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@@ -0,0 +1,101 @@
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+
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+package bolt
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+
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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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+
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+// flock acquires an advisory lock on a file descriptor.
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+func flock(f *os.File, 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(f.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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+
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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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+
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+// funlock releases an advisory lock on a file descriptor.
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+func funlock(f *os.File) 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(f.Fd()), syscall.F_SETLK, &lock)
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+}
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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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+ // Truncate and fsync to ensure file size metadata is flushed.
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+ // https://github.com/boltdb/bolt/issues/284
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+ if !db.NoGrowSync && !db.readOnly {
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+ if err := db.file.Truncate(int64(sz)); err != nil {
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+ return fmt.Errorf("file resize error: %s", err)
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+ }
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+ if err := db.file.Sync(); err != nil {
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+ return fmt.Errorf("file sync error: %s", err)
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+ }
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+ }
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+
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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)
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+ if err != nil {
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+ return err
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+ }
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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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+
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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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+
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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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+
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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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