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package sqlitex
import (
"context"
"runtime"
"github.com/go-llsqlite/crawshaw"
)
// GetSnapshot returns a Snapshot that should remain available for reads until
// it is garbage collected.
//
// This sets aside a Conn from the Pool with an open read transaction until the
// Snapshot is garbage collected or the Pool is closed. Thus, until the
// returned Snapshot is garbage collected, the Pool will have one fewer Conn,
// and it should not be possible for the WAL to be checkpointed beyond the
// point of the Snapshot.
//
// See sqlite.Conn.GetSnapshot and sqlite.Snapshot for more details.
func (p *Pool) GetSnapshot(ctx context.Context, schema string) (*sqlite.Snapshot, error) {
conn := p.Get(ctx)
if conn == nil {
return nil, context.Canceled
}
conn.SetInterrupt(nil)
s, release, err := conn.GetSnapshot(schema)
if err != nil {
return nil, err
}
snapshotGCd := make(chan struct{})
runtime.SetFinalizer(s, nil)
runtime.SetFinalizer(s, func(s *sqlite.Snapshot) {
// Free the C resources associated with the Snapshot.
s.Free()
close(snapshotGCd)
})
go func() {
select {
case <-p.closed:
case <-snapshotGCd:
}
// Allow the WAL to be checkpointed past the point of
// the Snapshot.
release()
// Return the conn to the Pool for reuse.
p.Put(conn)
}()
return s, nil
}
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