Merge pull request #2446

6d0ca7d1 Tweak concurrency limits (Howard Chu)
510d0d47 Use a threadpool (Howard Chu)

8 files changed, 207 insertions, 619 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 55b8ad3e6..19d90253b 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -37,8 +37,7 @@ set(common_sources
   i18n.cpp
   password.cpp
   perf_timer.cpp
-  task_region.cpp
-  thread_group.cpp
+  threadpool.cpp
   updates.cpp)
 
 if (STACK_TRACE)
@@ -66,8 +65,7 @@ set(common_private_headers
   password.h
   perf_timer.h
   stack_trace.h
-  task_region.h
-  thread_group.h
+  threadpool.h
   updates.h)
 
 monero_private_headers(common
diff --git a/src/common/common_fwd.h b/src/common/common_fwd.h
index 5d67251b1..f33e185b5 100644
--- a/src/common/common_fwd.h
+++ b/src/common/common_fwd.h
@@ -36,6 +36,5 @@ namespace tools
   struct login;
   class password_container;
   class t_http_connection;
-  class task_region;
-  class thread_group;
+  class threadpool;
 }
diff --git a/src/common/task_region.cpp b/src/common/task_region.cpp
deleted file mode 100644
index 9b4620c6e..000000000
--- a/src/common/task_region.cpp
+++ /dev/null
@@ -1,94 +0,0 @@
-// Copyright (c) 2014-2017, The Monero Project
-// 
-// All rights reserved.
-// 
-// Redistribution and use in source and binary forms, with or without modification, are
-// permitted provided that the following conditions are met:
-// 
-// 1. Redistributions of source code must retain the above copyright notice, this list of
-//    conditions and the following disclaimer.
-// 
-// 2. Redistributions in binary form must reproduce the above copyright notice, this list
-//    of conditions and the following disclaimer in the documentation and/or other
-//    materials provided with the distribution.
-// 
-// 3. Neither the name of the copyright holder nor the names of its contributors may be
-//    used to endorse or promote products derived from this software without specific
-//    prior written permission.
-// 
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
-// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
-// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
-// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
-// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
-// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#include "common/task_region.h"
-
-#include <boost/thread/locks.hpp>
-#include <cassert>
-
-/* `mark_completed` and `wait` can throw in the lock call, but its difficult to
-recover from either. An exception in `wait` means the post condition of joining
-all threads cannot be achieved, and an exception in `mark_completed` means
-certain deadlock. `noexcept` qualifier will force a call to `std::terminate` if
-locking throws an exception, which should only happen if a recursive lock
-attempt is made (which is not possible since no external function is called
-while holding the lock). */
-
-namespace tools
-{
-void task_region_handle::state::mark_completed(id task_id) noexcept {
-  assert(task_id != 0 && (task_id & (task_id - 1)) == 0); // power of 2 check
-  if (pending.fetch_and(~task_id) == task_id) {
-    // synchronize with wait call, but do not need to hold
-    boost::unique_lock<boost::mutex>{sync_on_complete};
-    all_complete.notify_all();
-  }
-}
-
-void task_region_handle::state::abort() noexcept {
-  state* current = this;
-  while (current) {
-    current->ready = 0;
-    current = current->next.get();
-  }
-}
-
-void task_region_handle::state::wait() noexcept {
-  state* current = this;
-  while (current) {
-    {
-      boost::unique_lock<boost::mutex> lock{current->sync_on_complete};
-      current->all_complete.wait(lock, [current] { return current->pending == 0; });
-    }
-    current = current->next.get();
-  }
-}
-
-void task_region_handle::state::wait(thread_group& threads) noexcept {
-  state* current = this;
-  while (current) {
-    while (current->pending != 0) {
-      if (!threads.try_run_one()) {
-        current->wait();
-        return;
-      }
-    }
-    current = current->next.get();
-  }
-}
-
-void task_region_handle::create_state() {
-  st = std::make_shared<state>(std::move(st));
-  next_id = 1;
-}
-
-void task_region_handle::do_wait() noexcept {
-  assert(st);
-  const std::shared_ptr<state> temp = std::move(st);
-  temp->wait(threads);
-}
-}
diff --git a/src/common/task_region.h b/src/common/task_region.h
deleted file mode 100644
index 30972cce3..000000000
--- a/src/common/task_region.h
+++ /dev/null
@@ -1,223 +0,0 @@
-// Copyright (c) 2014-2017, The Monero Project
-// 
-// All rights reserved.
-// 
-// Redistribution and use in source and binary forms, with or without modification, are
-// permitted provided that the following conditions are met:
-// 
-// 1. Redistributions of source code must retain the above copyright notice, this list of
-//    conditions and the following disclaimer.
-// 
-// 2. Redistributions in binary form must reproduce the above copyright notice, this list
-//    of conditions and the following disclaimer in the documentation and/or other
-//    materials provided with the distribution.
-// 
-// 3. Neither the name of the copyright holder nor the names of its contributors may be
-//    used to endorse or promote products derived from this software without specific
-//    prior written permission.
-// 
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
-// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
-// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
-// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
-// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
-// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#pragma once
-
-#include <atomic>
-#include <boost/thread/condition_variable.hpp>
-#include <boost/thread/mutex.hpp>
-#include <memory>
-#include <type_traits>
-#include <utility>
-
-#include "common/thread_group.h"
-
-namespace tools
-{
-
-/*! A model of the fork-join concept. `run(...)` "forks" (i.e. spawns new
-tasks), and `~task_region_handle()` or `wait()` "joins" the spawned tasks.
-`wait` will block until all tasks have completed, while `~task_region_handle()`
-blocks until all tasks have completed or aborted.
-
-Do _NOT_ give this object to separate thread of execution (which includes
-`task_region_handle::run(...)`) because joining on a different thread is
-undesireable (potential deadlock). 
-
-This class cannot be constructed directly, use the function
-`task_region(...)` instead.
-*/
-class task_region_handle
-{
-  struct state
-  {
-    using id = unsigned;
-
-    explicit state(std::shared_ptr<state> next_src) noexcept
-      : next(std::move(next_src))
-      , ready(0)
-      , pending(0)
-      , sync_on_complete()
-      , all_complete() {
-    }
-      
-    state(const state&) = default;
-    state(state&&) = default;
-    ~state() = default;
-    state& operator=(const state&) = default;
-    state& operator=(state&&) = default;
-
-    void track_id(id task_id) noexcept {
-      pending |= task_id;
-      ready |= task_id;
-    }
-
-    //! \return True only once whether a given id can execute
-    bool can_run(id task_id) noexcept {
-      return (ready.fetch_and(~task_id) & task_id);
-    }
-
-    //! Mark id as completed, and synchronize with waiting threads
-    void mark_completed(id task_id) noexcept;
-
-    //! Tell all unstarted functions in region to return immediately
-    void abort() noexcept;
-
-    //! Blocks until all functions in region have aborted or completed.
-    void wait() noexcept;
-
-    //! Same as `wait()`, except `this_thread` runs tasks while waiting.
-    void wait(thread_group& threads) noexcept;
-
-  private:
-    /* This implementation is a bit pessimistic, it ensures that all copies
-    of a wrapped task can only be executed once. `thread_group` should never
-    do this, but some variable needs to track whether an abort should be done
-    anyway... */
-    std::shared_ptr<state> next;
-    std::atomic<id> ready;   //!< Tracks whether a task has been invoked
-    std::atomic<id> pending; //!< Tracks when a task has completed or aborted
-    boost::mutex sync_on_complete;
-    boost::condition_variable all_complete;
-  };
-
-  template<typename F>
-  struct wrapper
-  {
-    wrapper(state::id id_src, std::shared_ptr<state> st_src, F f_src)
-      : task_id(id_src), st(std::move(st_src)), f(std::move(f_src)) {
-    }
-
-    wrapper(const wrapper&) = default;
-    wrapper(wrapper&&) = default;
-    wrapper& operator=(const wrapper&) = default;
-    wrapper& operator=(wrapper&&) = default;
-
-    void operator()() {
-      if (st) {
-        if (st->can_run(task_id)) {
-          f();
-        }
-        st->mark_completed(task_id);
-      }
-    }
-
-  private:
-    const state::id task_id;
-    std::shared_ptr<state> st;
-    F f;
-  };
-
-public:
-  friend struct task_region_;
-
-  task_region_handle() = delete;
-  task_region_handle(const task_region_handle&) = delete;
-  task_region_handle(task_region_handle&&) = delete;
-
-  //! Cancels unstarted pending tasks, and waits for them to respond.
-  ~task_region_handle() noexcept {
-    if (st) {
-      st->abort();
-      st->wait(threads);
-    }
-  }
-
-  task_region_handle& operator=(const task_region_handle&) = delete;
-  task_region_handle& operator=(task_region_handle&&) = delete;
-
-  /*! If the group has no threads, `f` is immediately run before returning.
-  Otherwise, `f` is dispatched to the thread_group associated with `this`
-  region. If `f` is dispatched to another thread, and it throws, the process
-  will immediately terminate. See std::packaged_task for getting exceptions on
-  functions executed on other threads. */
-  template<typename F>
-  void run(F&& f) {
-    if (threads.count() == 0) {
-      f();
-    } else {
-      if (!st || next_id == 0) {
-        create_state();
-      }
-      const state::id this_id = next_id;
-      next_id <<= 1;
-
-      st->track_id(this_id);
-      threads.dispatch(wrapper<F>{this_id, st, std::move(f)});
-    }
-  }
-
-  //! Wait until all functions provided to `run` have completed.
-  void wait() noexcept {
-    if (st) {
-      do_wait();
-    }
-  }
- 
-private:
-  explicit task_region_handle(thread_group& threads_src)
-    : st(nullptr), threads(threads_src), next_id(0) {
-  }
-
-  void create_state();
-  void do_wait() noexcept;
-
-  std::shared_ptr<state> st;
-  thread_group& threads;
-  state::id next_id;
-};
-
-/*! Function for creating a `task_region_handle`, which automatically calls
-`task_region_handle::wait()` before returning. If a `thread_group` is not
-provided, one is created with an optimal number of threads. The callback `f`
-must have the signature `void(task_region_handle&)`. */
-struct task_region_ {
-  template<typename F>
-  void operator()(thread_group& threads, F&& f) const {
-    static_assert(
-      std::is_same<void, typename std::result_of<F(task_region_handle&)>::type>::value,
-      "f cannot have a return value"
-    );
-    task_region_handle region{threads};
-    f(region);
-    region.wait();
-  }
-
-  template<typename F>
-  void operator()(thread_group&& threads, F&& f) const {
-    (*this)(threads, std::forward<F>(f));
-  }
-
-  template<typename F>
-  void operator()(F&& f) const {
-    thread_group threads;
-    (*this)(threads, std::forward<F>(f));
-  }
-};
-
-constexpr const task_region_ task_region{};
-}
diff --git a/src/common/thread_group.cpp b/src/common/thread_group.cpp
deleted file mode 100644
index 691a27a25..000000000
--- a/src/common/thread_group.cpp
+++ /dev/null
@@ -1,153 +0,0 @@
-// Copyright (c) 2014-2017, The Monero Project
-//
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without modification, are
-// permitted provided that the following conditions are met:
-//
-// 1. Redistributions of source code must retain the above copyright notice, this list of
-//    conditions and the following disclaimer.
-//
-// 2. Redistributions in binary form must reproduce the above copyright notice, this list
-//    of conditions and the following disclaimer in the documentation and/or other
-//    materials provided with the distribution.
-//
-// 3. Neither the name of the copyright holder nor the names of its contributors may be
-//    used to endorse or promote products derived from this software without specific
-//    prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
-// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
-// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
-// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
-// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
-// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#include "common/thread_group.h"
-
-#include <boost/thread/locks.hpp>
-#include <cassert>
-#include <limits>
-#include <stdexcept>
-
-#include "cryptonote_config.h"
-#include "common/util.h"
-
-namespace tools
-{
-std::size_t thread_group::optimal() {
-  static_assert(
-    std::numeric_limits<unsigned>::max() <= std::numeric_limits<std::size_t>::max(), 
-    "unexpected truncation"
-  );
-  const std::size_t hardware = get_max_concurrency();
-  return hardware ? (hardware - 1) : 0;
-}
-
-std::size_t thread_group::optimal_with_max(std::size_t count) {
-  return count ? std::min(count - 1, optimal()) : 0;
-}
-
-thread_group::thread_group(std::size_t count) : internal() {
-  if (count) {
-    internal.emplace(count);
-  }
-}
-
-thread_group::data::data(std::size_t count)
-  : threads()
-  , head{nullptr}
-  , last(std::addressof(head))
-  , mutex()
-  , has_work()
-  , stop(false) {
-  threads.reserve(count);
-  boost::thread::attributes attrs;
-  attrs.set_stack_size(THREAD_STACK_SIZE);
-  while (count--) {
-    threads.push_back(boost::thread(attrs, boost::bind(&thread_group::data::run, this)));
-  }
-}
-
-thread_group::data::~data() noexcept {
-  {
-    const boost::unique_lock<boost::mutex> lock(mutex);
-    stop = true;
-  }
-  has_work.notify_all();
-  for (auto& worker : threads) {
-    try {
-      worker.join();
-    }
-    catch(...) {}
-  }
-}
-
-std::unique_ptr<thread_group::data::work> thread_group::data::get_next() noexcept {
-  std::unique_ptr<work> rc = std::move(head.ptr);
-  if (rc != nullptr) {
-    head.ptr = std::move(rc->next.ptr);
-    if (head.ptr == nullptr) {
-      last = std::addressof(head);
-    }
-  }
-  return rc;
-}
-
-bool thread_group::data::try_run_one() noexcept {
-  /* This function and `run()` can both throw when acquiring the lock, or in
-  dispatched function. It is tough to recover from either, particularly the
-  lock case. These functions are marked as noexcept so that if either call
-  throws, the entire process is terminated. Users of the `dispatch` call are
-  expected to make their functions noexcept, or use std::packaged_task to copy
-  exceptions so that the process will continue in all but the most pessimistic
-  cases (std::bad_alloc). This was the existing behavior;
-  `asio::io_service::run` propogates errors from dispatched calls, and uncaught
-  exceptions on threads result in process termination. */
-  std::unique_ptr<work> next = nullptr;
-  {
-    const boost::unique_lock<boost::mutex> lock(mutex);
-    next = get_next();
-  }
-  if (next) {
-    assert(next->f);
-    next->f();
-    return true;
-  }
-  return false;
-}
-
-void thread_group::data::run() noexcept {
-  // see `try_run_one()` source for additional information
-  while (true) {
-    std::unique_ptr<work> next = nullptr;
-    {
-      boost::unique_lock<boost::mutex> lock(mutex);
-      has_work.wait(lock, [this] { return head.ptr != nullptr || stop; });
-      if (stop) {
-        return;
-      }
-      next = get_next();
-    }
-    assert(next != nullptr);
-    assert(next->f);
-    next->f();
-  }
-}
-
-void thread_group::data::dispatch(std::function<void()> f) {
-  std::unique_ptr<work> latest(new work{std::move(f), node{nullptr}});
-  node* const latest_node = std::addressof(latest->next);
-  {
-    const boost::unique_lock<boost::mutex> lock(mutex);
-    assert(last != nullptr);
-    assert(last->ptr == nullptr);
-
-    last->ptr = std::move(latest);
-    last = latest_node;
-  }
-  has_work.notify_one(); 
-}
-}
diff --git a/src/common/thread_group.h b/src/common/thread_group.h
deleted file mode 100644
index 48fd4cd56..000000000
--- a/src/common/thread_group.h
+++ /dev/null
@@ -1,143 +0,0 @@
-// Copyright (c) 2014-2017, The Monero Project
-// 
-// All rights reserved.
-// 
-// Redistribution and use in source and binary forms, with or without modification, are
-// permitted provided that the following conditions are met:
-// 
-// 1. Redistributions of source code must retain the above copyright notice, this list of
-//    conditions and the following disclaimer.
-// 
-// 2. Redistributions in binary form must reproduce the above copyright notice, this list
-//    of conditions and the following disclaimer in the documentation and/or other
-//    materials provided with the distribution.
-// 
-// 3. Neither the name of the copyright holder nor the names of its contributors may be
-//    used to endorse or promote products derived from this software without specific
-//    prior written permission.
-// 
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
-// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
-// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
-// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
-// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
-// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#pragma once
-
-#include <boost/optional/optional.hpp>
-#include <boost/thread/condition_variable.hpp>
-#include <boost/thread/mutex.hpp>
-#include <boost/thread/thread.hpp>
-#include <cstddef>
-#include <functional>
-#include <thread>
-#include <utility>
-#include <vector>
-
-namespace tools 
-{
-//! Manages zero or more threads for work dispatching.
-class thread_group
-{
-public:
-
-  //! \return `get_max_concurrency() ? get_max_concurrency() - 1 : 0`
-  static std::size_t optimal();
-
-  //! \return `count ? min(count - 1, optimal()) : 0`
-  static std::size_t optimal_with_max(std::size_t count);
-
-  //! Create an optimal number of threads.
-  explicit thread_group() : thread_group(optimal()) {}
-
-  //! Create exactly `count` threads.
-  explicit thread_group(std::size_t count);
-
-  thread_group(thread_group const&) = delete;
-  thread_group(thread_group&&) = delete;
-
-  //! Joins threads, but does not necessarily run all dispatched functions.
-  ~thread_group() = default;
-
-  thread_group& operator=(thread_group const&) = delete;
-  thread_group& operator=(thread_group&&) = delete;
-
-  //! \return Number of threads owned by `this` group.
-  std::size_t count() const noexcept {
-    if (internal) {
-      return internal->count();
-    }
-    return 0;
-  }
-
-  //! \return True iff a function was available and executed (on `this_thread`).
-  bool try_run_one() noexcept {
-    if (internal) {
-      return internal->try_run_one();
-    }
-    return false;
-  }
-
-  /*! `f` is invoked immediately if `count() == 0`, otherwise execution of `f`
-  is queued for next available thread. If `f` is queued, any exception leaving
-  that function will result in process termination. Use std::packaged_task if
-  exceptions need to be handled. */
-  template<typename F>
-  void dispatch(F&& f) {
-    if (internal) {
-      internal->dispatch(std::forward<F>(f));
-    }
-    else {
-      f();
-    }
-  }
-
-private:
-  class data {
-  public:
-    data(std::size_t count);
-    ~data() noexcept;
-
-    std::size_t count() const noexcept {
-      return threads.size();
-    }
-
-    bool try_run_one() noexcept;
-    void dispatch(std::function<void()> f);
-
-  private:
-    struct work;
-
-    struct node {
-      std::unique_ptr<work> ptr;
-    };
-
-    struct work {
-      std::function<void()> f;
-      node next;
-    };
-
-    //! Requires lock on `mutex`.
-    std::unique_ptr<work> get_next() noexcept;
-
-    //! Blocks until destructor is invoked, only call from thread.
-    void run() noexcept;
-
-  private:
-    std::vector<boost::thread> threads;
-    node head;
-    node* last;
-    boost::condition_variable has_work;
-    boost::mutex mutex;
-    bool stop;
-  };
-
-private:
-  // optionally construct elements, without separate heap allocation
-  boost::optional<data> internal;
-};
-
-}
diff --git a/src/common/threadpool.cpp b/src/common/threadpool.cpp
new file mode 100644
index 000000000..41d0c25e0
--- /dev/null
+++ b/src/common/threadpool.cpp
@@ -0,0 +1,117 @@
+// Copyright (c) 2017, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#include "common/threadpool.h"
+
+#include <cassert>
+#include <limits>
+#include <stdexcept>
+
+#include "cryptonote_config.h"
+#include "common/util.h"
+
+namespace tools
+{
+threadpool::threadpool() : running(true), active(0) {
+  boost::thread::attributes attrs;
+  attrs.set_stack_size(THREAD_STACK_SIZE);
+  max = tools::get_max_concurrency() * 2;
+  size_t i = max;
+  while(i--) {
+    threads.push_back(boost::thread(attrs, boost::bind(&threadpool::run, this)));
+  }
+}
+
+threadpool::~threadpool() {
+  {
+    const boost::unique_lock<boost::mutex> lock(mutex);
+    running = false;
+    has_work.notify_all();
+  }
+  for (size_t i = 0; i<threads.size(); i++) {
+    threads[i].join();
+  }
+}
+
+void threadpool::submit(waiter *obj, std::function<void()> f) {
+  entry e = {obj, f};
+  boost::unique_lock<boost::mutex> lock(mutex);
+  if (active == max && !queue.empty()) {
+    // if all available threads are already running
+    // and there's work waiting, just run in current thread
+    lock.unlock();
+    f();
+  } else {
+    if (obj)
+      obj->inc();
+    queue.push_back(e);
+    has_work.notify_one();
+  }
+}
+
+int threadpool::get_max_concurrency() {
+  return max / 2;
+}
+
+void threadpool::waiter::wait() {
+  boost::unique_lock<boost::mutex> lock(mt);
+  while(num) cv.wait(lock);
+}
+
+void threadpool::waiter::inc() {
+  const boost::unique_lock<boost::mutex> lock(mt);
+  num++;
+}
+
+void threadpool::waiter::dec() {
+  const boost::unique_lock<boost::mutex> lock(mt);
+  num--;
+  if (!num)
+    cv.notify_one();
+}
+
+void threadpool::run() {
+  boost::unique_lock<boost::mutex> lock(mutex);
+  while (running) {
+    entry e;
+    while(queue.empty() && running)
+      has_work.wait(lock);
+    if (!running) break;
+
+    active++;
+    e = queue.front();
+    queue.pop_front();
+    lock.unlock();
+    e.f();
+
+    if (e.wo)
+      e.wo->dec();
+    lock.lock();
+    active--;
+  }
+}
+}
diff --git a/src/common/threadpool.h b/src/common/threadpool.h
new file mode 100644
index 000000000..1d56d7605
--- /dev/null
+++ b/src/common/threadpool.h
@@ -0,0 +1,87 @@
+// Copyright (c) 2017, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#pragma once
+
+#include <boost/thread/condition_variable.hpp>
+#include <boost/thread/mutex.hpp>
+#include <boost/thread/thread.hpp>
+#include <cstddef>
+#include <functional>
+#include <utility>
+#include <vector>
+
+namespace tools
+{
+//! A global thread pool
+class threadpool
+{
+public:
+  static threadpool& getInstance() {
+    static threadpool instance;
+    return instance;
+  }
+
+  // The waiter lets the caller know when all of its
+  // tasks are completed.
+  class waiter {
+    boost::mutex mt;
+    boost::condition_variable cv;
+    int num;
+    public:
+    void inc();
+    void dec();
+    void wait();  //! Wait for a set of tasks to finish.
+    waiter() : num(0){}
+    ~waiter() { wait(); }
+  };
+
+  // Submit a task to the pool. The waiter pointer may be
+  // NULL if the caller doesn't care to wait for the
+  // task to finish.
+  void submit(waiter *waiter, std::function<void()> f);
+
+  int get_max_concurrency();
+
+  private:
+    threadpool();
+    ~threadpool();
+    typedef struct entry {
+      waiter *wo;
+      std::function<void()> f;
+    } entry;
+    std::deque<entry> queue;
+    boost::condition_variable has_work;
+    boost::mutex mutex;
+    std::vector<boost::thread> threads;
+    int active;
+    int max;
+    bool running;
+    void run();
+};
+
+}