Added task_region - a fork/join task implementation

1 files changed, 94 insertions, 0 deletions

diff --git a/src/common/task_region.cpp b/src/common/task_region.cpp
new file mode 100644
index 000000000..b53a8376a
--- /dev/null
+++ b/src/common/task_region.cpp
@@ -0,0 +1,94 @@
+// Copyright (c) 2014-2016, 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);
+}
+}