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/* -*- 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 */
#ifndef js_SliceBudget_h
#define js_SliceBudget_h
#include "mozilla/Assertions.h"
#include "mozilla/Atomics.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Variant.h"
#include <stdint.h>
#include "jstypes.h"
namespace js {
struct JS_PUBLIC_API TimeBudget {
const mozilla::TimeDuration budget;
mozilla::TimeStamp deadline; // Calculated when SliceBudget is constructed.
explicit TimeBudget(mozilla::TimeDuration duration) : budget(duration) {}
explicit TimeBudget(int64_t milliseconds)
: budget(mozilla::TimeDuration::FromMilliseconds(milliseconds)) {}
void setDeadlineFromNow();
struct JS_PUBLIC_API WorkBudget {
const int64_t budget;
explicit WorkBudget(int64_t work) : budget(work) {}
struct UnlimitedBudget {};
* This class describes a limit to the amount of work to be performed in a GC
* slice, so that we can return to the mutator without pausing for too long. The
* budget may be based on a deadline time or an amount of work to be performed,
* or may be unlimited.
* To reduce the number of gettimeofday calls, we only check the time every 1000
* operations.
class JS_PUBLIC_API SliceBudget {
using InterruptRequestFlag = mozilla::Atomic<bool, mozilla::Relaxed>;
// Whether this slice is running in (predicted to be) idle time.
// Only used for recording in the profile.
bool idle = false;
// Whether this slice was given an extended budget, larger than
// the predicted idle time.
bool extended = false;
static const intptr_t UnlimitedCounter = INTPTR_MAX;
// Most calls to isOverBudget will only check the counter value. Every N
// steps, do a more "expensive" check -- look at the current time and/or
// check the atomic interrupt flag.
static constexpr intptr_t StepsPerExpensiveCheck = 1000;
// Configuration
mozilla::Variant<TimeBudget, WorkBudget, UnlimitedBudget> budget;
// External flag to request the current slice to be interrupted
// (and return isOverBudget() early.) Applies only to time-based budgets.
InterruptRequestFlag* interruptRequested = nullptr;
// How many steps to count before checking the time and possibly the interrupt
// flag.
int64_t counter = StepsPerExpensiveCheck;
// This SliceBudget is considered interrupted from the time isOverBudget()
// finds the interrupt flag set.
bool interrupted = false;
explicit SliceBudget(InterruptRequestFlag* irqPtr)
: budget(UnlimitedBudget()),
counter(irqPtr ? StepsPerExpensiveCheck : UnlimitedCounter) {}
bool checkOverBudget();
// Use to create an unlimited budget.
static SliceBudget unlimited() { return SliceBudget(nullptr); }
// Instantiate as SliceBudget(TimeBudget(n)).
explicit SliceBudget(TimeBudget time,
InterruptRequestFlag* interrupt = nullptr);
explicit SliceBudget(mozilla::TimeDuration duration,
InterruptRequestFlag* interrupt = nullptr)
: SliceBudget(TimeBudget(duration.ToMilliseconds()), interrupt) {}
// Instantiate as SliceBudget(WorkBudget(n)).
explicit SliceBudget(WorkBudget work);
// Register having performed the given number of steps (counted against a
// work budget, or progress towards the next time or callback check).
void step(uint64_t steps = 1) {
MOZ_ASSERT(steps > 0);
counter -= steps;
// Do enough steps to force an "expensive" (time and/or callback) check on
// the next call to isOverBudget. Useful when switching between major phases
// of an operation like a cycle collection.
void stepAndForceCheck() {
if (!isUnlimited()) {
counter = 0;
bool isOverBudget() { return counter <= 0 && checkOverBudget(); }
bool isWorkBudget() const { return<WorkBudget>(); }
bool isTimeBudget() const { return<TimeBudget>(); }
bool isUnlimited() const { return<UnlimitedBudget>(); }
mozilla::TimeDuration timeBudgetDuration() const {
int64_t timeBudget() const { return timeBudgetDuration().ToMilliseconds(); }
int64_t workBudget() const { return<WorkBudget>().budget; }
mozilla::TimeStamp deadline() const {
int describe(char* buffer, size_t maxlen) const;
} // namespace js
#endif /* js_SliceBudget_h */