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Diffstat (limited to 'vendor/google.golang.org/appengine/datastore/transaction.go')
-rw-r--r-- | vendor/google.golang.org/appengine/datastore/transaction.go | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/vendor/google.golang.org/appengine/datastore/transaction.go b/vendor/google.golang.org/appengine/datastore/transaction.go new file mode 100644 index 000000000..a7f3f2b28 --- /dev/null +++ b/vendor/google.golang.org/appengine/datastore/transaction.go @@ -0,0 +1,87 @@ +// Copyright 2011 Google Inc. All rights reserved. +// Use of this source code is governed by the Apache 2.0 +// license that can be found in the LICENSE file. + +package datastore + +import ( + "errors" + + "golang.org/x/net/context" + + "google.golang.org/appengine/internal" + pb "google.golang.org/appengine/internal/datastore" +) + +func init() { + internal.RegisterTransactionSetter(func(x *pb.Query, t *pb.Transaction) { + x.Transaction = t + }) + internal.RegisterTransactionSetter(func(x *pb.GetRequest, t *pb.Transaction) { + x.Transaction = t + }) + internal.RegisterTransactionSetter(func(x *pb.PutRequest, t *pb.Transaction) { + x.Transaction = t + }) + internal.RegisterTransactionSetter(func(x *pb.DeleteRequest, t *pb.Transaction) { + x.Transaction = t + }) +} + +// ErrConcurrentTransaction is returned when a transaction is rolled back due +// to a conflict with a concurrent transaction. +var ErrConcurrentTransaction = errors.New("datastore: concurrent transaction") + +// RunInTransaction runs f in a transaction. It calls f with a transaction +// context tc that f should use for all App Engine operations. +// +// If f returns nil, RunInTransaction attempts to commit the transaction, +// returning nil if it succeeds. If the commit fails due to a conflicting +// transaction, RunInTransaction retries f, each time with a new transaction +// context. It gives up and returns ErrConcurrentTransaction after three +// failed attempts. The number of attempts can be configured by specifying +// TransactionOptions.Attempts. +// +// If f returns non-nil, then any datastore changes will not be applied and +// RunInTransaction returns that same error. The function f is not retried. +// +// Note that when f returns, the transaction is not yet committed. Calling code +// must be careful not to assume that any of f's changes have been committed +// until RunInTransaction returns nil. +// +// Since f may be called multiple times, f should usually be idempotent. +// datastore.Get is not idempotent when unmarshaling slice fields. +// +// Nested transactions are not supported; c may not be a transaction context. +func RunInTransaction(c context.Context, f func(tc context.Context) error, opts *TransactionOptions) error { + xg := false + if opts != nil { + xg = opts.XG + } + attempts := 3 + if opts != nil && opts.Attempts > 0 { + attempts = opts.Attempts + } + for i := 0; i < attempts; i++ { + if err := internal.RunTransactionOnce(c, f, xg); err != internal.ErrConcurrentTransaction { + return err + } + } + return ErrConcurrentTransaction +} + +// TransactionOptions are the options for running a transaction. +type TransactionOptions struct { + // XG is whether the transaction can cross multiple entity groups. In + // comparison, a single group transaction is one where all datastore keys + // used have the same root key. Note that cross group transactions do not + // have the same behavior as single group transactions. In particular, it + // is much more likely to see partially applied transactions in different + // entity groups, in global queries. + // It is valid to set XG to true even if the transaction is within a + // single entity group. + XG bool + // Attempts controls the number of retries to perform when commits fail + // due to a conflicting transaction. If omitted, it defaults to 3. + Attempts int +} |