# Source code for fsspec.transaction

    from collections import deque

    class Transaction:
        """Filesystem transaction write context

        Gathers files for deferred commit or discard, so that several write
        operations can be finalized semi-atomically. This works by having this
        instance as the ``.transaction`` attribute of the given filesystem
        """

        def __init__(self, fs, **kwargs):
            """
            Parameters
            ----------
            fs: FileSystem instance
            """
            self.fs = fs
            self.files = deque()

        def __enter__(self):
            self.start()
            return self

        def __exit__(self, exc_type, exc_val, exc_tb):
            """End transaction and commit, if exit is not due to exception"""
            # only commit if there was no exception
            self.complete(commit=exc_type is None)
            if self.fs:
                self.fs._intrans = False
                self.fs._transaction = None
                self.fs = None

        def start(self):
            """Start a transaction on this FileSystem"""
            self.files = deque()  # clean up after previous failed completions
            self.fs._intrans = True

        def complete(self, commit=True):
            """Finish transaction: commit or discard all deferred files"""
            while self.files:
                f = self.files.popleft()
                if commit:
                    f.commit()
                else:
                    f.discard()
            self.fs._intrans = False
            self.fs._transaction = None
            self.fs = None

    class FileActor:
        def __init__(self):
            self.files = []

        def commit(self):
            for f in self.files:
                f.commit()
            self.files.clear()

        def discard(self):
            for f in self.files:
                f.discard()
            self.files.clear()

        def append(self, f):
            self.files.append(f)

    class DaskTransaction(Transaction):
        def __init__(self, fs):
            """
            Parameters
            ----------
            fs: FileSystem instance
            """
            import distributed

            super().__init__(fs)
            client = distributed.default_client()
            self.files = client.submit(FileActor, actor=True).result()

        def complete(self, commit=True):
            """Finish transaction: commit or discard all deferred files"""
            if commit:
                self.files.commit().result()
            else:
                self.files.discard().result()
            self.fs._intrans = False
            self.fs = None