# Buggy code
def run(self, iterator, play_context):
    """
    The linear strategy is simple - get the next task and queue
    it for all hosts, then wait for the queue to drain before
    moving on to the next task
    """

    # iteratate over each task, while there is one left to run
    result = self._tqm.RUN_OK
    work_to_do = True
    while work_to_do and not self._tqm._terminated:
        try:
            display.debug("getting the remaining hosts for this loop")
            hosts_left = [
                host
                for host in self._inventory.get_hosts(iterator._play.hosts)
                if host.name not in self._tqm._unreachable_hosts
            ]
            display.debug("done getting the remaining hosts for this loop")

            # queue up this task for each host in the inventory
            callback_sent = False
            work_to_do = False

            host_results = []
            host_tasks = self._get_next_task_lockstep(hosts_left, iterator)

            # skip control
            skip_rest = False
            choose_step = True

            # flag set if task is set to any_errors_fatal
            any_errors_fatal = False

            results = []
            for host, task in host_tasks:
                if not task:
                    continue

                if self._tqm._terminated:
                    break

                run_once = False
                work_to_do = True

                # test to see if the task across all hosts points to an action plugin which
                # sets BYPASS_HOST_LOOP to true, or if it has run_once enabled. If so, we
                # will only send this task to the first host in the list.

                try:
                    action = action_loader.get(task.action, class_only=True)
                except KeyError:
                    # we don't care here, because the action may simply not have a
                    # corresponding action plugin
                    action = None

                # check to see if this task should be skipped, due to it being a member of a
                # role which has already run (and whether that role allows duplicate execution)
                if task._role and task._role.has_run(host):
                    # If there is no metadata, the default behavior is to not allow duplicates,
                    # if there is metadata, check to see if the allow_duplicates flag was set to true
                    if (
                        task._role._metadata is None
                        or task._role._metadata
                        and not task._role._metadata.allow_duplicates
                    ):
                        display.debug(
                            "'%s' skipped because role has already run" % task
                        )
                        continue

                if task.action == "meta":
                    # for the linear strategy, we run meta tasks just once and for
                    # all hosts currently being iterated over rather than one host
                    results.extend(
                        self._execute_meta(task, play_context, iterator, host)
                    )
                    if task.args.get("_raw_params", None) != "noop":
                        run_once = True
                else:
                    # handle step if needed, skip meta actions as they are used internally
                    if self._step and choose_step:
                        if self._take_step(task):
                            choose_step = False
                        else:
                            skip_rest = True
                            break

                    display.debug("getting variables")
                    task_vars = self._variable_manager.get_vars(
                        loader=self._loader, play=iterator._play, host=host, task=task
                    )
                    self.add_tqm_variables(task_vars, play=iterator._play)
                    templar = Templar(loader=self._loader, variables=task_vars)
                    display.debug("done getting variables")

                    run_once = (
                        templar.template(task.run_once)
                        or action
                        and getattr(action, "BYPASS_HOST_LOOP", False)
                    )

                    if (task.any_errors_fatal or run_once) and not task.ignore_errors:
                        any_errors_fatal = True

                    if not callback_sent:
                        display.debug(
                            "sending task start callback, copying the task so we can template it temporarily"
                        )
                        saved_name = task.name
                        display.debug("done copying, going to template now")
                        try:
                            task.name = to_text(
                                templar.template(task.name, fail_on_undefined=False),
                                nonstring="empty",
                            )
                            display.debug("done templating")
                        except:
                            # just ignore any errors during task name templating,
                            # we don't care if it just shows the raw name
                            display.debug("templating failed for some reason")
                            pass
                        display.debug("here goes the callback...")
                        self._tqm.send_callback(
                            "v2_playbook_on_task_start", task, is_conditional=False
                        )
                        task.name = saved_name
                        callback_sent = True
                        display.debug("sending task start callback")

                    self._blocked_hosts[host.get_name()] = True
                    self._queue_task(host, task, task_vars, play_context)
                    del task_vars

                # if we're bypassing the host loop, break out now
                if run_once:
                    break

                results += self._process_pending_results(
                    iterator, max_passes=max(1, int(len(self._tqm._workers) * 0.1))
                )

            # go to next host/task group
            if skip_rest:
                continue

            display.debug(
                "done queuing things up, now waiting for results queue to drain"
            )
            if self._pending_results > 0:
                results += self._wait_on_pending_results(iterator)
            host_results.extend(results)

            all_role_blocks = []
            for hr in results:
                # handle include_role
                if hr._task.action == "include_role":
                    loop_var = None
                    if hr._task.loop:
                        loop_var = "item"
                        if hr._task.loop_control:
                            loop_var = hr._task.loop_control.loop_var or "item"
                        include_results = hr._result.get("results", [])
                    else:
                        include_results = [hr._result]

                    for include_result in include_results:
                        if (
                            "skipped" in include_result
                            and include_result["skipped"]
                            or "failed" in include_result
                            and include_result["failed"]
                        ):
                            continue

                        display.debug("generating all_blocks data for role")
                        new_ir = hr._task.copy()
                        new_ir.vars.update(
                            include_result.get("include_variables", dict())
                        )
                        if loop_var and loop_var in include_result:
                            new_ir.vars[loop_var] = include_result[loop_var]

                        all_role_blocks.extend(
                            new_ir.get_block_list(
                                play=iterator._play,
                                variable_manager=self._variable_manager,
                                loader=self._loader,
                            )
                        )

            if len(all_role_blocks) > 0:
                for host in hosts_left:
                    iterator.add_tasks(host, all_role_blocks)

            try:
                included_files = IncludedFile.process_include_results(
                    host_results,
                    self._tqm,
                    iterator=iterator,
                    inventory=self._inventory,
                    loader=self._loader,
                    variable_manager=self._variable_manager,
                )
            except AnsibleError as e:
                # this is a fatal error, so we abort here regardless of block state
                return self._tqm.RUN_ERROR

            include_failure = False
            if len(included_files) > 0:
                display.debug("we have included files to process")
                noop_task = Task()
                noop_task.action = "meta"
                noop_task.args["_raw_params"] = "noop"
                noop_task.set_loader(iterator._play._loader)

                display.debug("generating all_blocks data")
                all_blocks = dict((host, []) for host in hosts_left)
                display.debug("done generating all_blocks data")
                for included_file in included_files:
                    display.debug(
                        "processing included file: %s" % included_file._filename
                    )
                    # included hosts get the task list while those excluded get an equal-length
                    # list of noop tasks, to make sure that they continue running in lock-step
                    try:
                        new_blocks = self._load_included_file(
                            included_file, iterator=iterator
                        )

                        display.debug(
                            "iterating over new_blocks loaded from include file"
                        )
                        for new_block in new_blocks:
                            task_vars = self._variable_manager.get_vars(
                                loader=self._loader,
                                play=iterator._play,
                                task=included_file._task,
                            )
                            display.debug("filtering new block on tags")
                            final_block = new_block.filter_tagged_tasks(
                                play_context, task_vars
                            )
                            display.debug("done filtering new block on tags")

                            noop_block = Block(parent_block=task._parent)
                            noop_block.block = [noop_task for t in new_block.block]
                            noop_block.always = [noop_task for t in new_block.always]
                            noop_block.rescue = [noop_task for t in new_block.rescue]

                            for host in hosts_left:
                                if host in included_file._hosts:
                                    all_blocks[host].append(final_block)
                                else:
                                    all_blocks[host].append(noop_block)
                        display.debug(
                            "done iterating over new_blocks loaded from include file"
                        )

                    except AnsibleError as e:
                        for host in included_file._hosts:
                            self._tqm._failed_hosts[host.name] = True
                            iterator.mark_host_failed(host)
                        display.error(to_text(e), wrap_text=False)
                        include_failure = True
                        continue

                # finally go through all of the hosts and append the
                # accumulated blocks to their list of tasks
                display.debug("extending task lists for all hosts with included blocks")

                for host in hosts_left:
                    iterator.add_tasks(host, all_blocks[host])

                display.debug("done extending task lists")
                display.debug("done processing included files")

            display.debug("results queue empty")

            display.debug("checking for any_errors_fatal")
            failed_hosts = []
            unreachable_hosts = []
            for res in results:
                if res.is_failed() and iterator.is_failed(res._host):
                    failed_hosts.append(res._host.name)
                elif res.is_unreachable():
                    unreachable_hosts.append(res._host.name)

            # if any_errors_fatal and we had an error, mark all hosts as failed
            if any_errors_fatal and (
                len(failed_hosts) > 0 or len(unreachable_hosts) > 0
            ):
                for host in hosts_left:
                    (s, _) = iterator.get_next_task_for_host(host, peek=True)
                    if (
                        s.run_state != iterator.ITERATING_RESCUE
                        or s.run_state == iterator.ITERATING_RESCUE
                        and s.fail_state & iterator.FAILED_RESCUE != 0
                    ):
                        self._tqm._failed_hosts[host.name] = True
                        result |= self._tqm.RUN_FAILED_BREAK_PLAY
            display.debug("done checking for any_errors_fatal")

            display.debug("checking for max_fail_percentage")
            if iterator._play.max_fail_percentage is not None and len(results) > 0:
                percentage = iterator._play.max_fail_percentage / 100.0

                if (len(self._tqm._failed_hosts) / len(results)) > percentage:
                    for host in hosts_left:
                        # don't double-mark hosts, or the iterator will potentially
                        # fail them out of the rescue/always states
                        if host.name not in failed_hosts:
                            self._tqm._failed_hosts[host.name] = True
                            iterator.mark_host_failed(host)
                    self._tqm.send_callback("v2_playbook_on_no_hosts_remaining")
                    result |= self._tqm.RUN_FAILED_BREAK_PLAY
            display.debug("done checking for max_fail_percentage")

            display.debug(
                "checking to see if all hosts have failed and the running result is not ok"
            )
            if result != self._tqm.RUN_OK and len(self._tqm._failed_hosts) >= len(
                hosts_left
            ):
                display.debug("^ not ok, so returning result now")
                self._tqm.send_callback("v2_playbook_on_no_hosts_remaining")
                return result
            display.debug("done checking to see if all hosts have failed")

        except (IOError, EOFError) as e:
            display.debug("got IOError/EOFError in task loop: %s" % e)
            # most likely an abort, return failed
            return self._tqm.RUN_UNKNOWN_ERROR

    # run the base class run() method, which executes the cleanup function
    # and runs any outstanding handlers which have been triggered

    return super(StrategyModule, self).run(iterator, play_context, result)


# Traceback (KeyError)
ansible-playbook -vvvv playbook.yml
No config file found; using defaults
[WARNING]: Host file not found: /etc/ansible/hosts

[WARNING]: provided hosts list is empty, only localhost is available

Loading callback plugin default of type stdout, v2.0 from /usr/local/lib/python2.7/site-packages/ansible/plugins/callback/__init__.pyc

PLAYBOOK: playbook.yml *********************************************************
1 plays in playbook.yml

PLAY [localhost] ***************************************************************

TASK [include_role] ************************************************************
task path: /Users/xxx/workspace/xxx/playbook.yml:6

TASK [handlertest : command] ***************************************************
task path: /Users/xxx/workspace/xxx/roles/handlertest/tasks/main.yml:3
Using module file /usr/local/lib/python2.7/site-packages/ansible/modules/core/commands/command.py
<127.0.0.1> ESTABLISH LOCAL CONNECTION FOR USER: xxx
<127.0.0.1> EXEC /bin/sh -c '( umask 77 &amp;&amp; mkdir -p "` echo $HOME/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975 `" &amp;&amp; echo ansible-tmp-1478572148.78-187995060050975="` echo $HOME/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975 `" ) &amp;&amp; sleep 0'
<127.0.0.1> PUT /var/folders/62/pqgvprd11fb4k6shw2pdzkqm0000gq/T/tmpGA2Gau TO /Users/xxx/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975/command.py
<127.0.0.1> EXEC /bin/sh -c 'chmod u+x /Users/xxx/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975/ /Users/xxx/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975/command.py &amp;&amp; sleep 0'
<127.0.0.1> EXEC /bin/sh -c '/usr/local/opt/python/bin/python2.7 /Users/xxx/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975/command.py; rm -rf "/Users/xxx/.ansible/tmp/ansible-tmp-1478572148.78-187995060050975/" > /dev/null 2>&amp;1 &amp;&amp; sleep 0'
ERROR! Unexpected Exception: HANDLER: handlertest : Some handler
the full traceback was:

Traceback (most recent call last):
File "/usr/local/bin/ansible-playbook", line 103, in <module>
exit_code = cli.run()
File "/usr/local/lib/python2.7/site-packages/ansible/cli/playbook.py", line 159, in run
results = pbex.run()
File "/usr/local/lib/python2.7/site-packages/ansible/executor/playbook_executor.py", line 154, in run
result = self._tqm.run(play=play)
File "/usr/local/lib/python2.7/site-packages/ansible/executor/task_queue_manager.py", line 282, in run
play_return = strategy.run(iterator, play_context)
File "/usr/local/lib/python2.7/site-packages/ansible/plugins/strategy/linear.py", line 278, in run
results += self._wait_on_pending_results(iterator)
File "/usr/local/lib/python2.7/site-packages/ansible/plugins/strategy/__init__.py", line 534, in _wait_on_pending_results
results = self._process_pending_results(iterator)
File "/usr/local/lib/python2.7/site-packages/ansible/plugins/strategy/__init__.py", line 399, in _process_pending_results
if original_host not in self._notified_handlers[target_handler]:
KeyError: HANDLER: handlertest : Some handler

# Fixed code
def run(self, iterator, play_context):
    """
    The linear strategy is simple - get the next task and queue
    it for all hosts, then wait for the queue to drain before
    moving on to the next task
    """

    # iteratate over each task, while there is one left to run
    result = self._tqm.RUN_OK
    work_to_do = True
    while work_to_do and not self._tqm._terminated:
        try:
            display.debug("getting the remaining hosts for this loop")
            hosts_left = [
                host
                for host in self._inventory.get_hosts(iterator._play.hosts)
                if host.name not in self._tqm._unreachable_hosts
            ]
            display.debug("done getting the remaining hosts for this loop")

            # queue up this task for each host in the inventory
            callback_sent = False
            work_to_do = False

            host_results = []
            host_tasks = self._get_next_task_lockstep(hosts_left, iterator)

            # skip control
            skip_rest = False
            choose_step = True

            # flag set if task is set to any_errors_fatal
            any_errors_fatal = False

            results = []
            for host, task in host_tasks:
                if not task:
                    continue

                if self._tqm._terminated:
                    break

                run_once = False
                work_to_do = True

                # test to see if the task across all hosts points to an action plugin which
                # sets BYPASS_HOST_LOOP to true, or if it has run_once enabled. If so, we
                # will only send this task to the first host in the list.

                try:
                    action = action_loader.get(task.action, class_only=True)
                except KeyError:
                    # we don't care here, because the action may simply not have a
                    # corresponding action plugin
                    action = None

                # check to see if this task should be skipped, due to it being a member of a
                # role which has already run (and whether that role allows duplicate execution)
                if task._role and task._role.has_run(host):
                    # If there is no metadata, the default behavior is to not allow duplicates,
                    # if there is metadata, check to see if the allow_duplicates flag was set to true
                    if (
                        task._role._metadata is None
                        or task._role._metadata
                        and not task._role._metadata.allow_duplicates
                    ):
                        display.debug(
                            "'%s' skipped because role has already run" % task
                        )
                        continue

                if task.action == "meta":
                    # for the linear strategy, we run meta tasks just once and for
                    # all hosts currently being iterated over rather than one host
                    results.extend(
                        self._execute_meta(task, play_context, iterator, host)
                    )
                    if task.args.get("_raw_params", None) != "noop":
                        run_once = True
                else:
                    # handle step if needed, skip meta actions as they are used internally
                    if self._step and choose_step:
                        if self._take_step(task):
                            choose_step = False
                        else:
                            skip_rest = True
                            break

                    display.debug("getting variables")
                    task_vars = self._variable_manager.get_vars(
                        loader=self._loader, play=iterator._play, host=host, task=task
                    )
                    self.add_tqm_variables(task_vars, play=iterator._play)
                    templar = Templar(loader=self._loader, variables=task_vars)
                    display.debug("done getting variables")

                    run_once = (
                        templar.template(task.run_once)
                        or action
                        and getattr(action, "BYPASS_HOST_LOOP", False)
                    )

                    if (task.any_errors_fatal or run_once) and not task.ignore_errors:
                        any_errors_fatal = True

                    if not callback_sent:
                        display.debug(
                            "sending task start callback, copying the task so we can template it temporarily"
                        )
                        saved_name = task.name
                        display.debug("done copying, going to template now")
                        try:
                            task.name = to_text(
                                templar.template(task.name, fail_on_undefined=False),
                                nonstring="empty",
                            )
                            display.debug("done templating")
                        except:
                            # just ignore any errors during task name templating,
                            # we don't care if it just shows the raw name
                            display.debug("templating failed for some reason")
                            pass
                        display.debug("here goes the callback...")
                        self._tqm.send_callback(
                            "v2_playbook_on_task_start", task, is_conditional=False
                        )
                        task.name = saved_name
                        callback_sent = True
                        display.debug("sending task start callback")

                    self._blocked_hosts[host.get_name()] = True
                    self._queue_task(host, task, task_vars, play_context)
                    del task_vars

                # if we're bypassing the host loop, break out now
                if run_once:
                    break

                results += self._process_pending_results(
                    iterator, max_passes=max(1, int(len(self._tqm._workers) * 0.1))
                )

            # go to next host/task group
            if skip_rest:
                continue

            display.debug(
                "done queuing things up, now waiting for results queue to drain"
            )
            if self._pending_results > 0:
                results += self._wait_on_pending_results(iterator)
            host_results.extend(results)

            all_role_blocks = []
            for hr in results:
                # handle include_role
                if hr._task.action == "include_role":
                    loop_var = None
                    if hr._task.loop:
                        loop_var = "item"
                        if hr._task.loop_control:
                            loop_var = hr._task.loop_control.loop_var or "item"
                        include_results = hr._result.get("results", [])
                    else:
                        include_results = [hr._result]

                    for include_result in include_results:
                        if (
                            "skipped" in include_result
                            and include_result["skipped"]
                            or "failed" in include_result
                            and include_result["failed"]
                        ):
                            continue

                        display.debug("generating all_blocks data for role")
                        new_ir = hr._task.copy()
                        new_ir.vars.update(
                            include_result.get("include_variables", dict())
                        )
                        if loop_var and loop_var in include_result:
                            new_ir.vars[loop_var] = include_result[loop_var]

                        blocks, handler_blocks = new_ir.get_block_list(
                            play=iterator._play,
                            variable_manager=self._variable_manager,
                            loader=self._loader,
                        )
                        all_role_blocks.extend(blocks)
                        self._tqm.update_handler_list(
                            [
                                handler
                                for handler_block in handler_blocks
                                for handler in handler_block.block
                            ]
                        )

            if len(all_role_blocks) > 0:
                for host in hosts_left:
                    iterator.add_tasks(host, all_role_blocks)

            try:
                included_files = IncludedFile.process_include_results(
                    host_results,
                    self._tqm,
                    iterator=iterator,
                    inventory=self._inventory,
                    loader=self._loader,
                    variable_manager=self._variable_manager,
                )
            except AnsibleError as e:
                # this is a fatal error, so we abort here regardless of block state
                return self._tqm.RUN_ERROR

            include_failure = False
            if len(included_files) > 0:
                display.debug("we have included files to process")
                noop_task = Task()
                noop_task.action = "meta"
                noop_task.args["_raw_params"] = "noop"
                noop_task.set_loader(iterator._play._loader)

                display.debug("generating all_blocks data")
                all_blocks = dict((host, []) for host in hosts_left)
                display.debug("done generating all_blocks data")
                for included_file in included_files:
                    display.debug(
                        "processing included file: %s" % included_file._filename
                    )
                    # included hosts get the task list while those excluded get an equal-length
                    # list of noop tasks, to make sure that they continue running in lock-step
                    try:
                        new_blocks = self._load_included_file(
                            included_file, iterator=iterator
                        )

                        display.debug(
                            "iterating over new_blocks loaded from include file"
                        )
                        for new_block in new_blocks:
                            task_vars = self._variable_manager.get_vars(
                                loader=self._loader,
                                play=iterator._play,
                                task=included_file._task,
                            )
                            display.debug("filtering new block on tags")
                            final_block = new_block.filter_tagged_tasks(
                                play_context, task_vars
                            )
                            display.debug("done filtering new block on tags")

                            noop_block = Block(parent_block=task._parent)
                            noop_block.block = [noop_task for t in new_block.block]
                            noop_block.always = [noop_task for t in new_block.always]
                            noop_block.rescue = [noop_task for t in new_block.rescue]

                            for host in hosts_left:
                                if host in included_file._hosts:
                                    all_blocks[host].append(final_block)
                                else:
                                    all_blocks[host].append(noop_block)
                        display.debug(
                            "done iterating over new_blocks loaded from include file"
                        )

                    except AnsibleError as e:
                        for host in included_file._hosts:
                            self._tqm._failed_hosts[host.name] = True
                            iterator.mark_host_failed(host)
                        display.error(to_text(e), wrap_text=False)
                        include_failure = True
                        continue

                # finally go through all of the hosts and append the
                # accumulated blocks to their list of tasks
                display.debug("extending task lists for all hosts with included blocks")

                for host in hosts_left:
                    iterator.add_tasks(host, all_blocks[host])

                display.debug("done extending task lists")
                display.debug("done processing included files")

            display.debug("results queue empty")

            display.debug("checking for any_errors_fatal")
            failed_hosts = []
            unreachable_hosts = []
            for res in results:
                if res.is_failed() and iterator.is_failed(res._host):
                    failed_hosts.append(res._host.name)
                elif res.is_unreachable():
                    unreachable_hosts.append(res._host.name)

            # if any_errors_fatal and we had an error, mark all hosts as failed
            if any_errors_fatal and (
                len(failed_hosts) > 0 or len(unreachable_hosts) > 0
            ):
                for host in hosts_left:
                    (s, _) = iterator.get_next_task_for_host(host, peek=True)
                    if (
                        s.run_state != iterator.ITERATING_RESCUE
                        or s.run_state == iterator.ITERATING_RESCUE
                        and s.fail_state & iterator.FAILED_RESCUE != 0
                    ):
                        self._tqm._failed_hosts[host.name] = True
                        result |= self._tqm.RUN_FAILED_BREAK_PLAY
            display.debug("done checking for any_errors_fatal")

            display.debug("checking for max_fail_percentage")
            if iterator._play.max_fail_percentage is not None and len(results) > 0:
                percentage = iterator._play.max_fail_percentage / 100.0

                if (len(self._tqm._failed_hosts) / len(results)) > percentage:
                    for host in hosts_left:
                        # don't double-mark hosts, or the iterator will potentially
                        # fail them out of the rescue/always states
                        if host.name not in failed_hosts:
                            self._tqm._failed_hosts[host.name] = True
                            iterator.mark_host_failed(host)
                    self._tqm.send_callback("v2_playbook_on_no_hosts_remaining")
                    result |= self._tqm.RUN_FAILED_BREAK_PLAY
            display.debug("done checking for max_fail_percentage")

            display.debug(
                "checking to see if all hosts have failed and the running result is not ok"
            )
            if result != self._tqm.RUN_OK and len(self._tqm._failed_hosts) >= len(
                hosts_left
            ):
                display.debug("^ not ok, so returning result now")
                self._tqm.send_callback("v2_playbook_on_no_hosts_remaining")
                return result
            display.debug("done checking to see if all hosts have failed")

        except (IOError, EOFError) as e:
            display.debug("got IOError/EOFError in task loop: %s" % e)
            # most likely an abort, return failed
            return self._tqm.RUN_UNKNOWN_ERROR

    # run the base class run() method, which executes the cleanup function
    # and runs any outstanding handlers which have been triggered

    return super(StrategyModule, self).run(iterator, play_context, result)