CI: fast finish travis builds for the same PR

closes pandas-dev#12438

Author: jreback

ci/install_travis.sh

@@ -1,17 +1,8 @@
 #!/bin/bash
 
-# There are 2 distinct pieces that get zipped and cached
-# - The venv site-packages dir including the installed dependencies
-# - The pandas build artifacts, using the build cache support via
-#   scripts/use_build_cache.py
-#
-# if the user opted in to use the cache and we're on a whitelisted fork
-# - if the server doesn't hold a cached version of venv/pandas build,
-#   do things the slow way, and put the results on the cache server
-#   for the next time.
-# -  if the cache files are available, instal some necessaries via apt
-#    (no compiling needed), then directly goto script and collect 200$.
-#
+# Fast finish the PR if we have an existing one
+echo "[Checking to see if this build is outdated]"
+ci/travis_fast_finish.py || { echo "Failing outdated build to end it."; exit 1; }
 
 function edit_init()
 {

ci/travis_fast_finish.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python
+
+# script to cancel previous travis builds for the same PR
+# originally from
+# https://github.com/conda-forge/staged-recipes/pull/2257
+
+try:
+    from future_builtins import (
+        map,
+        filter,
+    )
+except ImportError:
+    pass
+
+import codecs
+import contextlib
+import json
+import os
+
+try:
+    from urllib.request import (
+        Request,
+        urlopen,
+    )
+except ImportError:
+    from urllib2 import (
+        Request,
+        urlopen,
+    )
+
+
+def check_latest_pr_build(repo, pr, build_num):
+    # Not a PR so it is latest.
+    if pr is None:
+        return True
+
+    headers = {
+        "Accept": "application/vnd.travis-ci.2+json",
+    }
+    url = "https://api.travis-ci.org/repos/{repo}/builds?event_type=pull_request"
+
+    request = Request(url.format(repo=repo), headers=headers)
+    with contextlib.closing(urlopen(request)) as response:
+        reader = codecs.getreader("utf-8")
+        data = json.load(reader(response))
+
+    # Parse the response to get a list of build numbers for this PR.
+    builds = data["builds"]
+    pr_builds = filter(lambda b: b["pull_request_number"] == pr, builds)
+    pr_build_nums = sorted(map(lambda b: int(b["number"]), pr_builds))
+
+    # Check if our build number is the latest (largest)
+    # out of all of the builds for this PR.
+    if build_num < max(pr_build_nums):
+        return False
+    else:
+        return True
+
+
+def main():
+    repo = os.environ["TRAVIS_REPO_SLUG"]
+
+    pr = os.environ["TRAVIS_PULL_REQUEST"]
+    pr = None if pr == "false" else int(pr)
+
+    build_num = int(os.environ["TRAVIS_BUILD_NUMBER"])
+
+    return int(check_latest_pr_build(repo, pr, build_num) is False)
+
+
+if __name__ == "__main__":
+    import sys
+    sys.exit(main())