Add a thread pool

1 files changed, 103 insertions, 0 deletions

diff --git a/src/lib/utils/thread_utils/thread_pool.cpp b/src/lib/utils/thread_utils/thread_pool.cpp
new file mode 100644
index 000000000..4ccefe8dc
--- /dev/null
+++ b/src/lib/utils/thread_utils/thread_pool.cpp
@@ -0,0 +1,103 @@
+/*
+* (C) 2019 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/internal/thread_pool.h>
+#include <botan/internal/os_utils.h>
+#include <botan/exceptn.h>
+#include <thread>
+
+namespace Botan {
+
+//static
+Thread_Pool& Thread_Pool::global_instance()
+   {
+   static Thread_Pool g_thread_pool(OS::read_env_variable_sz("BOTAN_THREAD_POOL_SIZE"));
+   return g_thread_pool;
+   }
+
+Thread_Pool::Thread_Pool(size_t pool_size)
+   {
+   if(pool_size == 0)
+      {
+      pool_size = std::thread::hardware_concurrency();
+
+      /*
+      * For large machines don't create too many threads, unless
+      * explicitly asked to by the caller.
+      */
+      if(pool_size > 16)
+         pool_size = 16;
+      }
+
+   if(pool_size <= 1)
+      pool_size = 2;
+
+   m_shutdown = false;
+
+   for(size_t i = 0; i != pool_size; ++i)
+      {
+      m_workers.push_back(std::thread(&Thread_Pool::worker_thread, this));
+      }
+   }
+
+void Thread_Pool::shutdown()
+   {
+      {
+      std::unique_lock<std::mutex> lock(m_mutex);
+
+      if(m_shutdown == true)
+         return;
+
+      m_shutdown = true;
+
+      m_more_tasks.notify_all();
+      }
+
+   for(auto&& thread : m_workers)
+      {
+      thread.join();
+      }
+   m_workers.clear();
+   }
+
+void Thread_Pool::queue_thunk(std::function<void ()> fn)
+   {
+   std::unique_lock<std::mutex> lock(m_mutex);
+
+   if(m_shutdown)
+      throw Invalid_State("Cannot add work after thread pool has shut down");
+
+   m_tasks.push_back(fn);
+   m_more_tasks.notify_one();
+   }
+
+void Thread_Pool::worker_thread()
+   {
+   for(;;)
+      {
+      std::function<void()> task;
+
+         {
+         std::unique_lock<std::mutex> lock(m_mutex);
+         m_more_tasks.wait(lock, [this]{ return m_shutdown || !m_tasks.empty(); });
+
+         if(m_tasks.empty())
+            {
+            if(m_shutdown)
+               return;
+            else
+               continue;
+            }
+
+         task = m_tasks.front();
+         m_tasks.pop_front();
+         }
+
+      task();
+      }
+   }
+
+}