View difference between Paste ID: HWBgp6N3 and g0qtxvLS

 Example of dynamic thread pool in boost::asio
-#include <boost/asio.hpp>
+#include <boost/asio.hpp>
-#include <boost/bind.hpp>
+#include <boost/bind.hpp>
-#include <boost/thread.hpp>
+#include <boost/thread.hpp>
-#include <iostream>
+#include <iostream>
-
+
-class thread_pool_checker
+class thread_pool_checker
-  : private boost::noncopyable
+  : private boost::noncopyable
-{
+{
-public:
+public:
-
+
-  thread_pool_checker( boost::asio::io_service& io_service,
+  thread_pool_checker( boost::asio::io_service& io_service,
-                       boost::thread_group& threads,
+                       boost::thread_group& threads,
-                       unsigned int max_threads,
+                       unsigned int max_threads,
-                       long threshold_seconds,
+                       long threshold_seconds,
-                       long periodic_seconds )
+                       long periodic_seconds )
-    : io_service_( io_service ),
+    : io_service_( io_service ),
-      timer_( io_service ),
+      timer_( io_service ),
-      threads_( threads ),
+      threads_( threads ),
-      max_threads_( max_threads ),
+      max_threads_( max_threads ),
-      threshold_seconds_( threshold_seconds ),
+      threshold_seconds_( threshold_seconds ),
-      periodic_seconds_( periodic_seconds )
+      periodic_seconds_( periodic_seconds )
-    {
+    {
-      schedule_check();
+      schedule_check();
-    }
+    }
-
+
-private:
+private:
-
+
-  void schedule_check();
+  void schedule_check();
-  void on_check( const boost::system::error_code& error );
+  void on_check( const boost::system::error_code& error );
-
+
-private:
+private:
-
+
-  boost::asio::io_service&    io_service_;
+  boost::asio::io_service&    io_service_;
-  boost::asio::deadline_timer timer_;
+  boost::asio::deadline_timer timer_;
-  boost::thread_group&        threads_;
+  boost::thread_group&        threads_;
-  unsigned int                max_threads_;
+  unsigned int                max_threads_;
-  long                        threshold_seconds_;
+  long                        threshold_seconds_;
-  long                        periodic_seconds_;
+  long                        periodic_seconds_;
-};
+};
-
+
-void thread_pool_checker::schedule_check()
+void thread_pool_checker::schedule_check()
-{
+{
-  // Thread pool is already at max size.
+  // Thread pool is already at max size.
-  if ( max_threads_ <= threads_.size() )
+  if ( max_threads_ <= threads_.size() )
-  {
+  {
-    std::cout << "Thread pool has reached its max.  Example will shutdown."
+    std::cout << "Thread pool has reached its max.  Example will shutdown."
-              << std::endl;
+              << std::endl;
-    io_service_.stop();
+    io_service_.stop();
-    return;
+    return;
-  }
+  }
-
+
-  // Schedule check to see if pool needs to increase.
+  // Schedule check to see if pool needs to increase.
-  std::cout << "Will check if pool needs to increase in "
+  std::cout << "Will check if pool needs to increase in "
-            << periodic_seconds_ << " seconds." << std::endl;
+            << periodic_seconds_ << " seconds." << std::endl;
-  timer_.expires_from_now( boost::posix_time::seconds( periodic_seconds_ ) );
+  timer_.expires_from_now( boost::posix_time::seconds( periodic_seconds_ ) );
-  timer_.async_wait(
+  timer_.async_wait(
-    boost::bind( &thread_pool_checker::on_check, this,
+    boost::bind( &thread_pool_checker::on_check, this,
-                 boost::asio::placeholders::error ) );
+                 boost::asio::placeholders::error ) );
 }
-
+
-void thread_pool_checker::on_check( const boost::system::error_code& error )
+void thread_pool_checker::on_check( const boost::system::error_code& error )
-{
+{
-  // On error, return early.
+  // On error, return early.
-  if ( error ) return;
+  if ( error ) return;
-
+
-  // Check how long this job was waiting in the service queue.  This
+  // Check how long this job was waiting in the service queue.  This
-  // returns the expiration time relative to now.  Thus, if it expired
+  // returns the expiration time relative to now.  Thus, if it expired
-  // 7 seconds ago, then the delta time is -7 seconds.
+  // 7 seconds ago, then the delta time is -7 seconds.
-  boost::posix_time::time_duration delta = timer_.expires_from_now();
+  boost::posix_time::time_duration delta = timer_.expires_from_now();
-  long wait_in_seconds = -delta.seconds();
+  long wait_in_seconds = -delta.seconds();
-
+
-  // If the time delta is greater than the threshold, then the job
+  // If the time delta is greater than the threshold, then the job
-  // remained in the service queue for too long, so increase the
+  // remained in the service queue for too long, so increase the
-  // thread pool.
+  // thread pool.
-  std::cout << "Job job sat in queue for "
+  std::cout << "Job job sat in queue for "
-            << wait_in_seconds << " seconds." << std::endl;
+            << wait_in_seconds << " seconds." << std::endl;
-  if ( threshold_seconds_ < wait_in_seconds )
+  if ( threshold_seconds_ < wait_in_seconds )
-  {
+  {
-    std::cout << "Increasing thread pool." << std::endl;
+    std::cout << "Increasing thread pool." << std::endl;
-    threads_.create_thread(
+    threads_.create_thread(
-      boost::bind( &boost::asio::io_service::run,
+      boost::bind( &boost::asio::io_service::run,
-                   &io_service_ ) );
+                   &io_service_ ) );
-  }
+  }
-
+
-  // Otherwise, schedule another pool check.
+  // Otherwise, schedule another pool check.
-  run();
+  run();
 }
-
+
-// Busy work functions.
+// Busy work functions.
-void busy_work( boost::asio::io_service&,
+void busy_work( boost::asio::io_service&,
-                unsigned int );
+                unsigned int );
-
+
-void add_busy_work( boost::asio::io_service& io_service,
+void add_busy_work( boost::asio::io_service& io_service,
-                    unsigned int count )
+                    unsigned int count )
-{
+{
-  io_service.post(
+  io_service.post(
-    boost::bind( busy_work,
+    boost::bind( busy_work,
-                 boost::ref( io_service ),
+                 boost::ref( io_service ),
-                 count ) );
+                 count ) );
 }
-
+
-void busy_work( boost::asio::io_service& io_service,
+void busy_work( boost::asio::io_service& io_service,
-                unsigned int count )
+                unsigned int count )
-{
+{
-  boost::this_thread::sleep( boost::posix_time::seconds( 5 ) );
+  boost::this_thread::sleep( boost::posix_time::seconds( 5 ) );
-
+
-  count += 1;
+  count += 1;
-
+
-  // When the count is 3, spawn additional busy work.
+  // When the count is 3, spawn additional busy work.
-  if ( 3 == count )
+  if ( 3 == count )
-  {
+  {
-    add_busy_work( io_service, 0 );
+    add_busy_work( io_service, 0 );
-  }
+  }
-  add_busy_work( io_service, count );
+  add_busy_work( io_service, count );
 }
-
+
-int main()
+int main()
-{
+{
-  using boost::asio::ip::tcp;
+  using boost::asio::ip::tcp;
-
+
-  // Create io service.
+  // Create io service.
-  boost::asio::io_service io_service;
+  boost::asio::io_service io_service;
-
+
-  // Add some busy work to the service.
+  // Add some busy work to the service.
-  add_busy_work( io_service, 0 );
+  add_busy_work( io_service, 0 );
-
+
-  // Create thread group and thread_pool_checker.
+  // Create thread group and thread_pool_checker.
-  boost::thread_group threads;
+  boost::thread_group threads;
-  thread_pool_checker checker( io_service, threads,
+  thread_pool_checker checker( io_service, threads,
-                               3,   // Max pool size.
+                               3,   // Max pool size.
-                               2,   // Create thread if job waits for 2 sec.
+                               2,   // Create thread if job waits for 2 sec.
-                               3 ); // Check if pool needs to grow every 3 sec.
+                               3 ); // Check if pool needs to grow every 3 sec.
-
+
-  // Start running the io service.
+  // Start running the io service.
-  io_service.run();
+  io_service.run();
-
+
-  threads.join_all();
+  threads.join_all();
-
+
-  return 0;
+  return 0;
 }