Signed-off-by: Yiheng Wang [email protected]

Fixes #3962 .

Description

In this PR, the default value of num_workers is set to 1 for CacheDataset and all its subclasses. Some of the subclasses use the value 0, although it will be replaced by 1 automatically, zero thread is meaningless and it is actually an illegal input for multiprocessing.pool.ThreadPool (used within the CacheDataset, the source code of it is in here) thus I also modified them.
In addition, this PR also fixes a few typos and unify the docstrings for same arguments in different classes.

Status

Ready

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.