[AryanRG]

Constructing a SoftReadWriteLock subclass on a path already used by the base class or a sibling can return the other class's cached object. This skips the requested subclass's initializer and overrides:

from filelock import SoftReadWriteLock

class CustomLock(SoftReadWriteLock):
    pass

base = SoftReadWriteLock("work.lock")
custom = CustomLock("work.lock")
assert type(custom) is CustomLock  # fails before this change

Give each concrete class its own weak singleton cache, reentrant mutex, and construction guard. Reset that state after fork and forward cooperative class-definition keywords. Same-class singleton reuse and recursive-construction rejection are preserved; separate classes still contend on the same underlying lock path.

Regression coverage includes all three construction orders, overlapping constructors across base/sibling/descendant classes, cooperative mixins, recursion and retry, concurrent same-class reuse, and child-process resets while another thread is constructing a subclass. The original three-order regression fails against the unchanged base.

Validation on macOS arm64:

• Python 3.15 full suite, old-client compatibility enabled: 2,413 passed, 63 skipped; 100% line and branch coverage.
• Python 3.11 sync/fork suites: 166 passed, 6 skipped.
• Hooks for the changed files, type checking, and whitespace checks passed.

The full tox matrix and other operating systems/runtimes have not been run locally; hosted checks remain separate validation.

AI tools assisted with implementation, testing, and review.