js/public/SliceBudget.h
author Tom Ritter <tom@mozilla.com>
Mon, 24 Jun 2019 13:20:49 +0000
changeset 537136 828a590988ad2726fcf884fd3af84d1d20ffc141
parent 508251 66eb1f485c1a3ea81372758bc92292c9428b17cd
permissions -rw-r--r--
Bug 1560651 - Correctly set time clamping/jittering for Workers. r=baku, a=RyanVM Differential Revision: https://phabricator.services.mozilla.com/D35629

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef js_SliceBudget_h
#define js_SliceBudget_h

#include "mozilla/TimeStamp.h"

#include <stdint.h>

#include "jstypes.h"

namespace js {

struct JS_PUBLIC_API TimeBudget {
  int64_t budget;

  explicit TimeBudget(int64_t milliseconds) { budget = milliseconds; }
};

struct JS_PUBLIC_API WorkBudget {
  int64_t budget;

  explicit WorkBudget(int64_t work) { budget = work; }
};

/*
 * This class records how much work has been done in a given collection slice,
 * so that we can return before pausing for too long. Some slices are allowed
 * to run for unlimited time, and others are bounded. To reduce the number of
 * gettimeofday calls, we only check the time every 1000 operations.
 */
class JS_PUBLIC_API SliceBudget {
  static mozilla::TimeStamp unlimitedDeadline;
  static const intptr_t unlimitedStartCounter = INTPTR_MAX;

  bool checkOverBudget();

  SliceBudget();

 public:
  // Memory of the originally requested budget. If isUnlimited, neither of
  // these are in use. If deadline==0, then workBudget is valid. Otherwise
  // timeBudget is valid.
  TimeBudget timeBudget;
  WorkBudget workBudget;

  mozilla::TimeStamp deadline;
  intptr_t counter;

  static const intptr_t CounterReset = 1000;

  static const int64_t UnlimitedTimeBudget = -1;
  static const int64_t UnlimitedWorkBudget = -1;

  /* Use to create an unlimited budget. */
  static SliceBudget unlimited() { return SliceBudget(); }

  /* Instantiate as SliceBudget(TimeBudget(n)). */
  explicit SliceBudget(TimeBudget time);

  /* Instantiate as SliceBudget(WorkBudget(n)). */
  explicit SliceBudget(WorkBudget work);

  void makeUnlimited() {
    MOZ_ASSERT(unlimitedDeadline);
    deadline = unlimitedDeadline;
    counter = unlimitedStartCounter;
  }

  void step(intptr_t amt = 1) { counter -= amt; }

  bool isOverBudget() {
    if (counter > 0) {
      return false;
    }
    return checkOverBudget();
  }

  bool isWorkBudget() const { return deadline.IsNull(); }
  bool isTimeBudget() const { return !deadline.IsNull() && !isUnlimited(); }
  bool isUnlimited() const { return deadline == unlimitedDeadline; }

  int describe(char* buffer, size_t maxlen) const;

  static void Init();
};

}  // namespace js

#endif /* js_SliceBudget_h */