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|
//go:build (darwin || linux) && (amd64 || arm64 || riscv64) && !(sqlite3_flock || sqlite3_noshm || sqlite3_nosys)
package vfs
import (
"context"
"io"
"os"
"github.com/ncruces/go-sqlite3/internal/util"
"github.com/tetratelabs/wazero/api"
"golang.org/x/sys/unix"
)
// SupportsSharedMemory is false on platforms that do not support shared memory.
// To use [WAL without shared-memory], you need to set [EXCLUSIVE locking mode].
//
// [WAL without shared-memory]: https://sqlite.org/wal.html#noshm
// [EXCLUSIVE locking mode]: https://sqlite.org/pragma.html#pragma_locking_mode
const SupportsSharedMemory = true
const (
_SHM_NLOCK = 8
_SHM_BASE = 120
_SHM_DMS = _SHM_BASE + _SHM_NLOCK
)
func (f *vfsFile) SharedMemory() SharedMemory { return f.shm }
// NewSharedMemory returns a shared-memory WAL-index
// backed by a file with the given path.
// It will return nil if shared-memory is not supported,
// or not appropriate for the given flags.
// Only [OPEN_MAIN_DB] databases may need a WAL-index.
// You must ensure all concurrent accesses to a database
// use shared-memory instances created with the same path.
func NewSharedMemory(path string, flags OpenFlag) SharedMemory {
if flags&OPEN_MAIN_DB == 0 || flags&(OPEN_DELETEONCLOSE|OPEN_MEMORY) != 0 {
return nil
}
return &vfsShm{
path: path,
readOnly: flags&OPEN_READONLY != 0,
}
}
type vfsShm struct {
*os.File
path string
regions []*util.MappedRegion
readOnly bool
}
func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, error) {
// Ensure size is a multiple of the OS page size.
if int(size)&(unix.Getpagesize()-1) != 0 {
return 0, _IOERR_SHMMAP
}
if s.File == nil {
var flag int
if s.readOnly {
flag = unix.O_RDONLY
} else {
flag = unix.O_RDWR
}
f, err := os.OpenFile(s.path,
flag|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
if err != nil {
return 0, _CANTOPEN
}
s.File = f
}
// Dead man's switch.
if lock, rc := osGetLock(s.File, _SHM_DMS, 1); rc != _OK {
return 0, _IOERR_LOCK
} else if lock == unix.F_WRLCK {
return 0, _BUSY
} else if lock == unix.F_UNLCK {
if s.readOnly {
return 0, _READONLY_CANTINIT
}
if rc := osWriteLock(s.File, _SHM_DMS, 1, 0); rc != _OK {
return 0, rc
}
if err := s.Truncate(0); err != nil {
return 0, _IOERR_SHMOPEN
}
}
if rc := osReadLock(s.File, _SHM_DMS, 1, 0); rc != _OK {
return 0, rc
}
// Check if file is big enough.
o, err := s.Seek(0, io.SeekEnd)
if err != nil {
return 0, _IOERR_SHMSIZE
}
if n := (int64(id) + 1) * int64(size); n > o {
if !extend {
return 0, nil
}
err := osAllocate(s.File, n)
if err != nil {
return 0, _IOERR_SHMSIZE
}
}
var prot int
if s.readOnly {
prot = unix.PROT_READ
} else {
prot = unix.PROT_READ | unix.PROT_WRITE
}
r, err := util.MapRegion(ctx, mod, s.File, int64(id)*int64(size), size, prot)
if err != nil {
return 0, err
}
s.regions = append(s.regions, r)
return r.Ptr, nil
}
func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) error {
// Argument check.
if n <= 0 || offset < 0 || offset+n > _SHM_NLOCK {
panic(util.AssertErr())
}
switch flags {
case
_SHM_LOCK | _SHM_SHARED,
_SHM_LOCK | _SHM_EXCLUSIVE,
_SHM_UNLOCK | _SHM_SHARED,
_SHM_UNLOCK | _SHM_EXCLUSIVE:
//
default:
panic(util.AssertErr())
}
if n != 1 && flags&_SHM_EXCLUSIVE == 0 {
panic(util.AssertErr())
}
switch {
case flags&_SHM_UNLOCK != 0:
return osUnlock(s.File, _SHM_BASE+int64(offset), int64(n))
case flags&_SHM_SHARED != 0:
return osReadLock(s.File, _SHM_BASE+int64(offset), int64(n), 0)
case flags&_SHM_EXCLUSIVE != 0:
return osWriteLock(s.File, _SHM_BASE+int64(offset), int64(n), 0)
default:
panic(util.AssertErr())
}
}
func (s *vfsShm) shmUnmap(delete bool) {
if s.File == nil {
return
}
// Unmap regions.
for _, r := range s.regions {
r.Unmap()
}
clear(s.regions)
s.regions = s.regions[:0]
// Close the file.
defer s.Close()
if delete {
os.Remove(s.Name())
}
s.File = nil
}
|
