chromium/components/services/app_service/public/cpp/icon_coalescer.h

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_SERVICES_APP_SERVICE_PUBLIC_CPP_ICON_COALESCER_H_
#define COMPONENTS_SERVICES_APP_SERVICE_PUBLIC_CPP_ICON_COALESCER_H_

#include <map>
#include <memory>
#include <set>
#include <string>
#include <utility>

#include "base/memory/raw_ptr.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_refptr.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "components/services/app_service/public/cpp/icon_loader.h"

namespace apps {

// An IconLoader that coalesces the apps::mojom::IconType::kUncompressed
// results of another (wrapped) IconLoader.
//
// This is similar to, but different from, an IconCache. Both types are related
// to the LoadIconFromIconKey Mojo call (the request and response), both reduce
// the number of requests made, and both re-use the response for requests with
// the same IconLoader::Key.
//
// An IconCache (another class) applies when the second request is sent *after*
// the first response is received. An IconCoalescer (this class) applies when
// the second request is sent *before* the first response is received (but
// after the first request is sent, obviously).
//
// Caching means that the second (and subsequent) requests can be satisfied
// immediately, sharing the previous response. Coalescing means that the second
// (and subsequent) requests are paused, and when the first request's response
// is finally received, those other requests are un-paused and share the same
// response.
//
// When there are no in-flight requests, a (memory-backed) cache can still have
// a significant memory cost, depending on how aggressive its cache eviction
// policy is, but a (memory-backed) coalescer will have a trivial memory cost.
// Much of its internal state (e.g. maps and multimaps) will be empty.
class IconCoalescer : public IconLoader { … };

}  // namespace apps

#endif  // COMPONENTS_SERVICES_APP_SERVICE_PUBLIC_CPP_ICON_COALESCER_H_