src/internal/drain_backoff.hpp
| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | #ifndef DETOURMODKIT_INTERNAL_DRAIN_BACKOFF_HPP | ||
| 2 | #define DETOURMODKIT_INTERNAL_DRAIN_BACKOFF_HPP | ||
| 3 | |||
| 4 | /** | ||
| 5 | * @file internal/drain_backoff.hpp | ||
| 6 | * @brief Paces drains with yields followed by sleeps while another thread exits. | ||
| 7 | */ | ||
| 8 | |||
| 9 | #include <atomic> | ||
| 10 | #include <chrono> | ||
| 11 | #include <cstdint> | ||
| 12 | #include <thread> | ||
| 13 | #include <utility> | ||
| 14 | |||
| 15 | namespace DetourModKit::detail | ||
| 16 | { | ||
| 17 | #if defined(DMK_ENABLE_TEST_SEAMS) | ||
| 18 | /// Exposes yield-tier pauses to the no-pause proofs. | ||
| 19 | extern std::atomic<std::uint64_t> g_drain_backoff_yields; | ||
| 20 | |||
| 21 | /// Counts every sleep-tier pause across all drains, so a proof can observe the escalation. | ||
| 22 | extern std::atomic<std::uint64_t> g_drain_backoff_sleeps; | ||
| 23 | #endif | ||
| 24 | |||
| 25 | /** | ||
| 26 | * @brief Paces one drain loop with a short yield burst followed by 1 ms sleeps. | ||
| 27 | * @details A drained thread can stay descheduled for a long time (a parked callback, a preempted entrant). | ||
| 28 | * Bare yields burn a core in that wait. The sleep tier limits the cost to one wake per millisecond. | ||
| 29 | * One instance belongs to each wait. It allocates nothing and takes no lock. | ||
| 30 | */ | ||
| 31 | class DrainBackoff | ||
| 32 | { | ||
| 33 | public: | ||
| 34 | 4411 | void pause() noexcept | |
| 35 | { | ||
| 36 | 4411 | if (m_yields < YIELD_BURST) | |
| 37 | { | ||
| 38 | 3072 | ++m_yields; | |
| 39 | #if defined(DMK_ENABLE_TEST_SEAMS) | ||
| 40 | g_drain_backoff_yields.fetch_add(1, std::memory_order_relaxed); | ||
| 41 | #endif | ||
| 42 | 3072 | std::this_thread::yield(); | |
| 43 | 3072 | return; | |
| 44 | } | ||
| 45 | #if defined(DMK_ENABLE_TEST_SEAMS) | ||
| 46 | g_drain_backoff_sleeps.fetch_add(1, std::memory_order_relaxed); | ||
| 47 | #endif | ||
| 48 | 1339 | std::this_thread::sleep_for(std::chrono::milliseconds{1}); | |
| 49 | } | ||
| 50 | |||
| 51 | private: | ||
| 52 | static constexpr std::uint32_t YIELD_BURST = 64; | ||
| 53 | std::uint32_t m_yields{0}; | ||
| 54 | }; | ||
| 55 | |||
| 56 | /** | ||
| 57 | * @brief Waits with DrainBackoff pauses until @p count returns zero or @p deadline passes. | ||
| 58 | * @param count A no-throw callable that returns a count comparable with zero. | ||
| 59 | * @return true when the count reached zero. A false return never licenses reclamation: the caller must retain | ||
| 60 | * the undrained resource per [B-73]. | ||
| 61 | */ | ||
| 62 | template <class CountFn> | ||
| 63 | requires(noexcept(std::declval<CountFn &>()() != 0)) | ||
| 64 | 31350 | [[nodiscard]] bool drain_until_zero(CountFn &&count, std::chrono::steady_clock::time_point deadline) noexcept | |
| 65 | { | ||
| 66 | 31350 | DrainBackoff backoff; | |
| 67 | 34096 | while (count() != 0) | |
| 68 | { | ||
| 69 | 2760 | if (std::chrono::steady_clock::now() >= deadline) | |
| 70 | { | ||
| 71 | 14 | return false; | |
| 72 | } | ||
| 73 | 2746 | backoff.pause(); | |
| 74 | } | ||
| 75 | 31336 | return true; | |
| 76 | } | ||
| 77 | } // namespace DetourModKit::detail | ||
| 78 | |||
| 79 | #endif // DETOURMODKIT_INTERNAL_DRAIN_BACKOFF_HPP | ||
| 80 |