1 files changed, 81 insertions, 0 deletions
diff --git a/taskcluster/taskgraph/util/backstop.py b/taskcluster/taskgraph/util/backstop.py
new file mode 100644
index 0000000000..e89cd53ef0
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+++ b/taskcluster/taskgraph/util/backstop.py
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+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+from requests import HTTPError
+
+from taskgraph.util.taskcluster import (
+    find_task_id,
+    get_artifact,
+    status_task,
+)
+
+
+BACKSTOP_PUSH_INTERVAL = 20
+BACKSTOP_TIME_INTERVAL = 60 * 4  # minutes
+BACKSTOP_INDEX = "gecko.v2.{project}.latest.taskgraph.backstop"
+
+
+def is_backstop(
+    params, push_interval=BACKSTOP_PUSH_INTERVAL, time_interval=BACKSTOP_TIME_INTERVAL
+):
+    """Determines whether the given parameters represent a backstop push.
+
+    Args:
+        push_interval (int): Number of pushes
+        time_interval (int): Minutes between forced schedules.
+                             Use 0 to disable.
+    Returns:
+        bool: True if this is a backtop, otherwise False.
+    """
+    # In case this is being faked on try.
+    if params.get("backstop", False):
+        return True
+
+    project = params["project"]
+    pushid = int(params["pushlog_id"])
+    pushdate = int(params["pushdate"])
+
+    if project == "try":
+        return False
+    elif project != "autoland":
+        return True
+
+    # On every Nth push, want to run all tasks.
+    if pushid % push_interval == 0:
+        return True
+
+    if time_interval <= 0:
+        return False
+
+    # We also want to ensure we run all tasks at least once per N minutes.
+    index = BACKSTOP_INDEX.format(project=project)
+
+    try:
+        last_backstop_id = find_task_id(index)
+    except KeyError:
+        # Index wasn't found, implying there hasn't been a backstop push yet.
+        return True
+
+    if status_task(last_backstop_id) in ("failed", "exception"):
+        # If the last backstop failed its decision task, make this a backstop.
+        return True
+
+    try:
+        last_pushdate = get_artifact(last_backstop_id, "public/parameters.yml")[
+            "pushdate"
+        ]
+    except HTTPError as e:
+        # If the last backstop decision task exists in the index, but
+        # parameters.yml isn't available yet, it means the decision task is
+        # still running. If that's the case, we can be pretty sure the time
+        # component will not cause a backstop, so just return False.
+        if e.response.status_code == 404:
+            return False
+        raise
+
+    if (pushdate - last_pushdate) / 60 >= time_interval:
+        return True
+    return False