90 lines
2.1 KiB
Go
90 lines
2.1 KiB
Go
// +build !windows,!plan9,!solaris
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package pages
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import (
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"fmt"
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"os"
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"syscall"
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"time"
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"unsafe"
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)
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// flock acquires an advisory lock on a file descriptor.
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func flock(pb *DB, mode os.FileMode, exclusive bool, timeout time.Duration) error {
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var t time.Time
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for {
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// If we're beyond our timeout then return an error.
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// This can only occur after we've attempted a flock once.
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if t.IsZero() {
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t = time.Now()
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} else if timeout > 0 && time.Since(t) > timeout {
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return ErrTimeout
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}
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flag := syscall.LOCK_SH
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if exclusive {
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flag = syscall.LOCK_EX
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}
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// Otherwise attempt to obtain an exclusive lock.
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err := syscall.Flock(int(pb.file.Fd()), flag|syscall.LOCK_NB)
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if err == nil {
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return nil
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} else if err != syscall.EWOULDBLOCK {
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return err
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}
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// Wait for a bit and try again.
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time.Sleep(50 * time.Millisecond)
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}
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}
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// funlock releases an advisory lock on a file descriptor.
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func funlock(pb *DB) error {
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return syscall.Flock(int(pb.file.Fd()), syscall.LOCK_UN)
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}
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// mmap memory maps a PageBuf's data file.
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func mmap(pb *DB, sz int) error {
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// Map the data file to memory.
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b, err := syscall.Mmap(int(pb.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED|pb.MmapFlags)
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if err != nil {
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return err
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}
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// Advise the kernel that the mmap is accessed randomly.
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if err := madvise(b, syscall.MADV_RANDOM); err != nil {
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return fmt.Errorf("madvise: %s", err)
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}
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// Save the original byte slice and convert to a byte array pointer.
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pb.dataref = b
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pb.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
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pb.datasz = sz
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return nil
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}
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// munmap unmaps a PageBuf's data file from memory.
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func munmap(pb *DB) error {
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// Ignore the unmap if we have no mapped data.
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if pb.dataref == nil {
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return nil
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}
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// Unmap using the original byte slice.
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err := syscall.Munmap(pb.dataref)
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pb.dataref = nil
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pb.data = nil
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pb.datasz = 0
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return err
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}
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// NOTE: This function is copied from stdlib because it is not available on darwin.
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func madvise(b []byte, advice int) (err error) {
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_, _, e1 := syscall.Syscall(syscall.SYS_MADVISE, uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)), uintptr(advice))
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if e1 != 0 {
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err = e1
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}
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return
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}
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