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WritePriorityMutex: Fix rare case of dropped read waiter wakes #5161

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Merged
Sonicadvance1 merged 1 commit into from
Dec 27, 2025
+6 −6
Merged

WritePriorityMutex: Fix rare case of dropped read waiter wakes #5161

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12 changes: 6 additions & 6 deletions FEXCore/Source/Utils/WritePriorityMutex.h
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Original file line number Diff line number Diff line change
Expand Up @@ -353,14 +353,14 @@ class Mutex final {
}

constexpr static uint32_t WRITE_OWNED_BIT = 1U << 31;
constexpr static uint32_t READ_WAITER_BIT = 1U << 15;
constexpr static uint32_t READ_WAITER_BIT = 1U << 30;
constexpr static uint32_t WRITE_WAITER_OFFSET = 16;
constexpr static uint32_t WRITE_WAITER_INCREMENT = 1U << WRITE_WAITER_OFFSET;
constexpr static uint32_t READ_OWNER_INCREMENT = 1;

// Count masks
constexpr static uint32_t WRITE_WAITER_COUNT_MASK = 0x7FFFU << WRITE_WAITER_OFFSET;
constexpr static uint32_t READ_OWNER_COUNT_MASK = 0x7FFFU;
constexpr static uint32_t WRITE_WAITER_COUNT_MASK = 0x3FFFU << WRITE_WAITER_OFFSET;
constexpr static uint32_t READ_OWNER_COUNT_MASK = 0xFFFFU;

// Independent futex bit-set masks.
// Wait for readers to drain.
Expand All @@ -373,9 +373,9 @@ class Mutex final {

// Layout:
// Bits[31]: Write-lock bit.
// Bits[30:16]: Write-waiter count.
// Bits[15]: Read-waiter bit.
// Bits[14:0]: Read-owner count.
// Bits[30]: Read-waiter bit.
// Bits[29:16]: Write-waiter count.
// Bits[15:0]: Read-owner count.
uint32_t Futex {};
};
} // namespace FEXCore::Utils::WritePriorityMutex
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