Implement exponential back-off mechanism.

net/url_request/url_request_throttler_manager.cc

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/url_request/url_request_throttler_manager.h"
+
+#include "base/string_util.h"
+
+namespace net {
+
+const unsigned int URLRequestThrottlerManager::kMaximumNumberOfEntries = 1500;
+const unsigned int URLRequestThrottlerManager::kRequestsBetweenCollecting = 200;
+
+URLRequestThrottlerManager* URLRequestThrottlerManager::GetInstance() {
+  return Singleton<URLRequestThrottlerManager>::get();
+}
+
+scoped_refptr<URLRequestThrottlerEntryInterface>
+    URLRequestThrottlerManager::RegisterRequestUrl(const GURL &url) {
+  // Normalize the url.
+  std::string url_id = GetIdFromUrl(url);
+
+  // Periodically garbage collect old entries.
+  GarbageCollectEntriesIfNecessary();
+
+  // Find the entry in the map or create it.
+  scoped_refptr<URLRequestThrottlerEntry>& entry = url_entries_[url_id];
+  if (entry == NULL)
+    entry = new URLRequestThrottlerEntry();
+
+  return entry;
+}
+
+URLRequestThrottlerManager::URLRequestThrottlerManager()
+    : requests_since_last_gc_(0) {
+}
+
+URLRequestThrottlerManager::~URLRequestThrottlerManager() {
+  // Delete all entries.
+  url_entries_.clear();
+}
+
+std::string URLRequestThrottlerManager::GetIdFromUrl(const GURL& url) const {
+  if (!url.is_valid())
+    return url.possibly_invalid_spec();
+
+  if (url_id_replacements_ == NULL) {
+    url_id_replacements_.reset(new GURL::Replacements());
+
+    url_id_replacements_->ClearPassword();
+    url_id_replacements_->ClearUsername();
+    url_id_replacements_->ClearQuery();
+    url_id_replacements_->ClearRef();
+  }
+
+  GURL id = url.ReplaceComponents(*url_id_replacements_);
+  return StringToLowerASCII(id.spec());
+}
+
+void URLRequestThrottlerManager::GarbageCollectEntries() {
+  UrlEntryMap::iterator i = url_entries_.begin();
+
+  while (i != url_entries_.end()) {
+    if ((i->second)->IsEntryOutdated()) {
+      url_entries_.erase(i++);
+    } else {
+      ++i;
+    }
+  }
+
+  // In case something broke we want to make sure not to grow indefinitely.
+  while (url_entries_.size() > kMaximumNumberOfEntries) {
+    url_entries_.erase(url_entries_.begin());
+  }
+}
+
+void URLRequestThrottlerManager::GarbageCollectEntriesIfNecessary() {
+  requests_since_last_gc_++;
+  if (requests_since_last_gc_ < kRequestsBetweenCollecting)
+    return;
+
+  requests_since_last_gc_ = 0;
+  GarbageCollectEntries();
+}
+
+void URLRequestThrottlerManager::OverrideEntryForTests(
+    const GURL& url,
+    URLRequestThrottlerEntry* entry) {
+  if (entry == NULL)
+    return;
+
+  // Normalize the url.
+  std::string url_id = GetIdFromUrl(url);
+
+  // Periodically garbage collect old entries.
+  GarbageCollectEntriesIfNecessary();
+
+  url_entries_[url_id] = entry;
+}
+
+void URLRequestThrottlerManager::EraseEntryForTests(const GURL& url) {
+  // Normalize the url.
+  std::string url_id = GetIdFromUrl(url);
+  url_entries_.erase(url_id);
+}
+
+}  // namespace net