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//go:build (linux || darwin || windows || freebsd || openbsd || netbsd || dragonfly || illumos || sqlite3_flock) && !sqlite3_nosys
package vfs
import "github.com/ncruces/go-sqlite3/internal/util"
// SupportsFileLocking is false on platforms that do not support file locking.
// To open a database file on those platforms,
// you need to use the [nolock] or [immutable] URI parameters.
//
// [nolock]: https://sqlite.org/uri.html#urinolock
// [immutable]: https://sqlite.org/uri.html#uriimmutable
const SupportsFileLocking = true
const (
_PENDING_BYTE = 0x40000000
_RESERVED_BYTE = (_PENDING_BYTE + 1)
_SHARED_FIRST = (_PENDING_BYTE + 2)
_SHARED_SIZE = 510
)
func (f *vfsFile) Lock(lock LockLevel) error {
// Argument check. SQLite never explicitly requests a pending lock.
if lock != LOCK_SHARED && lock != LOCK_RESERVED && lock != LOCK_EXCLUSIVE {
panic(util.AssertErr())
}
switch {
case f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE:
// Connection state check.
panic(util.AssertErr())
case f.lock == LOCK_NONE && lock > LOCK_SHARED:
// We never move from unlocked to anything higher than a shared lock.
panic(util.AssertErr())
case f.lock != LOCK_SHARED && lock == LOCK_RESERVED:
// A shared lock is always held when a reserved lock is requested.
panic(util.AssertErr())
}
// If we already have an equal or more restrictive lock, do nothing.
if f.lock >= lock {
return nil
}
// Do not allow any kind of write-lock on a read-only database.
if f.readOnly && lock >= LOCK_RESERVED {
return _IOERR_LOCK
}
switch lock {
case LOCK_SHARED:
// Must be unlocked to get SHARED.
if f.lock != LOCK_NONE {
panic(util.AssertErr())
}
if rc := osGetSharedLock(f.File); rc != _OK {
return rc
}
f.lock = LOCK_SHARED
return nil
case LOCK_RESERVED:
// Must be SHARED to get RESERVED.
if f.lock != LOCK_SHARED {
panic(util.AssertErr())
}
if rc := osGetReservedLock(f.File); rc != _OK {
return rc
}
f.lock = LOCK_RESERVED
return nil
case LOCK_EXCLUSIVE:
// Must be SHARED, RESERVED or PENDING to get EXCLUSIVE.
if f.lock <= LOCK_NONE || f.lock >= LOCK_EXCLUSIVE {
panic(util.AssertErr())
}
reserved := f.lock == LOCK_RESERVED
// A PENDING lock is needed before acquiring an EXCLUSIVE lock.
if f.lock < LOCK_PENDING {
// If we're already RESERVED, we can block indefinitely,
// since only new readers may briefly hold the PENDING lock.
if rc := osGetPendingLock(f.File, reserved /* block */); rc != _OK {
return rc
}
f.lock = LOCK_PENDING
}
// We already have PENDING, so we're just waiting for readers to leave.
// If we were RESERVED, we can wait for a little while, before invoking
// the busy handler; we will only do this once.
if rc := osGetExclusiveLock(f.File, reserved /* wait */); rc != _OK {
return rc
}
f.lock = LOCK_EXCLUSIVE
return nil
default:
panic(util.AssertErr())
}
}
func (f *vfsFile) Unlock(lock LockLevel) error {
// Argument check.
if lock != LOCK_NONE && lock != LOCK_SHARED {
panic(util.AssertErr())
}
// Connection state check.
if f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE {
panic(util.AssertErr())
}
// If we don't have a more restrictive lock, do nothing.
if f.lock <= lock {
return nil
}
switch lock {
case LOCK_SHARED:
rc := osDowngradeLock(f.File, f.lock)
f.lock = LOCK_SHARED
return rc
case LOCK_NONE:
rc := osReleaseLock(f.File, f.lock)
f.lock = LOCK_NONE
return rc
default:
panic(util.AssertErr())
}
}
func (f *vfsFile) CheckReservedLock() (bool, error) {
// Connection state check.
if f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE {
panic(util.AssertErr())
}
if f.lock >= LOCK_RESERVED {
return true, nil
}
return osCheckReservedLock(f.File)
}
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