Use a threadpool

Instead of constantly creating and destroying threads

src/common/threadpool.cpp

@@ -0,0 +1,113 @@
+// 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();
+  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();
+  }
+}
+
+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--;
+  }
+}
+}