1 files changed, 131 insertions, 0 deletions
diff --git a/src/cpp/server/dynamic_thread_pool.cc b/src/cpp/server/dynamic_thread_pool.cc
new file mode 100644
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+++ b/src/cpp/server/dynamic_thread_pool.cc
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+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. 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
+ * OWNER 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 <grpc++/impl/sync.h>
+#include <grpc++/impl/thd.h>
+#include <grpc++/dynamic_thread_pool.h>
+
+namespace grpc {
+DynamicThreadPool::DynamicThread::DynamicThread(DynamicThreadPool *pool):
+  pool_(pool),
+  thd_(new grpc::thread(&DynamicThreadPool::DynamicThread::ThreadFunc, this)) {
+}
+DynamicThreadPool::DynamicThread::~DynamicThread() {
+  thd_->join();
+  thd_.reset();
+}
+
+void DynamicThreadPool::DynamicThread::ThreadFunc() {
+  pool_->ThreadFunc();
+  // Now that we have killed ourselves, we should reduce the thread count
+  grpc::unique_lock<grpc::mutex> lock(pool_->mu_);
+  pool_->nthreads_--;
+  // Move ourselves to dead list
+  pool_->dead_threads_.push_back(this);
+
+  if ((pool_->shutdown_) && (pool_->nthreads_ == 0)) {
+    pool_->shutdown_cv_.notify_one();
+  }
+}
+  
+void DynamicThreadPool::ThreadFunc() {
+  for (;;) {
+    // Wait until work is available or we are shutting down.
+    grpc::unique_lock<grpc::mutex> lock(mu_);
+    if (!shutdown_ && callbacks_.empty()) {
+      // If there are too many threads waiting, then quit this thread
+      if (threads_waiting_ >= reserve_threads_) {
+	break;
+      }
+      threads_waiting_++;
+      cv_.wait(lock);
+      threads_waiting_--;
+    }
+    // Drain callbacks before considering shutdown to ensure all work
+    // gets completed.
+    if (!callbacks_.empty()) {
+      auto cb = callbacks_.front();
+      callbacks_.pop();
+      lock.unlock();
+      cb();
+    } else if (shutdown_) {
+      break;
+    }
+  }
+}
+
+DynamicThreadPool::DynamicThreadPool(int reserve_threads) :
+  shutdown_(false), reserve_threads_(reserve_threads), nthreads_(0),
+  threads_waiting_(0) {
+  for (int i = 0; i < reserve_threads_; i++) {
+    grpc::lock_guard<grpc::mutex> lock(mu_);
+    nthreads_++;
+    new DynamicThread(this);
+  }
+}
+
+void DynamicThreadPool::ReapThreads(std::list<DynamicThread*>* tlist) {
+  for (auto t = tlist->begin(); t != tlist->end(); t = tlist->erase(t)) {
+    delete *t;    
+  }
+}
+  
+DynamicThreadPool::~DynamicThreadPool() {
+  grpc::unique_lock<grpc::mutex> lock(mu_);
+  shutdown_ = true;
+  cv_.notify_all();
+  while (nthreads_ != 0) {
+    shutdown_cv_.wait(lock);
+  }
+  ReapThreads(&dead_threads_);
+}
+
+void DynamicThreadPool::Add(const std::function<void()>& callback) {
+  grpc::lock_guard<grpc::mutex> lock(mu_);
+  // Add works to the callbacks list
+  callbacks_.push(callback);
+  // Increase pool size or notify as needed
+  if (threads_waiting_ == 0) {
+    // Kick off a new thread
+    nthreads_++;
+    new DynamicThread(this);
+  } else {
+    cv_.notify_one();
+  }
+  // Also use this chance to harvest dead threads
+  if (!dead_threads_.empty()) {
+    ReapThreads(&dead_threads_);
+  }
+}
+
+}  // namespace grpc