Merge ~jfguedez/charm-juju-lint:bug/1942946 into charm-juju-lint:master

[Jose Guedez]

Prevent auto_lint.py from running more than one instance simultaneously

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Failed to merge change (unable to merge source repository due to conflicts), setting status to needs review.

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 643e1a1b45feec5ea614841323d7e806811cda68

diff --git a/scripts/auto_lint.py b/scripts/auto_lint.py
index 0c5fc11..cbc4389 100755
--- a/scripts/auto_lint.py
+++ b/scripts/auto_lint.py
@@ -24,6 +24,7 @@ from base64 import b64decode
 import json
 import logging
 from os.path import join
+import os
 import subprocess
 from sys import exit
 
@@ -35,6 +36,7 @@ VAR_LIB = "/var/snap/juju-lint/common"
 LINT_CONFIG_PATH = join(VAR_LIB, "auto-lint-config.json")
 JUJU_STATUS_PATH = join(VAR_LIB, "juju-status.json")
 LINT_RESULTS_PATH = join(VAR_LIB, "lint-results.txt")
+PID_FILENAME = "/tmp/auto_lint.pid"
 
 # Deal with https://github.com/juju/python-libjuju/issues/136, set to 32MB
 MAX_FRAME_SIZE = 2 ** 25
@@ -244,13 +246,26 @@ def main():
     loglevel = logging.DEBUG if args.debug else logging.ERROR
     logging.basicConfig(level=loglevel)
 
-    auto_lint_config = read_json_file(LINT_CONFIG_PATH)
-    verify_auto_lint_config(auto_lint_config)
-    juju_status = loop.run(get_juju_status(auto_lint_config))
-    write_file(
-        JUJU_STATUS_PATH, json.dumps(juju_status, cls=TypeEncoder, sort_keys=True)
-    )
-    lint_juju(auto_lint_config)
+    # Ensure a single instance via a simple pidfile
+    pid = str(os.getpid())
+
+    if os.path.isfile(PID_FILENAME):
+        exit("{} already exists, exiting".format(PID_FILENAME))
+
+    with open(PID_FILENAME, "w") as f:
+        f.write(pid)
+
+    # Read config, get juju model information and lint it
+    try:
+        auto_lint_config = read_json_file(LINT_CONFIG_PATH)
+        verify_auto_lint_config(auto_lint_config)
+        juju_status = loop.run(get_juju_status(auto_lint_config))
+        write_file(
+            JUJU_STATUS_PATH, json.dumps(juju_status, cls=TypeEncoder, sort_keys=True)
+        )
+        lint_juju(auto_lint_config)
+    finally:
+        os.unlink(PID_FILENAME)
 
 
 if __name__ == "__main__":