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common.py
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# Copyright (C) 2015-2019 The Software Heritage developers
# See the AUTHORS file at the top-level directory of this distribution
# License: GNU General Public License version 3, or any later version
# See top-level LICENSE file for more information
import inspect
import functools
def remove_kwargs(names):
def decorator(f):
sig = inspect.signature(f)
params = sig.parameters
params = [param for param in params.values()
if param.name not in names]
sig = sig.replace(parameters=params)
f.__signature__ = sig
return f
return decorator
def apply_options(cursor, options):
"""Applies the given postgresql client options to the given cursor.
Returns a dictionary with the old values if they changed."""
old_options = {}
for option, value in options.items():
cursor.execute('SHOW %s' % option)
old_value = cursor.fetchall()[0][0]
if old_value != value:
cursor.execute('SET LOCAL %s TO %%s' % option, (value,))
old_options[option] = old_value
return old_options
def db_transaction(**client_options):
"""decorator to execute Backend methods within DB transactions
The decorated method must accept a `cur` and `db` keyword argument
Client options are passed as `set` options to the postgresql server
"""
def decorator(meth, __client_options=client_options):
if inspect.isgeneratorfunction(meth):
raise ValueError(
'Use db_transaction_generator for generator functions.')
@remove_kwargs(['cur', 'db'])
@functools.wraps(meth)
def _meth(self, *args, **kwargs):
if 'cur' in kwargs and kwargs['cur']:
cur = kwargs['cur']
old_options = apply_options(cur, __client_options)
ret = meth(self, *args, **kwargs)
apply_options(cur, old_options)
return ret
else:
db = self.get_db()
try:
with db.transaction() as cur:
apply_options(cur, __client_options)
return meth(self, *args, db=db, cur=cur, **kwargs)
finally:
self.put_db(db)
return _meth
return decorator
def db_transaction_generator(**client_options):
"""decorator to execute Backend methods within DB transactions, while
returning a generator
The decorated method must accept a `cur` and `db` keyword argument
Client options are passed as `set` options to the postgresql server
"""
def decorator(meth, __client_options=client_options):
if not inspect.isgeneratorfunction(meth):
raise ValueError(
'Use db_transaction for non-generator functions.')
@remove_kwargs(['cur', 'db'])
@functools.wraps(meth)
def _meth(self, *args, **kwargs):
if 'cur' in kwargs and kwargs['cur']:
cur = kwargs['cur']
old_options = apply_options(cur, __client_options)
yield from meth(self, *args, **kwargs)
apply_options(cur, old_options)
else:
db = self.get_db()
try:
with db.transaction() as cur:
apply_options(cur, __client_options)
yield from meth(self, *args, db=db, cur=cur, **kwargs)
finally:
self.put_db(db)
return _meth
return decorator

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