Source code for transaction.interfaces

##############################################################################
#
# Copyright (c) 2001, 2002 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################

from zope.interface import Attribute
from zope.interface import Interface


[docs]class ITransactionManager(Interface): """An object that manages a sequence of transactions. Applications use transaction managers to establish transaction boundaries. A transaction manager supports the "context manager" protocol: Its `__enter__` begins a new transaction; its `__exit__` commits the current transaction if no exception has occured; otherwise, it aborts it. """ explicit = Attribute( """Explicit mode indicator. This is true if the transaction manager is in explicit mode. In explicit mode, transactions must be begun explicitly, by calling `begin` and ended explicitly by calling `commit` or `abort`. .. versionadded:: 2.1.0 """) def begin(): """Explicitly begin and return a new transaction. If an existing transaction is in progress and the transaction manager not in explicit mode, the previous transaction will be aborted. If an existing transaction is in progress and the transaction manager is in explicit mode, an `AlreadyInTransaction` exception will be raised.. The `~ISynchronizer.newTransaction` method of registered synchronizers is called, passing the new transaction object. Note that when not in explicit mode, transactions may be started implicitly without calling `begin`. In that case, ``newTransaction`` isn't called because the transaction manager doesn't know when to call it. The transaction is likely to have begun long before the transaction manager is involved. (Conceivably the `commit` and `abort` methods could call `begin`, but they don't.) """ def get(): """Get the current transaction. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def commit(): """Commit the current transaction. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def abort(): """Abort the current transaction. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def doom(): """Doom the current transaction. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def isDoomed(): """Return True if the current transaction is doomed, otherwise False. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def savepoint(optimistic=False): """Create a savepoint from the current transaction. If the optimistic argument is true, then data managers that don't support savepoints can be used, but an error will be raised if the savepoint is rolled back. An `ISavepoint` object is returned. In explicit mode, if a transaction hasn't begun, a `NoTransaction` exception will be raised. """ def registerSynch(synch): """Register an `ISynchronizer`. Synchronizers are notified about some major events in a transaction's life. See `ISynchronizer` for details. If a synchronizer registers while there is an active transaction, its ``newTransaction`` method will be called with the active transaction. """ def unregisterSynch(synch): """Unregister an `ISynchronizer`. Synchronizers are notified about some major events in a transaction's life. See `ISynchronizer` for details. """ def clearSynchs(): """Unregister all registered `ISynchronizer` objects. This exists to support test cleanup/initialization """ def registeredSynchs(): """Determine if any `ISynchronizers` are registered. Return true if any are registered, and return False otherwise. This exists to support test cleanup/initialization """ def attempts(number=3): """Generate up to *number* (transactional) context managers. This method is typically used as follows:: for attempt in transaction_manager.attempts(): with attempt: *with block* The ``with attempt:`` starts a new transaction for the execution of the *with block*. If the execution succeeds, the (then current) transaction is commited and the ``for`` loop terminates. If the execution raised an exception, then the transaction is aborted. If the exception was some kind of `retriable error <ITransaction.isRetryableError>` and the maximal number of attempts is not yet reached, then a next iteration of the ``for`` loop starts. In all other cases, the ``for`` loop terminates with the exception. """ def run(func=None, tries=3): """Call *func()* in its own transaction; retry in case of some kind of `retriable error <ITransaction.isRetryableError>`. The call is tried up to *tries* times. The call is performed in a new transaction. After the call, the (then current) transaction is committed (no exception) or aborted (exception). `run` supports the alternative signature ``run(tries=3)``. If *func* is not given or passed as `None`, then the call to `run` returns a function taking *func* as argument and then calling ``run(func, tries)``. """
[docs]class ITransaction(Interface): """Object representing a running transaction.""" user = Attribute( """A user name associated with the transaction. The format of the user name is defined by the application. The value is text (unicode). Storages record the user value, as meta-data, when a transaction commits. A storage may impose a limit on the size of the value; behavior is undefined if such a limit is exceeded (for example, a storage may raise an exception, or truncate the value). """) description = Attribute( """A textual description of the transaction. The value is text (unicode). Method `note` is the intended way to set the value. Storages record the description, as meta-data, when a transaction commits. A storage may impose a limit on the size of the description; behavior is undefined if such a limit is exceeded (for example, a storage may raise an exception, or truncate the value). """) extension = Attribute( "A dictionary containing application-defined metadata.") def commit(): """Finalize the transaction. This executes the two-phase commit algorithm for all `IDataManager` objects associated with the transaction. """ def abort(): """Abort the transaction. This is called from the application. This can only be called before the two-phase commit protocol has been started. """ def doom(): """Doom the transaction. Dooms the current transaction. This will cause `DoomedTransaction` to be raised on any attempt to commit the transaction. Otherwise the transaction will behave as if it was active. """ def savepoint(optimistic=False): """Create a savepoint. If the *optimistic* argument is true, then data managers that don't support savepoints can be used, but an error will be raised if the savepoint is rolled back. An `ISavepoint` object is returned. """ def join(datamanager): """Add a data manager to the transaction. *datamanager* must provide the `IDataManager` interface. """ def note(text): """Add text (unicode) to the transaction description. This modifies the `description` attribute; see its docs for more detail. First surrounding whitespace is stripped from *text*. If `description` is currently an empty string, then the stripped text becomes its value, else two newlines and the stripped text are appended to `description`. """ def setExtendedInfo(name, value): """Add extension data to the transaction. :param text name: is the text (unicode) name of the extension property to set :param value: must be picklable and json serializable Multiple calls may be made to set multiple extension properties, provided the names are distinct. Storages record the extension data, as meta-data, when a transaction commits. A storage may impose a limit on the size of extension data; behavior is undefined if such a limit is exceeded (for example, a storage may raise an exception, or remove `<name, value>` pairs). """ def addBeforeCommitHook(hook, args=(), kws=None): """Register a hook to call before the transaction is committed. The specified hook function will be called after the transaction's commit method has been called, but before the commit process has been started. :param sequence args: Additional positional arguments to be passed to the hook. The default is to pass no positional arguments. :param dict kws: Keyword arguments to pass to the hook. The default is to pass no keyword arguments. Multiple hooks can be registered and will be called in the order they were registered (first registered, first called). This method can also be called from a hook: an executing hook can register more hooks. Applications should take care to avoid creating infinite loops by recursively registering hooks. Hooks are called only for a top-level commit. A savepoint creation does not call any hooks. If the transaction is aborted, hooks are not called, and are discarded. Calling a hook "consumes" its registration too: hook registrations do not persist across transactions. If it's desired to call the same hook on every transaction commit, then `addBeforeCommitHook` must be called with that hook during every transaction; in such a case consider registering a synchronizer object via `ITransactionManager.registerSynch` instead. """ def getBeforeCommitHooks(): """Return iterable producing registered `addBeforeCommitHook` hooks. A triple ``(hook, args, kws)`` is produced for each registered hook. The hooks are produced in the order in which they would be invoked by a top-level transaction commit. """ def addAfterCommitHook(hook, args=(), kws=None): """Register a hook to call after a transaction commit attempt. The specified hook function will be called after the transaction commit succeeds or aborts. The first argument passed to the hook is a Boolean value, `True` if the commit succeeded, or `False` if the commit aborted. *args* and *kws* are interpreted as for `addBeforeCommitHook` (with the exception that there is always one positional argument, the commit status). As with `addBeforeCommitHook`, multiple hooks can be registered, savepoint creation doesn't call any hooks, and calling a hook consumes its registration. """ def getAfterCommitHooks(): """Return iterable producing the registered `addAfterCommitHook` hooks. As with `getBeforeCommitHooks`, a triple ``(hook, args, kws)`` is produced for each registered hook. The hooks are produced in the order in which they would be invoked by a top-level transaction commit. """ def addBeforeAbortHook(hook, args=(), kws=None): """Register a hook to call before the transaction is aborted. The specified hook function will be called after the transaction's abort method has been called, but before the abort process has been started. *args* and *kws* are interpreted as for `addBeforeCommitHook`. As with `addBeforeCommitHook`, multiple hooks can be registered, savepoint creation doesn't call any hooks, and calling a hook consumes its registration. Abort hooks are called only for a top-level abort. If the transaction is committed, abort hooks are not called. This is true even if the commit fails. In this case, however, the transaction is in the ``COMMITFAILED`` state and is virtually unusable; therefore, a top-level abort will typically follow. """ def getBeforeAbortHooks(): """Return iterable producing the registered `addBeforeAbortHook` hooks. As with `getBeforeCommitHooks`, a triple ``(hook, args, kws)`` is produced for each registered hook. The hooks are produced in the order in which they would be invoked by a top-level transaction abort. """ def addAfterAbortHook(hook, args=(), kws=None): """Register a hook to call after a transaction abort. The specified hook function will be called after the transaction abort. *args* and *kws* are interpreted as for `addBeforeCommitHook`. As with `addBeforeCommitHook`, multiple hooks can be registered, savepoint creation doesn't call any hooks, and calling a hook consumes its registration. As with `addBeforeAbortHook`, these hooks are called only for a top-level abort. See that method for more. """ def getAfterAbortHooks(): """Return iterable producing the registered `addAfterAbortHook` hooks. As with `getBeforeCommitHooks`, a triple ``(hook, args, kws)`` is produced for each registered hook. The hooks are produced in the order in which they would be invoked by a top-level transaction abort. """ def set_data(ob, data): """Hold *data* on behalf of an object For objects such as data managers or their subobjects that work with multiple transactions, it's convenient to store transaction-specific data on the transaction itself. The transaction knows nothing about the data, but simply holds it on behalf of the object. The object passed should be the object that needs the data, as opposed to a simple object like a string. (Internally, the id of the object is used as the key.) """ def data(ob): """Retrieve data held on behalf of an object. See `set_data`. """ def isRetryableError(error): """Determine if the error is retryable. Returns true if any joined `IRetryDataManager` considers the error transient *or* if the error is an instance of `TransientError`. Such errors may occur due to concurrency issues in the underlying storage engine. """
class IDataManager(Interface): """Objects that manage transactional storage. These objects may manage data for other objects, or they may manage non-object storages, such as relational databases. For example, a `ZODB.Connection.Connection`. Note that when some data is modified, that data's data manager should join a transaction so that data can be committed when the user commits the transaction. These objects implement the two-phase commit protocol in order to allow multiple data managers to safely participate in a single transaction. The methods `tpc_begin`, `commit`, `tpc_vote`, and then either `tpc_finish` or `tpc_abort` are normally called in that order when committing a transaction. """ transaction_manager = Attribute( """The transaction manager (TM) used by this data manager. This is a public attribute, intended for read-only use. The value is an instance of `ITransactionManager`, typically set by the data manager's constructor. """) def abort(transaction): """Abort a transaction and forget all changes. Abort must be called outside of a two-phase commit. Abort is called by the transaction manager to abort transactions that are not yet in a two-phase commit. It may also be called when rolling back a savepoint made before the data manager joined the transaction. In any case, after abort is called, the data manager is no longer participating in the transaction. If there are new changes, the data manager must rejoin the transaction. """ def tpc_begin(transaction): """Begin commit of a transaction, starting the two-phase commit. *transaction* is the `ITransaction` instance associated with the transaction being committed. """ def commit(transaction): """Commit modifications to registered objects. Save changes to be made persistent if the transaction commits (if `tpc_finish` is called later). If `tpc_abort` is called later, changes must not persist. This includes conflict detection and handling. If no conflicts or errors occur, the data manager should be prepared to make the changes persist when `tpc_finish` is called. """ def tpc_vote(transaction): """Verify that a data manager can commit the transaction. This is the last chance for a data manager to vote 'no'. A data manager votes 'no' by raising an exception. *transaction* is the `ITransaction` instance associated with the transaction being committed. """ def tpc_finish(transaction): """Indicate confirmation that the transaction is done. Make all changes to objects modified by this transaction persist. *transaction* is the `ITransaction` instance associated with the transaction being committed. This should never fail. If this raises an exception, the database is not expected to maintain consistency; it's a serious error. """ def tpc_abort(transaction): """Abort a transaction. This is called by a transaction manager to end a two-phase commit on the data manager. Abandon all changes to objects modified by this transaction. *transaction* is the `ITransaction` instance associated with the transaction being committed. This should never fail. """ def sortKey(): """Return a key to use for ordering registered `IDataManagers`. In order to guarantee a total ordering, keys **must** be `strings <str>`. Transactions use a global sort order to prevent deadlock when committing transactions involving multiple data managers. The data managers **must** define a `sortKey` method that provides a global ordering across all registered data managers. """ # Alternate version: # """Return a consistent sort key for this connection. # # This allows ordering multiple connections that use the same storage # in a consistent manner. This is unique for the lifetime of a # connection, which is good enough to avoid ZEO deadlocks. # """ class ISavepointDataManager(IDataManager): def savepoint(): """Return a data-manager savepoint (`IDataManagerSavepoint`).""" class IRetryDataManager(IDataManager): def should_retry(exception): """Return whether a given exception instance should be retried. A data manager can provide this method to indicate that a a transaction that raised the given error should be retried. This method may be called by an `ITransactionManager` when considering whether to retry a failed transaction. """ class IDataManagerSavepoint(Interface): """Savepoint for data-manager changes for use in transaction savepoints. Datamanager savepoints are used by, and only by, transaction savepoints. Note that data manager savepoints don't have any notion of, or responsibility for, validity. It isn't the responsibility of data-manager savepoints to prevent multiple rollbacks or rollbacks after transaction termination. Preventing invalid savepoint rollback is the responsibility of transaction rollbacks. Application code should never use data-manager savepoints. """ def rollback(): """Rollback any work done since the savepoint. """ class ISavepoint(Interface): """A transaction savepoint. """ def rollback(): """Rollback any work done since the savepoint. `InvalidSavepointRollbackError` is raised if the savepoint isn't valid. """ valid = Attribute( "Boolean indicating whether the savepoint is valid") class InvalidSavepointRollbackError(Exception): """Attempt to rollback an invalid savepoint. A savepoint may be invalid because: - The surrounding transaction has committed or aborted. - An earlier savepoint in the same transaction has been rolled back. """ class ISynchronizer(Interface): """Objects that participate in the transaction-boundary notification API. """ def beforeCompletion(transaction): """Hook that is called by the transaction at the start of a commit.""" def afterCompletion(transaction): """Hook that is called by the transaction after completing a commit.""" def newTransaction(transaction): """Hook that is called at the start of a transaction. This hook is called when, and only when, a transaction manager's `~ITransactionManager.begin` method is called explicitly. """ class TransactionError(Exception): """An error occurred due to normal transaction processing.""" class TransactionFailedError(TransactionError): """Cannot perform an operation on a transaction that previously failed. An attempt was made to commit a transaction, or to join a transaction, but this transaction previously raised an exception during an attempt to commit it. The transaction must be explicitly aborted by invoking `ITransaction.abort`. (If the transaction manager is not operating in explicit mode, then `ITransactionManager.begin` can also be used to perform an implicit abort.) """ class DoomedTransaction(TransactionError): """A commit was attempted on a transaction that was doomed.""" class TransientError(TransactionError): """An error has occured when performing a transaction. It's possible that retrying the transaction will succeed. """ class NoTransaction(TransactionError): """No transaction has been defined An application called an operation on a transaction manager that affects an exciting transaction, but no transaction was begun. The transaction manager was in explicit mode, so a new transaction was not explicitly created. .. versionadded:: 2.1.0 """ class AlreadyInTransaction(TransactionError): """Attempt to create a new transaction without ending a preceding one An application called `~ITransactionManager.begin` on a transaction manager in explicit mode, without committing or aborting the previous transaction. .. versionadded:: 2.1.0 """