From 20af3ceffb47392e271611473fdbf19cb8397902 Mon Sep 17 00:00:00 2001
From: Joshua Harlow <harlowja@gmail.com>
Date: Tue, 16 Jun 2015 23:50:36 -0700
Subject: [PATCH] Add and use a small retry helper utility object

---
 fasteners/_utils.py       | 30 +++++++++++++++++++
 fasteners/process_lock.py | 62 +++++++++++++--------------------------
 2 files changed, 50 insertions(+), 42 deletions(-)

diff --git a/fasteners/_utils.py b/fasteners/_utils.py
index 108b156..272e84b 100644
--- a/fasteners/_utils.py
+++ b/fasteners/_utils.py
@@ -17,6 +17,7 @@
 #    under the License.
 
 import logging
+import time
 
 from monotonic import monotonic as now  # noqa
 
@@ -59,6 +60,35 @@ class LockStack(object):
             am_left -= 1
 
 
+class RetryAgain(Exception):
+    """Exception to signal to retry helper to try again."""
+
+
+class Retry(object):
+    """A little retry helper object."""
+
+    def __init__(self, delay, max_delay,
+                 sleep_func=time.sleep):
+        self.delay = delay,
+        self.attempts = 0
+        self.max_delay = max_delay
+        self.sleep_func = sleep_func
+
+    def __call__(self, fn, *args, **kwargs):
+        while True:
+            self.attempts += 1
+            try:
+                return fn(*args, **kwargs)
+            except RetryAgain:
+                maybe_delay = self.attempts * self.delay
+                if maybe_delay < self.max_delay:
+                    actual_delay = maybe_delay
+                else:
+                    actual_delay = self.max_delay
+                actual_delay = max(0.0, actual_delay)
+                self.sleep_func(actual_delay)
+
+
 class StopWatch(object):
     """A really basic stop watch."""
 
diff --git a/fasteners/process_lock.py b/fasteners/process_lock.py
index cecfd00..d165304 100644
--- a/fasteners/process_lock.py
+++ b/fasteners/process_lock.py
@@ -16,8 +16,6 @@
 #    under the License.
 
 import errno
-import functools
-import itertools
 import logging
 import os
 import threading
@@ -30,10 +28,6 @@ from fasteners import _utils
 LOG = logging.getLogger(__name__)
 
 
-def _noop_delay(attempts):
-    return None
-
-
 def _ensure_tree(path):
     """Create a directory (and any ancestor directories required).
 
@@ -92,28 +86,25 @@ class _InterProcessLock(object):
         self.acquired = False
         self.sleep_func = sleep_func
 
-    def _do_acquire(self, delay_func, blocking, watch):
-        attempts_iter = itertools.count(1)
-        while True:
-            attempts = six.next(attempts_iter)
-            try:
-                self.trylock()
-            except IOError as e:
-                if e.errno in (errno.EACCES, errno.EAGAIN):
-                    if not blocking or watch.expired():
-                        return (False, attempts)
-                    else:
-                        delay_func(attempts)
+    def _try_acquire(self, blocking, watch):
+        try:
+            self.trylock()
+        except IOError as e:
+            if e.errno in (errno.EACCES, errno.EAGAIN):
+                if not blocking or watch.expired():
+                    return False
                 else:
-                    raise threading.ThreadError("Unable to acquire lock on"
-                                                " `%(path)s` due to"
-                                                " %(exception)s" %
-                                                {
-                                                    'path': self.path,
-                                                    'exception': e,
-                                                })
+                    raise _utils.RetryAgain()
             else:
-                return (True, attempts)
+                raise threading.ThreadError("Unable to acquire lock on"
+                                            " `%(path)s` due to"
+                                            " %(exception)s" %
+                                            {
+                                                'path': self.path,
+                                                'exception': e,
+                                            })
+        else:
+            return True
 
     def _do_open(self):
         basedir = os.path.dirname(self.path)
@@ -127,15 +118,6 @@ class _InterProcessLock(object):
         if self.lockfile is None or self.lockfile.closed:
             self.lockfile = open(self.path, 'a')
 
-    def _backoff_multiplier_delay(self, attempts, delay, max_delay):
-        maybe_delay = attempts * delay
-        if maybe_delay < max_delay:
-            actual_delay = maybe_delay
-        else:
-            actual_delay = max_delay
-        actual_delay = max(0.0, actual_delay)
-        self.sleep_func(actual_delay)
-
     def acquire(self, blocking=True,
                 delay=DELAY_INCREMENT, max_delay=MAX_DELAY,
                 timeout=None):
@@ -164,13 +146,9 @@ class _InterProcessLock(object):
             max_delay = delay
         self._do_open()
         watch = _utils.StopWatch(duration=timeout)
-        if blocking:
-            delay_func = functools.partial(self._backoff_multiplier_delay,
-                                           delay=delay, max_delay=max_delay)
-        else:
-            delay_func = _noop_delay
+        r = _utils.Retry(delay, max_delay, sleep_func=self.sleep_func)
         with watch:
-            gotten, attempts = self._do_acquire(delay_func, blocking, watch)
+            gotten = r(self._try_acquire, blocking, watch)
         if not gotten:
             self.acquired = False
             return False
@@ -179,7 +157,7 @@ class _InterProcessLock(object):
             LOG.log(_utils.BLATHER,
                     "Acquired file lock `%s` after waiting %0.3fs [%s"
                     " attempts were required]", self.path, watch.elapsed(),
-                    attempts)
+                    r.attempts)
             return True
 
     def _do_close(self):