_ptr<Server> server(new Server(
       max_receive_message_size_, &args, sync_server_cqs,
       sync_server_settings_.min_pollers, sync_server_settings_.max_pollers,
-      sync_server_settings_.cq_timeout_msec, thread_creator_, thread_joiner_));
+      sync_server_settings_.cq_timeout_msec));
 
   if (has_sync_methods) {
     // This is a Sync server
diff --git a/src/cpp/server/server_cc.cc b/src/cpp/server/server_cc.cc
index 02a663d660..4f8f4e06fc 100644
--- a/src/cpp/server/server_cc.cc
+++ b/src/cpp/server/server_cc.cc
@@ -36,7 +36,6 @@
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
-#include <grpc/support/thd.h>
 
 #include "src/core/ext/transport/inproc/inproc_transport.h"
 #include "src/core/lib/profiling/timers.h"
@@ -196,10 +195,8 @@ class Server::SyncRequest final : public internal::CompletionQueueTag {
           call_(mrd->call_, server, &cq_, server->max_receive_message_size()),
           ctx_(mrd->deadline_, &mrd->request_metadata_),
           has_request_payload_(mrd->has_request_payload_),
-          request_payload_(has_request_payload_ ? mrd->request_payload_
-                                                : nullptr),
-          method_(mrd->method_),
-          server_(server) {
+          request_payload_(mrd->request_payload_),
+          method_(mrd->method_) {
       ctx_.set_call(mrd->call_);
       ctx_.cq_ = &cq_;
       GPR_ASSERT(mrd->in_flight_);
@@ -213,13 +210,10 @@ class Server::SyncRequest final : public internal::CompletionQueueTag {
       }
     }
 
-    void Run(std::shared_ptr<GlobalCallbacks> global_callbacks,
-             bool resources) {
+    void Run(std::shared_ptr<GlobalCallbacks> global_callbacks) {
       ctx_.BeginCompletionOp(&call_);
       global_callbacks->PreSynchronousRequest(&ctx_);
-      auto* handler = resources ? method_->handler()
-                                : server_->resource_exhausted_handler_.get();
-      handler->RunHandler(internal::MethodHandler::HandlerParameter(
+      method_->handler()->RunHandler(internal::MethodHandler::HandlerParameter(
           &call_, &ctx_, request_payload_));
       global_callbacks->PostSynchronousRequest(&ctx_);
       request_payload_ = nullptr;
@@ -241,7 +235,6 @@ class Server::SyncRequest final : public internal::CompletionQueueTag {
     const bool has_request_payload_;
     grpc_byte_buffer* request_payload_;
     internal::RpcServiceMethod* const method_;
-    Server* server_;
   };
 
  private:
@@ -262,15 +255,11 @@ class Server::SyncRequest final : public internal::CompletionQueueTag {
 // appropriate RPC handlers
 class Server::SyncRequestThreadManager : public ThreadManager {
  public:
-  SyncRequestThreadManager(
-      Server* server, CompletionQueue* server_cq,
-      std::shared_ptr<GlobalCallbacks> global_callbacks, int min_pollers,
-      int max_pollers, int cq_timeout_msec,
-      std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                        const gpr_thd_options*)>
-          thread_creator,
-      std::function<void(gpr_thd_id)> thread_joiner)
-      : ThreadManager(min_pollers, max_pollers, thread_creator, thread_joiner),
+  SyncRequestThreadManager(Server* server, CompletionQueue* server_cq,
+                           std::shared_ptr<GlobalCallbacks> global_callbacks,
+                           int min_pollers, int max_pollers,
+                           int cq_timeout_msec)
+      : ThreadManager(min_pollers, max_pollers),
         server_(server),
         server_cq_(server_cq),
         cq_timeout_msec_(cq_timeout_msec),
@@ -296,7 +285,7 @@ class Server::SyncRequestThreadManager : public ThreadManager {
     GPR_UNREACHABLE_CODE(return TIMEOUT);
   }
 
-  void DoWork(void* tag, bool ok, bool resources) override {
+  void DoWork(void* tag, bool ok) override {
     SyncRequest* sync_req = static_cast<SyncRequest*>(tag);
 
     if (!sync_req) {
@@ -316,7 +305,7 @@ class Server::SyncRequestThreadManager : public ThreadManager {
       }
 
       GPR_TIMER_SCOPE("cd.Run()", 0);
-      cd.Run(global_callbacks_, resources);
+      cd.Run(global_callbacks_);
     }
     // TODO (sreek) If ok is false here (which it isn't in case of
     // grpc_request_registered_call), we should still re-queue the request
@@ -378,11 +367,7 @@ Server::Server(
     int max_receive_message_size, ChannelArguments* args,
     std::shared_ptr<std::vector<std::unique_ptr<ServerCompletionQueue>>>
         sync_server_cqs,
-    int min_pollers, int max_pollers, int sync_cq_timeout_msec,
-    std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                      const gpr_thd_options*)>
-        thread_creator,
-    std::function<void(gpr_thd_id)> thread_joiner)
+    int min_pollers, int max_pollers, int sync_cq_timeout_msec)
     : max_receive_message_size_(max_receive_message_size),
       sync_server_cqs_(sync_server_cqs),
       started_(false),
@@ -391,9 +376,7 @@ Server::Server(
       has_generic_service_(false),
       server_(nullptr),
       server_initializer_(new ServerInitializer(this)),
-      health_check_service_disabled_(false),
-      thread_creator_(thread_creator),
-      thread_joiner_(thread_joiner) {
+      health_check_service_disabled_(false) {
   g_gli_initializer.summon();
   gpr_once_init(&g_once_init_callbacks, InitGlobalCallbacks);
   global_callbacks_ = g_callbacks;
@@ -403,7 +386,7 @@ Server::Server(
        it++) {
     sync_req_mgrs_.emplace_back(new SyncRequestThreadManager(
         this, (*it).get(), global_callbacks_, min_pollers, max_pollers,
-        sync_cq_timeout_msec, thread_creator_, thread_joiner_));
+        sync_cq_timeout_msec));
   }
 
   grpc_channel_args channel_args;
@@ -566,10 +549,6 @@ void Server::Start(ServerCompletionQueue** cqs, size_t num_cqs) {
     }
   }
 
-  if (!sync_server_cqs_->empty()) {
-    resource_exhausted_handler_.reset(new internal::ResourceExhaustedHandler);
-  }
-
   for (auto it = sync_req_mgrs_.begin(); it != sync_req_mgrs_.end(); it++) {
     (*it)->Start();
   }
diff --git a/src/cpp/server/thread_pool_interface.h b/src/cpp/server/thread_pool_interface.h
index 656e6673f1..028842a776 100644
--- a/src/cpp/server/thread_pool_interface.h
+++ b/src/cpp/server/thread_pool_interface.h
@@ -29,9 +29,7 @@ class ThreadPoolInterface {
   virtual ~ThreadPoolInterface() {}
 
   // Schedule the given callback for execution.
-  // Return true on success, false on failure
-  virtual bool Add(const std::function<void()>& callback)
-      GRPC_MUST_USE_RESULT = 0;
+  virtual void Add(const std::function<void()>& callback) = 0;
 };
 
 // Allows different codebases to use their own thread pool impls
diff --git a/src/cpp/thread_manager/thread_manager.cc b/src/cpp/thread_manager/thread_manager.cc
index 107c60f4eb..23264f1b5b 100644
--- a/src/cpp/thread_manager/thread_manager.cc
+++ b/src/cpp/thread_manager/thread_manager.cc
@@ -20,26 +20,18 @@
 
 #include <climits>
 #include <mutex>
+#include <thread>
 
 #include <grpc/support/log.h>
-#include <grpc/support/thd.h>
 
 namespace grpc {
 
-ThreadManager::WorkerThread::WorkerThread(ThreadManager* thd_mgr, bool* valid)
+ThreadManager::WorkerThread::WorkerThread(ThreadManager* thd_mgr)
     : thd_mgr_(thd_mgr) {
-  gpr_thd_options opt = gpr_thd_options_default();
-  gpr_thd_options_set_joinable(&opt);
-
   // Make thread creation exclusive with respect to its join happening in
   // ~WorkerThread().
   std::lock_guard<std::mutex> lock(wt_mu_);
-  *valid = valid_ = thd_mgr->thread_creator_(
-      &thd_, "worker thread",
-      [](void* th) {
-        reinterpret_cast<ThreadManager::WorkerThread*>(th)->Run();
-      },
-      this, &opt);
+  thd_ = std::thread(&ThreadManager::WorkerThread::Run, this);
 }
 
 void ThreadManager::WorkerThread::Run() {
@@ -50,24 +42,15 @@ void ThreadManager::WorkerThread::Run() {
 ThreadManager::WorkerThread::~WorkerThread() {
   // Don't join until the thread is fully constructed.
   std::lock_guard<std::mutex> lock(wt_mu_);
-  if (valid_) {
-    thd_mgr_->thread_joiner_(thd_);
-  }
+  thd_.join();
 }
 
-ThreadManager::ThreadManager(
-    int min_pollers, int max_pollers,
-    std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                      const gpr_thd_options*)>
-        thread_creator,
-    std::function<void(gpr_thd_id)> thread_joiner)
+ThreadManager::ThreadManager(int min_pollers, int max_pollers)
     : shutdown_(false),
       num_pollers_(0),
       min_pollers_(min_pollers),
       max_pollers_(max_pollers == -1 ? INT_MAX : max_pollers),
-      num_threads_(0),
-      thread_creator_(thread_creator),
-      thread_joiner_(thread_joiner) {}
+      num_threads_(0) {}
 
 ThreadManager::~ThreadManager() {
   {
@@ -128,9 +111,7 @@ void ThreadManager::Initialize() {
 
   for (int i = 0; i < min_pollers_; i++) {
     // Create a new thread (which ends up calling the MainWorkLoop() function
-    bool valid;
-    new WorkerThread(this, &valid);
-    GPR_ASSERT(valid);  // we need to have at least this minimum
+    new WorkerThread(this);
   }
 }
 
@@ -157,27 +138,18 @@ void ThreadManager::MainWorkLoop() {
       case WORK_FOUND:
         // If we got work and there are now insufficient pollers, start a new
         // one
-        bool resources;
         if (!shutdown_ && num_pollers_ < min_pollers_) {
-          bool valid;
+          num_pollers_++;
+          num_threads_++;
           // Drop lock before spawning thread to avoid contention
           lock.unlock();
-          auto* th = new WorkerThread(this, &valid);
-          lock.lock();
-          if (valid) {
-            num_pollers_++;
-            num_threads_++;
-          } else {
-            delete th;
-          }
-          resources = (num_pollers_ > 0);
+          new WorkerThread(this);
         } else {
-          resources = true;
+          // Drop lock for consistency with above branch
+          lock.unlock();
         }
-        // Drop lock before any application work
-        lock.unlock();
         // Lock is always released at this point - do the application work
-        DoWork(tag, ok, resources);
+        DoWork(tag, ok);
         // Take the lock again to check post conditions
         lock.lock();
         // If we're shutdown, we should finish at this point.
diff --git a/src/cpp/thread_manager/thread_manager.h b/src/cpp/thread_manager/thread_manager.h
index c1783baa60..a206e0bd8a 100644
--- a/src/cpp/thread_manager/thread_manager.h
+++ b/src/cpp/thread_manager/thread_manager.h
@@ -20,23 +20,18 @@
 #define GRPC_INTERNAL_CPP_THREAD_MANAGER_H
 
 #include <condition_variable>
-#include <functional>
 #include <list>
 #include <memory>
 #include <mutex>
+#include <thread>
 
 #include <grpc++/support/config.h>
-#include <grpc/support/thd.h>
 
 namespace grpc {
 
 class ThreadManager {
  public:
-  ThreadManager(int min_pollers, int max_pollers,
-                std::function<int(gpr_thd_id*, const char*, void (*)(void*),
-                                  void*, const gpr_thd_options*)>
-                    thread_creator,
-                std::function<void(gpr_thd_id)> thread_joiner);
+  explicit ThreadManager(int min_pollers, int max_pollers);
   virtual ~ThreadManager();
 
   // Initializes and Starts the Rpc Manager threads
@@ -55,8 +50,6 @@ class ThreadManager {
   //  - ThreadManager does not interpret the values of 'tag' and 'ok'
   //  - ThreadManager WILL call DoWork() and pass '*tag' and 'ok' as input to
   //    DoWork()
-  //  - ThreadManager will also pass DoWork a bool saying if there are actually
-  //    resources to do the work
   //
   // If the return value is SHUTDOWN:,
   //  - ThreadManager WILL NOT call DoWork() and terminates the thead
@@ -76,7 +69,7 @@ class ThreadManager {
   // The implementation of DoWork() should also do any setup needed to ensure
   // that the next call to PollForWork() (not necessarily by the current thread)
   // actually finds some work
-  virtual void DoWork(void* tag, bool ok, bool resources) = 0;
+  virtual void DoWork(void* tag, bool ok) = 0;
 
   // Mark the ThreadManager as shutdown and begin draining the work. This is a
   // non-blocking call and the caller should call Wait(), a blocking call which
@@ -91,15 +84,15 @@ class ThreadManager {
   virtual void Wait();
 
  private:
-  // Helper wrapper class around thread. This takes a ThreadManager object
-  // and starts a new thread to calls the Run() function.
+  // Helper wrapper class around std::thread. This takes a ThreadManager object
+  // and starts a new std::thread to calls the Run() function.
   //
   // The Run() function calls ThreadManager::MainWorkLoop() function and once
   // that completes, it marks the WorkerThread completed by calling
   // ThreadManager::MarkAsCompleted()
   class WorkerThread {
    public:
-    WorkerThread(ThreadManager* thd_mgr, bool* valid);
+    WorkerThread(ThreadManager* thd_mgr);
     ~WorkerThread();
 
    private:
@@ -109,8 +102,7 @@ class ThreadManager {
 
     ThreadManager* const thd_mgr_;
     std::mutex wt_mu_;
-    gpr_thd_id thd_;
-    bool valid_;
+    std::thread thd_;
   };
 
   // The main funtion in ThreadManager
@@ -137,13 +129,6 @@ class ThreadManager {
   // currently polling i.e num_pollers_)
   int num_threads_;
 
-  // Functions for creating/joining threads. Normally, these should
-  // be gpr_thd_new/gpr_thd_join but they are overridable
-  std::function<int(gpr_thd_id*, const char*, void (*)(void*), void*,
-                    const gpr_thd_options*)>
-      thread_creator_;
-  std::function<void(gpr_thd_id)> thread_joiner_;
-
   std::mutex list_mu_;
   std::list<WorkerThread*> completed_threads_;
 };