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package database
import (
"database/sql"
"encoding/json"
"errors"
)
// Atomically check the lock status of a state and lock it if unlocked. Returns
// true if the function locked the state, otherwise returns false and the lock
// parameter is updated to the value of the existing lock
func (db *DB) SetLockOrGetExistingLock(name string, lock any) (bool, error) {
tx, err := db.Begin()
if err != nil {
return false, err
}
defer func() {
if err != nil {
_ = tx.Rollback()
}
}()
var lockData []byte
if err = tx.QueryRowContext(db.ctx, `SELECT lock FROM states WHERE name = ?;`, name).Scan(&lockData); err != nil {
if errors.Is(err, sql.ErrNoRows) {
if lockData, err = json.Marshal(lock); err != nil {
return false, err
}
_, err = tx.ExecContext(db.ctx, `INSERT INTO states(name, lock) VALUES (?, json(?))`, name, lockData)
if err != nil {
return false, err
}
err = tx.Commit()
return true, err
} else {
return false, err
}
}
if lockData != nil {
_ = tx.Rollback()
err = json.Unmarshal(lockData, lock)
return false, err
}
if lockData, err = json.Marshal(lock); err != nil {
return false, err
}
_, err = tx.ExecContext(db.ctx, `UPDATE states SET lock = json(?) WHERE name = ?;`, lockData, name)
if err != nil {
return false, err
}
err = tx.Commit()
return true, err
}
func (db *DB) Unlock(name, lock any) (bool, error) {
data, err := json.Marshal(lock)
if err != nil {
return false, err
}
result, err := db.Exec(`UPDATE states SET lock = NULL WHERE name = ? and lock = json(?);`, name, data)
if err != nil {
return false, err
}
n, err := result.RowsAffected()
return n == 1, err
}
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