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// 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.
#include "components/services/app_service/public/cpp/icon_coalescer.h"
#include <iterator>
#include <utility>
#include <vector>
#include "base/functional/callback.h"
#include "base/functional/callback_helpers.h"
#include "components/services/app_service/public/cpp/app_types.h"
#include "components/services/app_service/public/cpp/icon_types.h"
namespace apps {
// scoped_refptr<RefCountedReleaser> converts a
// std::unique_ptr<IconLoader::Releaser> to a ref-counted pointer.
class IconCoalescer::RefCountedReleaser
: public base::RefCounted<RefCountedReleaser> {
public:
explicit RefCountedReleaser(std::unique_ptr<IconLoader::Releaser> releaser);
RefCountedReleaser(const RefCountedReleaser&) = delete;
RefCountedReleaser& operator=(const RefCountedReleaser&) = delete;
private:
friend class base::RefCounted<RefCountedReleaser>;
virtual ~RefCountedReleaser();
std::unique_ptr<IconLoader::Releaser> releaser_;
};
IconCoalescer::RefCountedReleaser::RefCountedReleaser(
std::unique_ptr<IconLoader::Releaser> releaser)
: releaser_(std::move(releaser)) {}
IconCoalescer::RefCountedReleaser::~RefCountedReleaser() = default;
IconCoalescer::IconCoalescer(IconLoader* wrapped_loader)
: wrapped_loader_(wrapped_loader), next_sequence_number_(0) {}
IconCoalescer::~IconCoalescer() = default;
std::optional<IconKey> IconCoalescer::GetIconKey(const std::string& id) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
return wrapped_loader_ ? wrapped_loader_->GetIconKey(id) : std::nullopt;
}
std::unique_ptr<IconLoader::Releaser> IconCoalescer::LoadIconFromIconKey(
const std::string& id,
const IconKey& icon_key,
IconType icon_type,
int32_t size_hint_in_dip,
bool allow_placeholder_icon,
apps::LoadIconCallback callback) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
if (!wrapped_loader_) {
std::move(callback).Run(std::make_unique<IconValue>());
return nullptr;
}
if (icon_type != IconType::kUncompressed &&
icon_type != IconType::kStandard) {
return wrapped_loader_->LoadIconFromIconKey(
id, icon_key, icon_type, size_hint_in_dip, allow_placeholder_icon,
std::move(callback));
}
scoped_refptr<RefCountedReleaser> shared_releaser;
IconLoader::Key key(id, icon_key, icon_type, size_hint_in_dip,
allow_placeholder_icon);
auto iter = non_immediate_requests_.find(key);
if (iter != non_immediate_requests_.end()) {
// Coalesce this request with an in-flight one.
//
// |iter->second| is a CallbackAndReleaser. |iter->second.second| is a
// scoped_refptr<RefCountedReleaser>.
shared_releaser = iter->second.second;
} else {
// There is no in-flight request to coalesce with. Instead, forward on the
// request to the wrapped IconLoader.
//
// Calling the |wrapped_loader_|'s LoadIconFromIconKey implementation might
// invoke the passed OnceCallback (binding this class' OnLoadIcon method)
// immediately (now), or at a later time. In both cases, we have to invoke
// (now or later) the |callback| that was passed to this function.
//
// If it's later, then we stash |callback| in |non_immediate_requests_|,
// and look up that same |non_immediate_requests_| during OnLoadIcon.
//
// If it's now, then inserting into the |non_immediate_requests_| would be
// tricky, as we'd have to then unstash the |callback| out of the
// |non_immediate_requests_| (recall that a OnceCallback can be std::move'd
// but not copied), but there are potentially multiple entries with the
// same key, and any multimap iterator might be invalidated if calling into
// the |wrapped_loader_| caused other code to call back into this
// IconCoalescer and mutate that multimap.
//
// Instead, |possibly_immediate_requests_| and |immediate_responses_| keeps
// track of now vs later.
//
// If it's now (if OnLoadIcon is called when the current |seq_num| is in
// |possibly_immediate_requests_|), then OnLoadIcon will populate
// |immediate_responses_| with that |seq_num|. We then run |callback| now,
// right after |wrapped_loader_->LoadIconFromIconKey| returns.
//
// Otherwise we have asynchronously dispatched the underlying icon loading
// request, so store |callback| in |non_immediate_requests_| to be run
// later, when the asynchronous request resolves.
uint64_t seq_num = next_sequence_number_++;
possibly_immediate_requests_.insert(seq_num);
std::unique_ptr<IconLoader::Releaser> unique_releaser =
wrapped_loader_->LoadIconFromIconKey(
id, icon_key, icon_type, size_hint_in_dip, allow_placeholder_icon,
base::BindOnce(&IconCoalescer::OnLoadIcon,
weak_ptr_factory_.GetWeakPtr(), key, seq_num));
possibly_immediate_requests_.erase(seq_num);
auto iv_iter = immediate_responses_.find(seq_num);
if (iv_iter != immediate_responses_.end()) {
IconValuePtr iv = std::move(iv_iter->second);
immediate_responses_.erase(iv_iter);
std::move(callback).Run(std::move(iv));
return unique_releaser;
}
shared_releaser =
base::MakeRefCounted<RefCountedReleaser>(std::move(unique_releaser));
}
non_immediate_requests_.insert(std::make_pair(
key, std::make_pair(std::move(callback), shared_releaser)));
return std::make_unique<IconLoader::Releaser>(
nullptr,
// The callback does nothing explicitly, but after it runs, it implicitly
// decrements the scoped_refptr's shared reference count, and therefore
// possibly deletes the underlying IconLoader::Releaser.
base::DoNothingWithBoundArgs(std::move(shared_releaser)));
}
void IconCoalescer::OnLoadIcon(IconLoader::Key key,
uint64_t sequence_number,
IconValuePtr icon_value) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
if (possibly_immediate_requests_.find(sequence_number) !=
possibly_immediate_requests_.end()) {
immediate_responses_.insert(
std::make_pair(sequence_number, std::move(icon_value)));
return;
}
auto range = non_immediate_requests_.equal_range(key);
auto count = std::distance(range.first, range.second);
if (count <= 0) {
NOTREACHED();
}
// Optimize / simplify the common case.
if (count == 1) {
CallbackAndReleaser callback_and_releaser = std::move(range.first->second);
non_immediate_requests_.erase(range.first, range.second);
std::move(callback_and_releaser.first).Run(std::move(icon_value));
return;
}
// Run every callback in |range|. This is subtle, because an arbitrary
// callback could invoke further methods on |this|, which could mutate
// |non_immediate_requests_|, invalidating |range|'s iterators.
//
// Thus, we first gather the callbacks, then erase the |range|, then run the
// callbacks.
//
// We still run the callbacks, synchronously, instead of posting them on a
// task runner to run later, asynchronously, even though using a task runner
// could avoid having to separate gathering and running the callbacks.
// Synchronous invocation keep the call stack's "how did I get here"
// information, which is useful when debugging.
std::vector<apps::LoadIconCallback> callbacks;
callbacks.reserve(count);
for (auto iter = range.first; iter != range.second; ++iter) {
// |iter->second| is a CallbackAndReleaser. |iter->second.first| is a
// LoadIconCallback.
callbacks.push_back(std::move(iter->second.first));
}
non_immediate_requests_.erase(range.first, range.second);
for (auto& callback : callbacks) {
IconValuePtr iv;
if (--count == 0) {
iv = std::move(icon_value);
} else {
iv = std::make_unique<IconValue>();
iv->icon_type = icon_value->icon_type;
iv->uncompressed = icon_value->uncompressed;
iv->is_placeholder_icon = icon_value->is_placeholder_icon;
}
std::move(callback).Run(std::move(iv));
}
}
} // namespace apps
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