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Add context manager for unpinning #57

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Add context manager for unpinning #57

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1ce1974
Add support for nested context manager use
bardiharborow Jun 28, 2022
b40d9aa
Add context manager for unpinning
bardiharborow Jun 28, 2022
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27 changes: 22 additions & 5 deletions multidb/pinning.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@


__all__ = ['this_thread_is_pinned', 'pin_this_thread', 'unpin_this_thread',
'use_primary_db', 'use_master', 'db_write']
'use_primary_db', 'use_secondary_db', 'use_master', 'db_write']


_locals = threading.local()
Expand All @@ -33,8 +33,8 @@ def unpin_this_thread():
_locals.pinned = False


class UsePrimaryDB(object):
"""A contextmanager/decorator to use the primary database."""
class _UseDB(object):
"""A contextmanager/decorator to use the specified database."""
def __call__(self, func):
@wraps(func)
def decorator(*args, **kw):
Expand All @@ -45,13 +45,29 @@ def decorator(*args, **kw):
def __enter__(self):
_locals.old = getattr(_locals, 'old', [])
_locals.old.append(this_thread_is_pinned())
pin_this_thread()

def __exit__(self, type, value, tb):
if not _locals.old.pop():
previous_state = _locals.old.pop()
if previous_state:
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ℹ️ This introduces a subtle behaviour change. Previously, manual use of unpin_this_thread() would leak out of the context block, for example when:

  1. a thread is pinned
  2. enters the context block (_locals.old = True)
  3. is manually unpinned (with unpin_this_thread())
  4. exits the context block (not _locals.old == False so no action is taken)
  5. the thread will be unpinned when it reaches here

This new code will always restore the previous pinning state when exiting a context block. In my view this is more predictable, but I'm open to your opinion on this.

pin_this_thread()
else:
unpin_this_thread()


class UsePrimaryDB(_UseDB):
"""A contextmanager/decorator to use the primary database."""
def __enter__(self):
super(UsePrimaryDB, self).__enter__()
pin_this_thread()


class UseSecondaryDB(_UseDB):
"""A contextmanager/decorator to use the secondary database."""
def __enter__(self):
super(UseSecondaryDB, self).__enter__()
unpin_this_thread()


class DeprecatedUseMaster(UsePrimaryDB):
def __enter__(self):
warnings.warn(
Expand All @@ -63,6 +79,7 @@ def __enter__(self):


use_primary_db = UsePrimaryDB()
use_secondary_db = UseSecondaryDB()
use_master = DeprecatedUseMaster()


Expand Down
250 changes: 249 additions & 1 deletion multidb/tests.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,8 @@
pinning_cookie_samesite, pinning_cookie_secure,
pinning_seconds, PinningRouterMiddleware)
from multidb.pinning import (this_thread_is_pinned, pin_this_thread,
unpin_this_thread, use_primary_db, db_write)
unpin_this_thread, use_primary_db,
use_secondary_db, db_write)


class UnpinningTestCase(TestCase):
Expand Down Expand Up @@ -218,6 +219,22 @@ def check_outer():
check_outer()
assert not this_thread_is_pinned()

def test_decorator_nested_mixed(self):
@use_primary_db
def check_inner():
assert this_thread_is_pinned()

@use_secondary_db
def check_outer():
assert not this_thread_is_pinned()
check_inner()
assert not this_thread_is_pinned()

unpin_this_thread()
assert not this_thread_is_pinned()
check_outer()
assert not this_thread_is_pinned()

def test_decorator_resets(self):
@use_primary_db
def check():
Expand All @@ -243,6 +260,22 @@ def check_outer():
check_outer()
assert this_thread_is_pinned()

def test_decorator_resets_nested_mixed(self):
@use_primary_db
def check_inner():
assert this_thread_is_pinned()

@use_secondary_db
def check_outer():
assert not this_thread_is_pinned()
check_inner()
assert not this_thread_is_pinned()

pin_this_thread()
assert this_thread_is_pinned()
check_outer()
assert this_thread_is_pinned()

def test_context_manager(self):
unpin_this_thread()
assert not this_thread_is_pinned()
Expand All @@ -260,6 +293,16 @@ def test_context_manager_nested(self):
assert this_thread_is_pinned()
assert not this_thread_is_pinned()

def test_context_manager_nested_mixed(self):
unpin_this_thread()
assert not this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
with use_primary_db:
assert this_thread_is_pinned()
assert not this_thread_is_pinned()
assert not this_thread_is_pinned()

def test_context_manager_resets(self):
pin_this_thread()
assert this_thread_is_pinned()
Expand All @@ -277,6 +320,16 @@ def test_context_manager_resets_nested(self):
assert this_thread_is_pinned()
assert this_thread_is_pinned()

def test_context_manager_resets_nested_mixed(self):
pin_this_thread()
assert this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
with use_primary_db:
assert this_thread_is_pinned()
assert not this_thread_is_pinned()
assert this_thread_is_pinned()

def test_context_manager_exception(self):
unpin_this_thread()
assert not this_thread_is_pinned()
Expand Down Expand Up @@ -334,6 +387,201 @@ def thread2_worker():
self.assertEqual(pinned[1], False)


class UseSecondaryDBTests(TestCase):
def test_decorator(self):
@use_secondary_db
def check():
assert not this_thread_is_pinned()
pin_this_thread()
assert this_thread_is_pinned()
check()
assert this_thread_is_pinned()

def test_decorator_nested(self):
@use_secondary_db
def check_inner():
assert not this_thread_is_pinned()

@use_secondary_db
def check_outer():
assert not this_thread_is_pinned()
check_inner()
assert not this_thread_is_pinned()

pin_this_thread()
assert this_thread_is_pinned()
check_outer()
assert this_thread_is_pinned()

def test_decorator_nested_mixed(self):
@use_secondary_db
def check_inner():
assert not this_thread_is_pinned()

@use_primary_db
def check_outer():
assert this_thread_is_pinned()
check_inner()
assert this_thread_is_pinned()

pin_this_thread()
assert this_thread_is_pinned()
check_outer()
assert this_thread_is_pinned()

def test_decorator_resets(self):
@use_secondary_db
def check():
assert not this_thread_is_pinned()
unpin_this_thread()
assert not this_thread_is_pinned()
check()
assert not this_thread_is_pinned()

def test_decorator_resets_nested(self):
@use_secondary_db
def check_inner():
assert not this_thread_is_pinned()

@use_secondary_db
def check_outer():
assert not this_thread_is_pinned()
check_inner()
assert not this_thread_is_pinned()

unpin_this_thread()
assert not this_thread_is_pinned()
check_outer()
assert not this_thread_is_pinned()

def test_decorator_resets_nested_mixed(self):
@use_secondary_db
def check_inner():
assert not this_thread_is_pinned()

@use_primary_db
def check_outer():
assert this_thread_is_pinned()
check_inner()
assert this_thread_is_pinned()

unpin_this_thread()
assert not this_thread_is_pinned()
check_outer()
assert not this_thread_is_pinned()

def test_context_manager(self):
pin_this_thread()
assert this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert this_thread_is_pinned()

def test_context_manager_nested(self):
pin_this_thread()
assert this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert not this_thread_is_pinned()
assert this_thread_is_pinned()

def test_context_manager_nested_mixed(self):
pin_this_thread()
assert this_thread_is_pinned()
with use_primary_db:
assert this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert this_thread_is_pinned()
assert this_thread_is_pinned()

def test_context_manager_resets(self):
unpin_this_thread()
assert not this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert not this_thread_is_pinned()

def test_context_manager_resets_nested(self):
unpin_this_thread()
assert not this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert not this_thread_is_pinned()
assert not this_thread_is_pinned()

def test_context_manager_resets_nested_mixed(self):
unpin_this_thread()
assert not this_thread_is_pinned()
with use_primary_db:
assert this_thread_is_pinned()
with use_secondary_db:
assert not this_thread_is_pinned()
assert this_thread_is_pinned()
assert not this_thread_is_pinned()

def test_context_manager_exception(self):
pin_this_thread()
assert this_thread_is_pinned()
with self.assertRaises(ValueError):
with use_secondary_db:
assert not this_thread_is_pinned()
raise ValueError
assert this_thread_is_pinned()

def test_multithreaded_unpinning(self):
thread1_lock = Lock()
thread2_lock = Lock()
thread1_lock.acquire()
thread2_lock.acquire()
orchestrator = Lock()
orchestrator.acquire()

pinned = {}

def thread1_worker():
pin_this_thread()
with use_secondary_db:
orchestrator.release()
thread1_lock.acquire()

pinned[1] = this_thread_is_pinned()

def thread2_worker():
unpin_this_thread()
with use_secondary_db:
orchestrator.release()
thread2_lock.acquire()

pinned[2] = this_thread_is_pinned()
orchestrator.release()

thread1 = Thread(target=thread1_worker)
thread2 = Thread(target=thread2_worker)

# thread1 starts, entering `use_primary_db` from a pinned state
thread1.start()
orchestrator.acquire()

# thread2 starts, entering `use_primary_db` from an unpinned state
thread2.start()
orchestrator.acquire()

# thread2 finishes, returning to an unpinned state
thread2_lock.release()
thread2.join()
self.assertEqual(pinned[2], False)

# thread1 finishes, returning to a pinned state
thread1_lock.release()
thread1.join()
self.assertEqual(pinned[1], True)


class DeprecationTestCase(TestCase):
def test_masterslaverouter(self):
with warnings.catch_warnings(record=True) as w:
Expand Down