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Locking tweaks.

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This commit is contained in:
Nuno Cruces
2024-01-24 09:58:05 +00:00
parent 3d906d47dd
commit 354242e528
4 changed files with 31 additions and 2 deletions
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7
README.md
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@@ -100,16 +100,21 @@ On BSD Unixes, this module uses
[BSD locks](https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2).
On BSD Unixes, BSD locks are fully compatible with POSIX advisory locks.
On Windows, this module uses `LockFile`, `LockFileEx`, and `UnlockFile`,
On Windows, this module uses `LockFileEx` and `UnlockFileEx`,
like SQLite.
On all other platforms, file locking is not supported, and you must use
[`nolock=1`](https://sqlite.org/uri.html#urinolock)
(or [`immutable=1`](https://sqlite.org/uri.html#uriimmutable))
to open database files.
To use the [`database/sql`](https://pkg.go.dev/database/sql) driver
with `nolock=1` you must disable connection pooling by calling
[`db.SetMaxOpenConns(1)`](https://pkg.go.dev/database/sql#DB.SetMaxOpenConns).
You can use [`vfs.SupportsFileLocking`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs#SupportsFileLocking)
to check if your platform supports file locking.
### Testing
This project aims for [high test coverage](https://github.com/ncruces/go-sqlite3/wiki/Test-coverage-report).

8
vfs/os_nolock.go
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@@ -4,6 +4,14 @@ package vfs
import "os"
// SupportsFileLocking is false on platforms that do not support file locking.
// To open a database file in one such platform,
// 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 = false
func osGetSharedLock(file *os.File) _ErrorCode {
return _IOERR_RDLOCK
}

8
vfs/os_unix2.go → vfs/os_unix_lock.go
View File

@@ -9,6 +9,14 @@ import (
"golang.org/x/sys/unix"
)
// SupportsFileLocking is false on platforms that do not support file locking.
// To open a database file in one such platform,
// 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
func osGetSharedLock(file *os.File) _ErrorCode {
// Test the PENDING lock before acquiring a new SHARED lock.
if pending, _ := osCheckLock(file, _PENDING_BYTE, 1); pending {

10
vfs/os_windows.go
View File

@@ -9,6 +9,14 @@ import (
"golang.org/x/sys/windows"
)
// SupportsFileLocking is false on platforms that do not support file locking.
// To open a database file in one such platform,
// 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
func osGetSharedLock(file *os.File) _ErrorCode {
// Acquire the PENDING lock temporarily before acquiring a new SHARED lock.
rc := osReadLock(file, _PENDING_BYTE, 1, 0)
@@ -49,7 +57,7 @@ func osGetExclusiveLock(file *os.File) _ErrorCode {
func osDowngradeLock(file *os.File, state LockLevel) _ErrorCode {
if state >= LOCK_EXCLUSIVE {
// Release the SHARED lock.
// Release the EXCLUSIVE lock.
osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
// Reacquire the SHARED lock.