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35 lines
1 KiB
Go
35 lines
1 KiB
Go
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// +build cgo
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package fs
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// #cgo CFLAGS: -O3
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//
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// #include <stdint.h> // for uintptr_t
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// #include <string.h> // for memcpy
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//
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// // The memcpy_wrapper allows avoiding memory allocations during calls from Go.
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// // See https://github.com/golang/go/issues/24450 .
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// static void memcpy_wrapper(uintptr_t dst, uintptr_t src, size_t n) {
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// memcpy((void*)dst, (void*)src, n);
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// }
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import "C"
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import (
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"runtime"
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"unsafe"
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)
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// copyMmap copies len(dst) bytes from src to dst.
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func copyMmap(dst, src []byte) {
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// Copy data from mmap'ed src via cgo call in order to protect from goroutine stalls
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// when the copied data isn't available in RAM, so the OS triggers reading the data from file.
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// See https://medium.com/@valyala/mmap-in-go-considered-harmful-d92a25cb161d for details.
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dstPtr := C.uintptr_t(uintptr(unsafe.Pointer(&dst[0])))
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srcPtr := C.uintptr_t(uintptr(unsafe.Pointer(&src[0])))
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C.memcpy_wrapper(dstPtr, srcPtr, C.size_t(len(dst)))
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// Prevent from GC'ing src or dst during C.memcpy_wrapper call.
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runtime.KeepAlive(src)
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runtime.KeepAlive(dst)
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}
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