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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 http://mozilla.org/MPL/2.0/. */
#ifndef mozjemalloc_stall_h
#define mozjemalloc_stall_h
#include <optional>
#if defined(MOZ_MEMORY) && defined(XP_WIN)
# include "mozmemory_wrap.h"
#endif
// See
// https://hacks.mozilla.org/2022/11/improving-firefox-stability-with-this-one-weird-trick/
namespace mozilla {
namespace detail {
// Helper for StallAndRetry error messages.
template <typename T>
constexpr bool is_std_optional = false;
template <typename T>
constexpr bool is_std_optional<std::optional<T>> = true;
} // namespace detail
struct StallSpecs {
// Maximum number of retry-attempts before giving up.
size_t maxAttempts;
// Delay time between successive events.
size_t delayMs;
// Retry a fallible operation until it succeeds or until we've run out of
// retries.
//
// Note that this invokes `aDelayFunc` immediately upon being called! It's
// intended for use in the unhappy path, after an initial attempt has failed.
//
// The function type here may be read:
// ```
// fn StallAndRetry<R>(
// delay_func: impl Fn(usize) -> (),
// operation: impl Fn() -> Option<R>,
// ) -> Option<R>;
// ```
//
template <typename DelayFunc, typename OpFunc>
auto StallAndRetry(DelayFunc&& aDelayFunc, OpFunc&& aOperation) const
-> decltype(aOperation()) {
{
// Explicit typecheck for OpFunc, to provide an explicit error message.
using detail::is_std_optional;
static_assert(is_std_optional<decltype(aOperation())>,
"aOperation() must return std::optional");
// (clang's existing error messages suffice for aDelayFunc.)
}
for (size_t i = 0; i < maxAttempts; ++i) {
aDelayFunc(delayMs);
if (const auto opt = aOperation()) {
return opt;
}
}
return std::nullopt;
}
};
#if defined(MOZ_MEMORY) && defined(XP_WIN)
MOZ_JEMALLOC_API StallSpecs GetAllocatorStallSpecs();
MOZ_JEMALLOC_API_NODISCARD void* MozVirtualAlloc(void* lpAddress, size_t dwSize,
uint32_t flAllocationType,
uint32_t flProtect);
#endif
} // namespace mozilla
#endif // mozjemalloc_stall_h
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