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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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30 changes: 24 additions & 6 deletions multidb/pinning.py
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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 master database."""
class _UseDB(object):
"""A contextmanager/decorator to use the specified database."""
def __call__(self, func):
@wraps(func)
def decorator(*args, **kw):
Expand All @@ -43,14 +43,31 @@ def decorator(*args, **kw):
return decorator

def __enter__(self):
_locals.old = this_thread_is_pinned()
pin_this_thread()
_locals.old = getattr(_locals, 'old', [])
_locals.old.append(this_thread_is_pinned())

def __exit__(self, type, value, tb):
if not _locals.old:
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 @@ -62,6 +79,7 @@ def __enter__(self):


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


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