mirror of
https://github.com/matrix-org/dendrite
synced 2024-12-13 11:33:13 +01:00
9d53351dc2
* Offset updates take place using TransactionWriter * Refactor TransactionWriter in current state server * Refactor TransactionWriter in federation sender * Refactor TransactionWriter in key server * Refactor TransactionWriter in media API * Refactor TransactionWriter in server key API * Refactor TransactionWriter in sync API * Refactor TransactionWriter in user API * Fix deadlocking Sync API tests * Un-deadlock device database * Fix appservice API * Rename TransactionWriters to Writers * Move writers up a layer in sync API * Document sqlutil.Writer interface * Add note to Writer documentation
46 lines
1.9 KiB
Go
46 lines
1.9 KiB
Go
package sqlutil
|
|
|
|
import "database/sql"
|
|
|
|
// The Writer interface is designed to solve the problem of how
|
|
// to handle database writes for database engines that don't allow
|
|
// concurrent writes, e.g. SQLite.
|
|
//
|
|
// The interface has a single Do function which takes an optional
|
|
// database parameter, an optional transaction parameter and a
|
|
// required function parameter. The Writer will call the function
|
|
// provided when it is safe to do so, optionally providing a
|
|
// transaction to use.
|
|
//
|
|
// Depending on the combination of parameters provided, the Writer
|
|
// will behave in one of three ways:
|
|
//
|
|
// 1. `db` provided, `txn` provided:
|
|
//
|
|
// The Writer will call f() when it is safe to do so. The supplied
|
|
// "txn" will ALWAYS be passed through to f(). Use this when you
|
|
// already have a transaction open.
|
|
//
|
|
// 2. `db` provided, `txn` not provided (nil):
|
|
//
|
|
// The Writer will open a new transaction on the provided database
|
|
// and then will call f() when it is safe to do so. The new
|
|
// transaction will ALWAYS be passed through to f(). Use this if
|
|
// you plan to perform more than one SQL query within f().
|
|
//
|
|
// 3. `db` not provided (nil), `txn` not provided (nil):
|
|
//
|
|
// The Writer will call f() when it is safe to do so, but will
|
|
// not make any attempt to open a new database transaction or to
|
|
// pass through an existing one. The "txn" parameter within f()
|
|
// will ALWAYS be nil in this mode. This is useful if you just
|
|
// want to perform a single query on an already-prepared statement
|
|
// without the overhead of opening a new transaction to do it in.
|
|
//
|
|
// You MUST take particular care not to call Do() from within f()
|
|
// on the same Writer, or it will likely result in a deadlock.
|
|
type Writer interface {
|
|
// Queue up one or more database write operations within the
|
|
// provided function to be executed when it is safe to do so.
|
|
Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error
|
|
}
|