db/manager: Drop async method

As far as I can tell using a separate process doesn't actually improve
performance, it makes it worse. The work that we're passing off to the
separate function isn't necessarily work that's well suited to being
handed off, there isn't a lot of computation and the objects that need
to be passed across the pipe are fairly large (at least when considering
a pipe). Converting the function to a generator gives better performance
and simplifies the implementation.

4 files changed, 30 insertions, 158 deletions

diff --git a/alot/buffers/search.py b/alot/buffers/search.py
index 203ef483..d64e857f 100644
--- a/alot/buffers/search.py
+++ b/alot/buffers/search.py
@@ -6,7 +6,7 @@ from notmuch import NotmuchError
 
 from .buffer import Buffer
 from ..settings.const import settings
-from ..walker import PipeWalker
+from ..walker import IterableWalker
 from ..widgets.search import ThreadlineWidget
 
 
@@ -26,7 +26,6 @@ class SearchBuffer(Buffer):
         self.sort_order = sort_order or default_order
         self.result_count = 0
         self.isinitialized = False
-        self.proc = None  # process that fills our pipe
         self.rebuild()
         Buffer.__init__(self, ui, self.body)
 
@@ -42,22 +41,9 @@ class SearchBuffer(Buffer):
         info['result_count_positive'] = 's' if self.result_count > 1 else ''
         return info
 
-    def cleanup(self):
-        self.kill_filler_process()
-
-    def kill_filler_process(self):
-        """
-        terminates the process that fills this buffers
-        :class:`~alot.walker.PipeWalker`.
-        """
-        if self.proc:
-            if self.proc.is_alive():
-                self.proc.terminate()
-
     def rebuild(self, reverse=False):
         self.isinitialized = True
         self.reversed = reverse
-        self.kill_filler_process()
 
         if reverse:
             order = self._REVERSE[self.sort_order]
@@ -70,9 +56,8 @@ class SearchBuffer(Buffer):
 
         try:
             self.result_count = self.dbman.count_messages(self.querystring)
-            self.pipe, self.proc = self.dbman.get_threads(self.querystring,
-                                                          order,
-                                                          exclude_tags)
+            threads = self.dbman.get_threads(
+                self.querystring, order, exclude_tags)
         except NotmuchError:
             self.ui.notify('malformed query string: %s' % self.querystring,
                            'error')
@@ -80,9 +65,9 @@ class SearchBuffer(Buffer):
             self.body = self.listbox
             return
 
-        self.threadlist = PipeWalker(self.pipe, ThreadlineWidget,
-                                     dbman=self.dbman,
-                                     reverse=reverse)
+        self.threadlist = IterableWalker(threads, ThreadlineWidget,
+                                         dbman=self.dbman,
+                                         reverse=reverse)
 
         self.listbox = urwid.ListBox(self.threadlist)
         self.body = self.listbox
diff --git a/alot/db/manager.py b/alot/db/manager.py
index 956ddcbc..af42a1f5 100644
--- a/alot/db/manager.py
+++ b/alot/db/manager.py
@@ -1,14 +1,10 @@
 # Copyright (C) 2011-2012  Patrick Totzke <patricktotzke@gmail.com>
+# Copyright © Dylan Baker
 # This file is released under the GNU GPL, version 3 or a later revision.
 # For further details see the COPYING file
 from collections import deque
-import errno
+import asyncio
 import logging
-import multiprocessing
-import os
-import signal
-import sys
-import threading
 
 from notmuch import Database, NotmuchError, XapianError
 import notmuch
@@ -23,47 +19,6 @@ from .utils import is_subdir_of
 from ..settings.const import settings
 
 
-class FillPipeProcess(multiprocessing.Process):
-
-    def __init__(self, it, stdout, stderr, pipe, fun=(lambda x: x)):
-        multiprocessing.Process.__init__(self)
-        self.it = it
-        self.pipe = pipe[1]
-        self.fun = fun
-        self.keep_going = True
-        self.stdout = stdout
-        self.stderr = stderr
-
-    def handle_sigterm(self, signo, frame):
-        # this is used to suppress any EINTR errors at interpreter
-        # shutdown
-        self.keep_going = False
-
-        # raises SystemExit to shut down the interpreter from the
-        # signal handler
-        sys.exit()
-
-    def run(self):
-        # replace filedescriptors 1 and 2 (stdout and stderr) with
-        # pipes to the parent process
-        os.dup2(self.stdout, 1)
-        os.dup2(self.stderr, 2)
-
-        # register a signal handler for SIGTERM
-        signal.signal(signal.SIGTERM, self.handle_sigterm)
-
-        for a in self.it:
-            try:
-                self.pipe.send(self.fun(a))
-            except IOError as e:
-                # suppress spurious EINTR errors at interpreter
-                # shutdown
-                if e.errno != errno.EINTR or self.keep_going:
-                    raise
-
-        self.pipe.close()
-
-
 class DBManager:
     """
     Keeps track of your index parameters, maintains a write-queue and
@@ -198,15 +153,6 @@ class DBManager:
                     raise e
                 logging.debug('flush finished')
 
-    def kill_search_processes(self):
-        """
-        terminate all search processes that originate from
-        this managers :meth:`get_threads`.
-        """
-        for p in self.processes:
-            p.terminate()
-        self.processes = []
-
     def tag(self, querystring, tags, afterwards=None, remove_rest=False):
         """
         add tags to messages matching `querystring`.
@@ -309,75 +255,6 @@ class DBManager:
         db = Database(path=self.path)
         return {k[6:]: v for k, v in db.get_configs('query.')}
 
-    def async_(self, cbl, fun):
-        """
-        return a pair (pipe, process) so that the process writes
-        `fun(a)` to the pipe for each element `a` in the iterable returned
-        by the callable `cbl`.
-
-        :param cbl: a function returning something iterable
-        :type cbl: callable
-        :param fun: an unary translation function
-        :type fun: callable
-        :rtype: (:class:`multiprocessing.Pipe`,
-                :class:`multiprocessing.Process`)
-        """
-        # create two unix pipes to redirect the workers stdout and
-        # stderr
-        stdout = os.pipe()
-        stderr = os.pipe()
-
-        # create a multiprocessing pipe for the results
-        pipe = multiprocessing.Pipe(False)
-        receiver, sender = pipe
-
-        process = FillPipeProcess(cbl(), stdout[1], stderr[1], pipe, fun)
-        process.start()
-        self.processes.append(process)
-        logging.debug('Worker process %s spawned', process.pid)
-
-        def threaded_wait():
-            # wait(2) for the process to die
-            process.join()
-
-            if process.exitcode < 0:
-                msg = 'received signal {0}'.format(-process.exitcode)
-            elif process.exitcode > 0:
-                msg = 'returned error code {0}'.format(process.exitcode)
-            else:
-                msg = 'exited successfully'
-
-            logging.debug('Worker process %s %s', process.pid, msg)
-            self.processes.remove(process)
-
-        # XXX: it would be much nicer to run this as a coroutine than a thread,
-        # except that this code is executed before the eventloop is started.
-        #
-        # spawn a thread to collect the worker process once it dies
-        # preventing it from hanging around as zombie
-        threading.Thread(target=threaded_wait).start()
-
-        # TODO: avoid this if logging level > debug
-        def threaded_reader(prefix, fd):
-            with os.fdopen(fd) as handle:
-                for line in handle:
-                    logging.debug('Worker process %s said on %s: %s',
-                                  process.pid, prefix, line.rstrip())
-
-        # spawn two threads that read from the stdout and stderr pipes
-        # and write anything that appears there to the log
-        threading.Thread(target=threaded_reader,
-                         args=('stdout', stdout[0])).start()
-        os.close(stdout[1])
-        threading.Thread(target=threaded_reader,
-                         args=('stderr', stderr[0])).start()
-        os.close(stderr[1])
-
-        # closing the sending end in this (receiving) process guarantees
-        # that here the appropriate EOFError is raised upon .recv in the walker
-        sender.close()
-        return receiver, process
-
     def get_threads(self, querystring, sort='newest_first', exclude_tags=None):
         """
         asynchronously look up thread ids matching `querystring`.
@@ -401,7 +278,8 @@ class DBManager:
         if exclude_tags:
             for tag in exclude_tags:
                 q.exclude_tag(tag)
-        return self.async_(q.search_threads, (lambda a: a.get_thread_id()))
+        for t in q.search_threads():
+            yield t.get_thread_id()
 
     def query(self, querystring):
         """
diff --git a/alot/walker.py b/alot/walker.py
index e4264103..cfefc9e6 100644
--- a/alot/walker.py
+++ b/alot/walker.py
@@ -1,20 +1,30 @@
 # Copyright (C) 2011-2012  Patrick Totzke <patricktotzke@gmail.com>
+# Copyright © 2018 Dylan Baker
 # This file is released under the GNU GPL, version 3 or a later revision.
 # For further details see the COPYING file
 import logging
 import urwid
 
 
-class PipeWalker(urwid.ListWalker):
-    """urwid.ListWalker that reads next items from a pipe and wraps them in
-    `containerclass` widgets for displaying
+class IterableWalker(urwid.ListWalker):
 
-    Attributes that should be considered publicly readable:
-        :attr lines: the lines obtained from the pipe
-        :type lines: list(`containerclass`)
+    """An urwid walker for iterables.
+
+    Works like ListWalker, except it takes an iterable object instead of a
+    concrete type. This allows for lazy operations of very large sequences of
+    data, such as a sequences of threads with certain notmuch tags.
+
+    :param iterable: An iterator of objects to walk over
+    :type iterable: Iterable[T]
+    :param containerclass: An urwid widget to wrap each object in
+    :type containerclass: urwid.Widget
+    :param reverse: Reverse the order of the iterable
+    :type reverse: bool
+    :param **kwargs: Forwarded to container class.
     """
-    def __init__(self, pipe, containerclass, reverse=False, **kwargs):
-        self.pipe = pipe
+
+    def __init__(self, iterable, containerclass, reverse=False, **kwargs):
+        self.iterable = iterable
         self.kwargs = kwargs
         self.containerclass = containerclass
         self.lines = []
@@ -71,10 +81,10 @@ class PipeWalker(urwid.ListWalker):
         try:
             # the next line blocks until it can read from the pipe or
             # EOFError is raised. No races here.
-            next_obj = self.pipe.recv()
+            next_obj = next(self.iterable)
             next_widget = self.containerclass(next_obj, **self.kwargs)
             self.lines.append(next_widget)
-        except EOFError:
+        except StopIteration:
             logging.debug('EMPTY PIPE')
             next_widget = None
             self.empty = True
diff --git a/tests/db/test_manager.py b/tests/db/test_manager.py
index e675aed4..f7a47a58 100644
--- a/tests/db/test_manager.py
+++ b/tests/db/test_manager.py
@@ -37,7 +37,6 @@ class TestDBManager(utilities.TestCaseClassCleanup):
         cls.manager = DBManager(cls.dbpath)
 
         # clean up temporary database
-        cls.addClassCleanup(cls.manager.kill_search_processes)
         cls.addClassCleanup(shutil.rmtree, cls.dbpath)
 
         # let global settings manager read our temporary notmuch config