txn.go

package clientv3

import (

    "sync"

    pb "github.com/coreos/etcd/etcdserver/etcdserverpb"

    "golang.org/x/net/context"

    "google.golang.org/grpc"

)

// Txn is the interface that wraps mini-transactions.

//

//     Tx.If(

//      Compare(Value(k1), ">", v1),

//      Compare(Version(k1), "=", 2)

//     ).Then(

//      OpPut(k2,v2), OpPut(k3,v3)

//     ).Else(

//      OpPut(k4,v4), OpPut(k5,v5)

//     ).Commit()

//

type Txn interface {

    // If takes a list of comparison. If all comparisons passed in succeed,

    // the operations passed into Then() will be executed. Or the operations

    // passed into Else() will be executed.

    If(cs ...Cmp) Txn

    // Then takes a list of operations. The Ops list will be executed, if the

    // comparisons passed in If() succeed.

    Then(ops ...Op) Txn

    // Else takes a list of operations. The Ops list will be executed, if the

    // comparisons passed in If() fail.

    Else(ops ...Op) Txn

    // Commit tries to commit the transaction.

    Commit() (*TxnResponse, error)

    // TODO: add a Do for shortcut the txn without any condition?

}

type txn struct {

    kv  *kv

    ctx context.Context

    mu    sync.Mutex

    cif   bool

    cthen bool

    celse bool

    isWrite bool

    cmps []*pb.Compare

    sus []*pb.RequestOp

    fas []*pb.RequestOp

}

func (txn *txn) If(cs ...Cmp) Txn {

    txn.mu.Lock()

    defer txn.mu.Unlock()

    if txn.cif {

        panic("cannot call If twice!")

    }

    if txn.cthen {

        panic("cannot call If after Then!")

    }

    if txn.celse {

        panic("cannot call If after Else!")

    }

    txn.cif = true

    for i := range cs {

        txn.cmps = append(txn.cmps, (*pb.Compare)(&cs[i]))

    }

    return txn

}

func (txn *txn) Then(ops ...Op) Txn {

    txn.mu.Lock()

    defer txn.mu.Unlock()

    if txn.cthen {

        panic("cannot call Then twice!")

    }

    if txn.celse {

        panic("cannot call Then after Else!")

    }

    txn.cthen = true

    for _, op := range ops {

        txn.isWrite = txn.isWrite || op.isWrite()

        txn.sus = append(txn.sus, op.toRequestOp())

    }

    return txn

}

func (txn *txn) Else(ops ...Op) Txn {

    txn.mu.Lock()

    defer txn.mu.Unlock()

    if txn.celse {

        panic("cannot call Else twice!")

    }

    txn.celse = true

    for _, op := range ops {

        txn.isWrite = txn.isWrite || op.isWrite()

        txn.fas = append(txn.fas, op.toRequestOp())

    }

    return txn

}

func (txn *txn) Commit() (*TxnResponse, error) {

    txn.mu.Lock()

    defer txn.mu.Unlock()

    for {

        resp, err := txn.commit()

        if err == nil {

            return resp, err

        }

        if isHaltErr(txn.ctx, err) {

            return nil, toErr(txn.ctx, err)

        }

        if txn.isWrite {

            return nil, toErr(txn.ctx, err)

        }

    }

}

func (txn *txn) commit() (*TxnResponse, error) {

    r := &pb.TxnRequest{Compare: txn.cmps, Success: txn.sus, Failure: txn.fas}

    var opts []grpc.CallOption

    if !txn.isWrite {

        opts = []grpc.CallOption{grpc.FailFast(false)}

    }

    resp, err := txn.kv.remote.Txn(txn.ctx, r, opts...)

    if err != nil {

        return nil, err

    }

    return (*TxnResponse)(resp), nil

}