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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chrome/browser/ui/thumbnails/thumbnail_scheduler_impl.h"
#include <algorithm>
#include "base/memory/raw_ptr.h"
// static
constexpr int ThumbnailSchedulerImpl::kMaxTotalCaptures;
// static
constexpr int ThumbnailSchedulerImpl::kMaxLowPriorityCaptures;
struct ThumbnailSchedulerImpl::TabSchedulingData {
TabCapturePriority priority = TabCapturePriority::kNone;
};
struct ThumbnailSchedulerImpl::TabNode : public base::LinkNode<TabNode> {
raw_ptr<TabCapturer> capturer = nullptr;
TabSchedulingData data;
bool is_capturing = false;
};
ThumbnailSchedulerImpl::ThumbnailSchedulerImpl(int max_total_captures,
int max_low_priority_captures)
: max_total_captures_(max_total_captures),
max_low_priority_captures_(max_low_priority_captures) {
DCHECK_GT(max_total_captures_, 0);
DCHECK_GE(max_total_captures_, max_low_priority_captures_);
}
ThumbnailSchedulerImpl::~ThumbnailSchedulerImpl() = default;
void ThumbnailSchedulerImpl::AddTab(TabCapturer* tab) {
auto result = tabs_.emplace(tab, TabNode{});
DCHECK(result.second) << "tab added more than once";
result.first->second.capturer = tab;
}
void ThumbnailSchedulerImpl::RemoveTab(TabCapturer* tab) {
int num_removed = tabs_.erase(tab);
DCHECK_EQ(1, num_removed) << "removed a tab that was never added";
}
void ThumbnailSchedulerImpl::SetTabCapturePriority(
TabCapturer* tab,
TabCapturePriority priority) {
TabNode* const node = GetTabNode(tab);
if (node->data.priority == priority) {
return;
}
const TabSchedulingData old_data = node->data;
node->data.priority = priority;
Schedule(node, old_data);
}
void ThumbnailSchedulerImpl::Schedule(TabNode* tab_node,
const TabSchedulingData& old_data) {
// Scheduling is run after each tab priority change. So, at most one
// tab may be scheduled, at most one tab may be descheduled, or both.
TabNode* scheduled_tab = nullptr;
TabNode* descheduled_tab = nullptr;
// First, move the tab node to the correct list and update the
// capturing counts.
if (tab_node->next()) {
tab_node->RemoveFromList();
}
if (tab_node->is_capturing) {
switch (old_data.priority) {
case TabCapturePriority::kNone:
// TODO(crbug.com/347770670): ThumbnailSchedulerImpl may not correctly
// deschedule discarded tabs when their priority transitions to kNone.
// This should be corrected once WebContentsDiscard lands and the old
// discarding code path is cleaned up.
NOTREACHED(base::NotFatalUntil::M142);
return;
case TabCapturePriority::kLow:
lo_prio_capture_count_ -= 1;
break;
case TabCapturePriority::kHigh:
hi_prio_capture_count_ -= 1;
break;
}
}
switch (tab_node->data.priority) {
case TabCapturePriority::kNone:
descheduled_tab = tab_node;
break;
case TabCapturePriority::kLow:
if (tab_node->is_capturing) {
lo_prio_capturing_.Append(tab_node);
lo_prio_capture_count_ += 1;
} else {
lo_prio_waiting_.Append(tab_node);
}
break;
case TabCapturePriority::kHigh:
if (tab_node->is_capturing) {
hi_prio_capturing_.Append(tab_node);
hi_prio_capture_count_ += 1;
} else {
hi_prio_waiting_.Append(tab_node);
}
break;
}
// First schedule a high priority tab if any are waiting, subject to
// the maximum. Note that at most one may be schedulable. Prior to
// this scheduling update, all possible high priority tabs were
// scheduled. The only conditions leading to scheduling a new one are:
//
// 1. |tab| was newly prioritized and less than |max_total_captures_|
// tabs are capturing, or
//
// 2. |tab| was deprioritized and other tabs are waiting in
// |high_priority_wait_queue_|.
//
// So pick one tab from |high_priority_wait_queue_| and schedule it.
// In case (1) this is guaranteed to be |tab|.
if (hi_prio_capture_count_ < max_total_captures_ &&
!hi_prio_waiting_.empty()) {
scheduled_tab = hi_prio_waiting_.head()->value();
scheduled_tab->RemoveFromList();
hi_prio_capturing_.Append(scheduled_tab);
hi_prio_capture_count_ += 1;
}
const int lo_prio_quota = std::min(
max_low_priority_captures_, max_total_captures_ - hi_prio_capture_count_);
// A high priority tab may have been deprioritized, so the low
// priority quota may be off by one.
DCHECK_LE(lo_prio_capture_count_, lo_prio_quota + 1);
// A new high priority capture may preempt an existing low priority one. This
// happens in two cases:
//
// 1. |tab| was set to high priority when at the max total captures, or
//
// 2. |tab| was changed from high to low priority while capturing and
// there are other high priority tabs waiting.
//
// In this case, deschedule any low priority tab. Otherwise, schedule
// a new one if below the quota. Note the latter cannot happen if a
// high priority tab was scheduled above.
if (lo_prio_capture_count_ > lo_prio_quota) {
DCHECK_EQ(descheduled_tab, nullptr);
descheduled_tab = lo_prio_capturing_.tail()->value();
descheduled_tab->RemoveFromList();
lo_prio_waiting_.Append(descheduled_tab);
lo_prio_capture_count_ -= 1;
} else if (lo_prio_capture_count_ < lo_prio_quota &&
!lo_prio_waiting_.empty()) {
DCHECK_EQ(scheduled_tab, nullptr);
scheduled_tab = lo_prio_waiting_.head()->value();
scheduled_tab->RemoveFromList();
lo_prio_capturing_.Append(scheduled_tab);
lo_prio_capture_count_ += 1;
}
if (descheduled_tab) {
descheduled_tab->capturer->SetCapturePermittedByScheduler(false);
descheduled_tab->is_capturing = false;
}
if (scheduled_tab) {
scheduled_tab->capturer->SetCapturePermittedByScheduler(true);
scheduled_tab->is_capturing = true;
}
}
ThumbnailSchedulerImpl::TabNode* ThumbnailSchedulerImpl::GetTabNode(
TabCapturer* tab) {
auto it = tabs_.find(tab);
CHECK(it != tabs_.end())
<< "referenced tab that is not registered with scheduler";
return &it->second;
}
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