package bolt
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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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"golang.org/x/sys/unix"
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)
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// flock acquires an advisory lock on a file descriptor.
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func flock(db *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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var lock syscall.Flock_t
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lock.Start = 0
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lock.Len = 0
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lock.Pid = 0
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lock.Whence = 0
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lock.Pid = 0
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if exclusive {
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lock.Type = syscall.F_WRLCK
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} else {
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lock.Type = syscall.F_RDLCK
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}
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err := syscall.FcntlFlock(db.file.Fd(), syscall.F_SETLK, &lock)
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if err == nil {
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return nil
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} else if err != syscall.EAGAIN {
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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(db *DB) error {
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var lock syscall.Flock_t
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lock.Start = 0
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lock.Len = 0
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lock.Type = syscall.F_UNLCK
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lock.Whence = 0
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return syscall.FcntlFlock(uintptr(db.file.Fd()), syscall.F_SETLK, &lock)
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}
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// mmap memory maps a DB's data file.
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func mmap(db *DB, sz int) error {
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// Map the data file to memory.
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b, err := unix.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED|db.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 := unix.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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db.dataref = b
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db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
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db.datasz = sz
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return nil
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}
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// munmap unmaps a DB's data file from memory.
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func munmap(db *DB) error {
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// Ignore the unmap if we have no mapped data.
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if db.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 := unix.Munmap(db.dataref)
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db.dataref = nil
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db.data = nil
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db.datasz = 0
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return err
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}
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