Adding a previews IO-thread blacklist

components/previews/core/previews_black_list.cc

Index: components/previews/core/previews_black_list.cc
diff --git a/components/previews/core/previews_black_list.cc b/components/previews/core/previews_black_list.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e9561e5d8c70aace6fdfca59a9766508b8bd0c9d
--- /dev/null
+++ b/components/previews/core/previews_black_list.cc
@@ -0,0 +1,151 @@
+// Copyright 2016 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 "components/previews/core/previews_black_list.h"
+
+#include "base/bind.h"
+#include "base/memory/ptr_util.h"
+#include "base/optional.h"
+#include "base/time/clock.h"
+#include "base/time/time.h"
+#include "components/previews/core/previews_black_list_item.h"
+#include "components/previews/core/previews_experiments.h"
+#include "url/gurl.h"
+
+namespace previews {
+
+PreviewsBlackList::PreviewsBlackList(
+    std::unique_ptr<PreviewsOptOutStore> opt_out_store,
+    std::unique_ptr<base::Clock> clock)
+    : loaded_(false),
+      opt_out_store_(std::move(opt_out_store)),
+      clock_(std::move(clock)),
+      weak_factory_(this) {
+  if (opt_out_store_) {
+    opt_out_store_->LoadBlackList(base::Bind(
+        &PreviewsBlackList::LoadBlackListDone, weak_factory_.GetWeakPtr()));
+  } else {
+    LoadBlackListDone(base::MakeUnique<BlackListItemMap>());
+  }
+}
+
+PreviewsBlackList::~PreviewsBlackList() {}
+
+void PreviewsBlackList::AddPreviewNavigation(const GURL& url,
+                                             bool opt_out,
+                                             PreviewsType type) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(url.has_host());
+  // If the |black_list_item_map_| has been loaded from |opt_out_store_|,
+  // synchronous operations will be accurate. Otherwise, queue the task to run
+  // asynchronously.
+  if (loaded_) {
+    AddPreviewNavigationSync(url, opt_out, type);
+  } else {
+    QueuePendingTask(base::Bind(&PreviewsBlackList::AddPreviewNavigationSync,
+                                base::Unretained(this), url, opt_out, type));
+  }
+}
+
+void PreviewsBlackList::AddPreviewNavigationSync(const GURL& url,
+                                                 bool opt_out,
+                                                 PreviewsType type) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(url.has_host());
+  DCHECK(loaded_);
+  std::string host_name = url.host();
+  base::Time now = clock_->Now();
+  PreviewsBlackListItem* item = GetBlackListItem(host_name);
+  if (!item) {
+    item = CreateBlackListItem(host_name);
+  }
+  item->AddPreviewNavigation(opt_out, now);
+  DCHECK_LE(black_list_item_map_->size(),
+            params::MaxInMemoryHostsInBlackList());
+  if (!opt_out_store_)
+    return;
+  opt_out_store_->AddPreviewNavigation(opt_out, host_name, type, now);
+}
+
+bool PreviewsBlackList::IsLoadedAndAllowed(const GURL& url,
+                                           PreviewsType type) const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(url.has_host());
+  std::string host_name = url.host();

[tbansal1, 2016/09/22 21:12:27]

nit: you can move this statement after the if-conditional.
Also, you can just combine it with the statement
PreviewsBlackListItem* black_list_item = GetBlackListItem(host_name);

[RyanSturm, 2016/09/23 17:23:24]

Done.

+  if (!loaded_)
+    return false;
+  PreviewsBlackListItem* black_list_item = GetBlackListItem(host_name);
+  return !black_list_item || !black_list_item->IsBlackListed(clock_->Now());
+}
+
+void PreviewsBlackList::QueuePendingTask(QueueClosure callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(!loaded_);
+  DCHECK(!callback.is_null());
+  pending_callbacks_.emplace(callback);
+}
+
+void PreviewsBlackList::LoadBlackListDone(
+    std::unique_ptr<BlackListItemMap> black_list_item_map) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_LE(black_list_item_map->size(), params::MaxInMemoryHostsInBlackList());
+  loaded_ = true;
+  black_list_item_map_ = std::move(black_list_item_map);
+
+  // Run all pending tasks. |loaded_| may change if ClearBlackList is queued.
+  while (pending_callbacks_.size() > 0 && loaded_) {
+    pending_callbacks_.front().Run();
+    pending_callbacks_.pop();
+  }
+}
+
+PreviewsBlackListItem* PreviewsBlackList::GetBlackListItem(
+    const std::string& host_name) const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(loaded_);
+  BlackListItemMap::iterator iter = black_list_item_map_->find(host_name);
+  if (iter != black_list_item_map_->end())
+    return iter->second.get();
+  return nullptr;
+}
+
+PreviewsBlackListItem* PreviewsBlackList::CreateBlackListItem(
+    const std::string& host_name) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(loaded_);
+  DCHECK(black_list_item_map_->find(host_name) == black_list_item_map_->end());

[tbansal1, 2016/09/22 21:12:27]

s/DCHECK/DHECK_EQ/
or
DCHECK(!GetBlackListItem(host_name));

[RyanSturm, 2016/09/23 17:23:24]

Done.

+  if (black_list_item_map_->size() >= params::MaxInMemoryHostsInBlackList())
+    EvictOldestOptOut();
+  DCHECK_LT(black_list_item_map_->size(),
+            params::MaxInMemoryHostsInBlackList());
+  PreviewsBlackListItem* black_list_item = new PreviewsBlackListItem(
+      params::MaxStoredHistoryLengthForBlackList(),
+      params::BlackListOptOutThreshold(), params::BlackListDuration());
+  black_list_item_map_->operator[](host_name) =
+      base::WrapUnique(black_list_item);
+  return black_list_item;
+}
+
+void PreviewsBlackList::EvictOldestOptOut() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(loaded_);
+  // TODO(ryansturm): Add UMA. crbug.com/647717
+  BlackListItemMap::iterator item_to_delete = black_list_item_map_->end();
+  base::Time oldest_opt_out = clock_->Now();
+  for (BlackListItemMap::iterator iter = black_list_item_map_->begin();
+       iter != black_list_item_map_->end(); ++iter) {
+    if (!iter->second->most_recent_opt_out_time()) {
+      // If there is no opt out time, this is a good choice to evict.
+      item_to_delete = iter;
+      break;
+    }
+    if (iter->second->most_recent_opt_out_time().value() < oldest_opt_out) {
+      oldest_opt_out = iter->second->most_recent_opt_out_time().value();
+      item_to_delete = iter;
+    }
+  }
+  black_list_item_map_->erase(item_to_delete);
+}
+
+}  // namespace previews