memory/build/mozmemory_utils.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozjemalloc_utils_h
   8 #define mozjemalloc_utils_h
   9
  10 #include <optional>
  11 #include <type_traits>
  12
  13 #if defined(MOZ_MEMORY) && defined(XP_WIN)
  14 #  include "mozmemory_wrap.h"
  15 #endif
  16
  17 namespace mozilla {
  18
  19 namespace detail {
  20 // Helper for StallAndRetry error messages.
  21 template <typename T>
  22 constexpr bool is_std_optional = false;
  23 template <typename T>
  24 constexpr bool is_std_optional<std::optional<T>> = true;
  25 }  // namespace detail
  26
  27 struct StallSpecs {
  28   // Maximum number of retry-attempts before giving up.
  29   size_t maxAttempts;
  30   // Delay time between successive events.
  31   size_t delayMs;
  32
  33   // Retry a fallible operation until it succeeds or until we've run out of
  34   // retries.
  35   //
  36   // Note that this invokes `aDelayFunc` immediately upon being called! It's
  37   // intended for use in the unhappy path, after an initial attempt has failed.
  38   //
  39   // The function type here may be read:
  40   // ```
  41   // fn StallAndRetry<R>(
  42   //     delay_func: impl Fn(usize) -> (),
  43   //     operation: impl Fn() -> Option<R>,
  44   // ) -> Option<R>;
  45   // ```
  46   //
  47   template <typename DelayFunc, typename OpFunc>
  48   auto StallAndRetry(DelayFunc&& aDelayFunc, OpFunc&& aOperation) const
  49       -> decltype(aOperation()) {
  50     {
  51       // Explicit typecheck for OpFunc, to provide an explicit error message.
  52       using detail::is_std_optional;
  53       static_assert(is_std_optional<decltype(aOperation())>,
  54                     "aOperation() must return std::optional");
  55
  56       // (clang's existing error messages suffice for aDelayFunc.)
  57     }
  58
  59     for (size_t i = 0; i < maxAttempts; ++i) {
  60       aDelayFunc(delayMs);
  61       if (const auto opt = aOperation()) {
  62         return opt;
  63       }
  64     }
  65     return std::nullopt;
  66   }
  67 };
  68
  69 #if defined(MOZ_MEMORY) && defined(XP_WIN)
  70 MOZ_JEMALLOC_API StallSpecs GetAllocatorStallSpecs();
  71 #endif
  72
  73 }  // namespace mozilla
  74
  75 #endif  // mozjemalloc_utils_h