// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "content/browser/renderer_host/spare_render_process_host_manager.h"

#include "base/check.h"
#include "base/debug/dump_without_crashing.h"
#include "base/memory/memory_pressure_monitor.h"
#include "base/no_destructor.h"
#include "content/browser/renderer_host/render_process_host_impl.h"
#include "content/browser/site_instance_impl.h"
#include "content/public/browser/browser_context.h"
#include "content/public/browser/render_process_host.h"
#include "content/public/common/content_client.h"

namespace content {

SpareRenderProcessHostManager::SpareRenderProcessHostManager() = default;
SpareRenderProcessHostManager::~SpareRenderProcessHostManager() = default;

// static
SpareRenderProcessHostManager& SpareRenderProcessHostManager::GetInstance() {
  static base::NoDestructor<SpareRenderProcessHostManager> s_instance;
  return *s_instance;
}

void SpareRenderProcessHostManager::WarmupSpareRenderProcessHost(
    BrowserContext* browser_context) {
  if (spare_render_process_host_ &&
      spare_render_process_host_->GetBrowserContext() == browser_context) {
    DCHECK_EQ(browser_context->GetDefaultStoragePartition(),
              spare_render_process_host_->GetStoragePartition());
    return;  // Nothing to warm up.
  }

  CleanupSpareRenderProcessHost();

  // Don't create a spare renderer for a BrowserContext that is in the
  // process of shutting down.
  if (browser_context->ShutdownStarted()) {
    // Create a crash dump to help us assess what scenarios trigger this
    // path to be taken.
    // TODO(acolwell): Remove this call once are confident we've eliminated
    // any problematic callers.
    base::debug::DumpWithoutCrashing();

    return;
  }

  // Don't create a spare renderer if we're using --single-process or if we've
  // got too many processes. See also ShouldTryToUseExistingProcessHost in
  // this file.
  if (RenderProcessHost::run_renderer_in_process() ||
      RenderProcessHostImpl::GetProcessCountForLimit() >=
          RenderProcessHostImpl::GetMaxRendererProcessCount()) {
    return;
  }

  // Don't create a spare renderer when the system is under load.  This is
  // currently approximated by only looking at the memory pressure.  See also
  // https://crbug.com/852905.
  auto* memory_monitor = base::MemoryPressureMonitor::Get();
  if (memory_monitor &&
      memory_monitor->GetCurrentPressureLevel() >=
          base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE) {
    return;
  }

  spare_render_process_host_ = RenderProcessHostImpl::CreateRenderProcessHost(
      browser_context, nullptr /* site_instance */);
  spare_render_process_host_->AddObserver(this);
  spare_render_process_host_->Init();

  // The spare render process isn't ready, so wait and do the "spare render
  // process changed" callback in RenderProcessReady().
}

RenderProcessHost*
SpareRenderProcessHostManager::MaybeTakeSpareRenderProcessHost(
    BrowserContext* browser_context,
    SiteInstanceImpl* site_instance) {
  // Give embedder a chance to disable using a spare RenderProcessHost for
  // certain SiteInstances.  Some navigations, such as to NTP or extensions,
  // require passing command-line flags to the renderer process at process
  // launch time, but this cannot be done for spare RenderProcessHosts, which
  // are started before it is known which navigation might use them.  So, a
  // spare RenderProcessHost should not be used in such cases.
  //
  // Note that exempting NTP and extensions from using the spare process might
  // also happen via HasProcess check below (which returns true for
  // process-per-site SiteInstances if the given process-per-site process
  // already exists).  Despite this potential overlap, it is important to do
  // both kinds of checks (to account for other non-ntp/extension
  // process-per-site scenarios + to work correctly even if
  // ShouldUseSpareRenderProcessHost starts covering non-process-per-site
  // scenarios).
  bool embedder_allows_spare_usage =
      GetContentClient()->browser()->ShouldUseSpareRenderProcessHost(
          browser_context, site_instance->GetSiteInfo().site_url());

  // The spare RenderProcessHost always launches with JIT enabled, so if JIT
  // is disabled for the site then it's not possible to use this as the JIT
  // policy will differ.
  if (GetContentClient()->browser()->IsJitDisabledForSite(
          browser_context, site_instance->GetSiteInfo().process_lock_url())) {
    embedder_allows_spare_usage = false;
  }

  // We shouldn't use the spare if:
  // 1. The SiteInstance has already got an associated process.  This is
  //    important to avoid taking and then immediately discarding the spare
  //    for process-per-site scenarios (which the HasProcess call below
  //    accounts for).  Note that HasProcess will return false and allow using
  //    the spare if the given process-per-site process hasn't been launched.
  // 2. The SiteInstance has opted out of using the spare process.
  bool site_instance_allows_spare_usage =
      !site_instance->HasProcess() &&
      site_instance->CanAssociateWithSpareProcess();

  bool hosts_pdf_content = site_instance->GetSiteInfo().is_pdf();

  // Get the StoragePartition for |site_instance|.  Note that this might be
  // different than the default StoragePartition for |browser_context|.
  StoragePartition* site_storage =
      browser_context->GetStoragePartition(site_instance);

  // Log UMA metrics.
  using SpareProcessMaybeTakeAction =
      RenderProcessHostImpl::SpareProcessMaybeTakeAction;
  SpareProcessMaybeTakeAction action =
      SpareProcessMaybeTakeAction::kNoSparePresent;
  if (!spare_render_process_host_) {
    action = SpareProcessMaybeTakeAction::kNoSparePresent;
  } else if (browser_context !=
             spare_render_process_host_->GetBrowserContext()) {
    action = SpareProcessMaybeTakeAction::kMismatchedBrowserContext;
  } else if (!spare_render_process_host_->InSameStoragePartition(
                 site_storage)) {
    action = SpareProcessMaybeTakeAction::kMismatchedStoragePartition;
  } else if (!embedder_allows_spare_usage) {
    action = SpareProcessMaybeTakeAction::kRefusedByEmbedder;
  } else if (!site_instance_allows_spare_usage) {
    action = SpareProcessMaybeTakeAction::kRefusedBySiteInstance;
  } else if (hosts_pdf_content) {
    action = SpareProcessMaybeTakeAction::kRefusedForPdfContent;
  } else {
    action = SpareProcessMaybeTakeAction::kSpareTaken;
  }
  UMA_HISTOGRAM_ENUMERATION(
      "BrowserRenderProcessHost.SpareProcessMaybeTakeAction", action);

  // Decide whether to take or drop the spare process.
  RenderProcessHost* returned_process = nullptr;
  if (spare_render_process_host_ &&
      browser_context == spare_render_process_host_->GetBrowserContext() &&
      spare_render_process_host_->InSameStoragePartition(site_storage) &&
      !site_instance->IsGuest() && embedder_allows_spare_usage &&
      site_instance_allows_spare_usage && !hosts_pdf_content) {
    CHECK(spare_render_process_host_->HostHasNotBeenUsed());

    // If the spare process ends up getting killed, the spare manager should
    // discard the spare RPH, so if one exists, it should always be live here.
    CHECK(spare_render_process_host_->IsInitializedAndNotDead());

    DCHECK_EQ(SpareProcessMaybeTakeAction::kSpareTaken, action);
    returned_process = spare_render_process_host_;
    ReleaseSpareRenderProcessHost();
  } else if (!RenderProcessHostImpl::IsSpareProcessKeptAtAllTimes()) {
    // If the spare shouldn't be kept around, then discard it as soon as we
    // find that the current spare was mismatched.
    CleanupSpareRenderProcessHost();
  } else if (RenderProcessHostImpl::GetProcessCountForLimit() >=
             RenderProcessHostImpl::GetMaxRendererProcessCount()) {
    // Drop the spare if we are at a process limit and the spare wasn't taken.
    // This helps avoid process reuse.
    CleanupSpareRenderProcessHost();
  }

  return returned_process;
}

void SpareRenderProcessHostManager::PrepareForFutureRequests(
    BrowserContext* browser_context) {
  if (RenderProcessHostImpl::IsSpareProcessKeptAtAllTimes()) {
    // Always keep around a spare process for the most recently requested
    // |browser_context|.
    WarmupSpareRenderProcessHost(browser_context);
  } else {
    // Discard the ignored (probably non-matching) spare so as not to waste
    // resources.
    CleanupSpareRenderProcessHost();
  }
}

void SpareRenderProcessHostManager::CleanupSpareRenderProcessHost() {
  if (spare_render_process_host_) {
    // Stop observing the process, to avoid getting notifications as a
    // consequence of the Cleanup call below - such notification could call
    // back into CleanupSpareRenderProcessHost leading to stack overflow.
    spare_render_process_host_->RemoveObserver(this);

    // Make sure the RenderProcessHost object gets destroyed.
    if (!spare_render_process_host_->AreRefCountsDisabled()) {
      spare_render_process_host_->Cleanup();
    }

    // Drop reference to the RenderProcessHost object.
    spare_render_process_host_ = nullptr;
    spare_render_process_host_changed_callback_list_.Notify(nullptr);
  }
}

base::CallbackListSubscription
SpareRenderProcessHostManager::RegisterSpareRenderProcessHostChangedCallback(
    const base::RepeatingCallback<void(RenderProcessHost*)>& cb) {
  // Do an initial notification, as the subscriber will need to know what the
  // current spare host is.
  cb.Run(spare_render_process_host_.get());
  return spare_render_process_host_changed_callback_list_.Add(cb);
}

void SpareRenderProcessHostManager::ReleaseSpareRenderProcessHost() {
  CHECK(spare_render_process_host_);

  spare_render_process_host_->RemoveObserver(this);
  spare_render_process_host_ = nullptr;
  spare_render_process_host_changed_callback_list_.Notify(nullptr);
}

void SpareRenderProcessHostManager::RenderProcessReady(
    RenderProcessHost* host) {
  CHECK_EQ(spare_render_process_host_, host);
  spare_render_process_host_changed_callback_list_.Notify(
      spare_render_process_host_);
}

void SpareRenderProcessHostManager::RenderProcessExited(
    RenderProcessHost* host,
    const ChildProcessTerminationInfo& info) {
  CHECK_EQ(spare_render_process_host_, host);
  CleanupSpareRenderProcessHost();
}

void SpareRenderProcessHostManager::RenderProcessHostDestroyed(
    RenderProcessHost* host) {
  CHECK_EQ(spare_render_process_host_, host);
  ReleaseSpareRenderProcessHost();
}

}  // namespace content