[GitHub] [trafficserver] shukitchan commented on a change in pull request #7623: New rate_limit plugin for simple resource limitations

[GitBox <gi...@apache.org>]

shukitchan commented on a change in pull request #7623:
URL: https://github.com/apache/trafficserver/pull/7623#discussion_r602642295



##########
File path: plugins/experimental/rate_limit/limiter.h
##########
@@ -0,0 +1,162 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include <deque>
+#include <tuple>
+#include <climits>
+#include <atomic>
+#include <cstring>
+#include <cstdio>
+#include <chrono>
+
+#include <ts/ts.h>
+
+constexpr char const PLUGIN_NAME[]  = "rate_limit";
+constexpr unsigned QUEUE_DELAY_TIME = 100; // Examine the queue every 100ms.
+
+using QueueTime = std::chrono::time_point<std::chrono::system_clock>;
+using QueueItem = std::tuple<TSHttpTxn, TSCont, QueueTime>;
+
+///////////////////////////////////////////////////////////////////////////////
+// Configuration object for a rate limiting remap rule.
+//
+class RateLimiter
+{
+public:
+  RateLimiter() : _queue_lock(TSMutexCreate()), _active_lock(TSMutexCreate()) {}
+
+  ~RateLimiter()
+  {
+    if (_action) {
+      TSActionCancel(_action);
+    }
+    if (_queue_cont) {
+      TSContDestroy(_queue_cont);
+    }
+    TSMutexDestroy(_queue_lock);
+    TSMutexDestroy(_active_lock);
+  }
+
+  // Reserve / release a slot from the active connect limits. Reserve will return
+  // false if we are unable to reserve a slot.
+  bool
+  reserve()
+  {
+    TSReleaseAssert(_active <= limit);
+    TSMutexLock(_active_lock);
+    if (_active == limit) {
+      TSMutexUnlock(_active_lock);
+      return false;
+    } else {
+      ++_active;
+      TSDebug(PLUGIN_NAME, "Active txns == %u", active());
+      TSMutexUnlock(_active_lock);
+      return true;
+    }
+  }
+
+  void
+  release()
+  {
+    TSMutexLock(_active_lock);
+    --_active;
+    TSMutexUnlock(_active_lock);
+  }
+
+  // Current size of the active_in connections
+  unsigned
+  active() const
+  {
+    return _active.load();
+  }
+
+  // Current size of the queue
+  unsigned
+  size() const
+  {
+    return _size.load();
+  }
+
+  // Is the queue full (at it's max size)?
+  bool
+  full() const
+  {
+    return (_size == max_queue);
+  }
+
+  void
+  push(TSHttpTxn txnp, TSCont cont)
+  {
+    QueueTime now = std::chrono::system_clock::now();

Review comment:
       Should we use TShrtime() instead? 




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