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79 lines
2.7 KiB
C++
79 lines
2.7 KiB
C++
// SPDX-License-Identifier: MIT
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/*
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$info$
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category: code buffer ~ Thread shared code buffer management
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tags: backend|shared
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$end_info$
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*/
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#pragma once
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#include <FEXCore/fextl/memory.h>
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#include <FEXCore/Utils/SignalScopeGuards.h>
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#include <FEXCore/Utils/TypeDefines.h>
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#include <cstddef>
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#include <cstdint>
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namespace FEXCore {
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struct GuestToHostMap;
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}
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namespace FEXCore::CPU {
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struct CodeBuffer {
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uint8_t* Ptr;
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size_t AllocatedSize; // including guard page; see UsableSize()
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fextl::unique_ptr<GuestToHostMap> LookupCache;
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CodeBuffer(size_t Size);
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CodeBuffer(const CodeBuffer&) = delete;
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CodeBuffer& operator=(const CodeBuffer&) = delete;
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CodeBuffer(CodeBuffer&& oth) = delete;
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CodeBuffer& operator=(CodeBuffer&&) = delete;
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~CodeBuffer();
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/// Returns the number of bytes available for storing code
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size_t UsableSize() const {
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return AllocatedSize - FEXCore::Utils::FEX_PAGE_SIZE;
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}
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};
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/**
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* A manager that coordinates access to the CodeBuffer used for compiling new code across threads.
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*
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* The CodeBuffer is managed as a partially persistent data structure:
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* - Exactly one CodeBuffer is now designated as "active", which means data can be appended to it
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* - Lossy modifications to the active CodeBuffer will not invalidate any data in use by other threads (which is what enables save CodeBuffer sharing across threads)
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* - Instead, such lossy modifications trigger a new "version" of the data in the modifying thread. Old versions of the CodeBuffer persist as read-only data for use by the other threads.
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* - The other threads can update their version of the CodeBuffer. This will decrease the reference count and eventually trigger deallocation of the old version
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*/
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class SharedCodeBufferManager {
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public:
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// Get the CodeBuffer that was most recently allocated.
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// This is the only CodeBuffer that data may be written to.
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fextl::shared_ptr<CodeBuffer> GetLatest();
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// Allocate a new CodeBuffer with geometric growth up to an internal maximum.
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// Subsequent calls to GetLatest will point to the returned buffer.
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fextl::shared_ptr<CodeBuffer> StartLargerCodeBuffer();
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// Allocate a new CodeBuffer with maximum internal size.
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// Subsequent calls to GetLatest will point to the returned buffer.
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fextl::shared_ptr<CodeBuffer> StartMaximalCodeBuffer();
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// Write offset into the latest CodeBuffer
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std::size_t LatestOffset {};
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// Protects writes to the latest CodeBuffer and changes to LatestOffset
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FEXCore::ForkableUniqueMutex CodeBufferWriteMutex;
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virtual void OnCodeBufferAllocated(const std::shared_ptr<CodeBuffer>&) {};
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private:
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fextl::shared_ptr<CodeBuffer> Latest;
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fextl::shared_ptr<CodeBuffer> AllocateNew(size_t Size);
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};
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} // namespace FEXCore::CPU
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