sslobodr | d046be8 | 2019-01-16 10:02:22 -0500 | [diff] [blame^] | 1 | // +build !windows,!plan9,!solaris |
| 2 | |
| 3 | package bolt |
| 4 | |
| 5 | import ( |
| 6 | "fmt" |
| 7 | "os" |
| 8 | "syscall" |
| 9 | "time" |
| 10 | "unsafe" |
| 11 | ) |
| 12 | |
| 13 | // flock acquires an advisory lock on a file descriptor. |
| 14 | func flock(db *DB, mode os.FileMode, exclusive bool, timeout time.Duration) error { |
| 15 | var t time.Time |
| 16 | for { |
| 17 | // If we're beyond our timeout then return an error. |
| 18 | // This can only occur after we've attempted a flock once. |
| 19 | if t.IsZero() { |
| 20 | t = time.Now() |
| 21 | } else if timeout > 0 && time.Since(t) > timeout { |
| 22 | return ErrTimeout |
| 23 | } |
| 24 | flag := syscall.LOCK_SH |
| 25 | if exclusive { |
| 26 | flag = syscall.LOCK_EX |
| 27 | } |
| 28 | |
| 29 | // Otherwise attempt to obtain an exclusive lock. |
| 30 | err := syscall.Flock(int(db.file.Fd()), flag|syscall.LOCK_NB) |
| 31 | if err == nil { |
| 32 | return nil |
| 33 | } else if err != syscall.EWOULDBLOCK { |
| 34 | return err |
| 35 | } |
| 36 | |
| 37 | // Wait for a bit and try again. |
| 38 | time.Sleep(50 * time.Millisecond) |
| 39 | } |
| 40 | } |
| 41 | |
| 42 | // funlock releases an advisory lock on a file descriptor. |
| 43 | func funlock(db *DB) error { |
| 44 | return syscall.Flock(int(db.file.Fd()), syscall.LOCK_UN) |
| 45 | } |
| 46 | |
| 47 | // mmap memory maps a DB's data file. |
| 48 | func mmap(db *DB, sz int) error { |
| 49 | // Map the data file to memory. |
| 50 | b, err := syscall.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED|db.MmapFlags) |
| 51 | if err != nil { |
| 52 | return err |
| 53 | } |
| 54 | |
| 55 | // Advise the kernel that the mmap is accessed randomly. |
| 56 | if err := madvise(b, syscall.MADV_RANDOM); err != nil { |
| 57 | return fmt.Errorf("madvise: %s", err) |
| 58 | } |
| 59 | |
| 60 | // Save the original byte slice and convert to a byte array pointer. |
| 61 | db.dataref = b |
| 62 | db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0])) |
| 63 | db.datasz = sz |
| 64 | return nil |
| 65 | } |
| 66 | |
| 67 | // munmap unmaps a DB's data file from memory. |
| 68 | func munmap(db *DB) error { |
| 69 | // Ignore the unmap if we have no mapped data. |
| 70 | if db.dataref == nil { |
| 71 | return nil |
| 72 | } |
| 73 | |
| 74 | // Unmap using the original byte slice. |
| 75 | err := syscall.Munmap(db.dataref) |
| 76 | db.dataref = nil |
| 77 | db.data = nil |
| 78 | db.datasz = 0 |
| 79 | return err |
| 80 | } |
| 81 | |
| 82 | // NOTE: This function is copied from stdlib because it is not available on darwin. |
| 83 | func madvise(b []byte, advice int) (err error) { |
| 84 | _, _, e1 := syscall.Syscall(syscall.SYS_MADVISE, uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)), uintptr(advice)) |
| 85 | if e1 != 0 { |
| 86 | err = e1 |
| 87 | } |
| 88 | return |
| 89 | } |