The initial implementation of the edit monitor
Creates a class that will manager and monitor the actual edit watchdog
that run as a subprocess. As a first step, the class supports:
1) A start method that creates a pidfile and starts a subprocess with given target/args.
2) A stop method that terminates the created subprocess and removes the pidfile.
Detailed design in go/android-local-edit-monitor.
Test: atest daemon_manager_test
bug: 365617369
Change-Id: Ic6d7be67d284ade8033416235b9b0fb1e90e1b1a
diff --git a/tools/edit_monitor/daemon_manager.py b/tools/edit_monitor/daemon_manager.py
new file mode 100644
index 0000000..c09c321
--- /dev/null
+++ b/tools/edit_monitor/daemon_manager.py
@@ -0,0 +1,165 @@
+# Copyright 2024, The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import hashlib
+import logging
+import multiprocessing
+import os
+import pathlib
+import signal
+import subprocess
+import tempfile
+import time
+
+
+DEFAULT_PROCESS_TERMINATION_TIMEOUT_SECONDS = 1
+
+
+def default_daemon_target():
+ """Place holder for the default daemon target."""
+ print("default daemon target")
+
+
+class DaemonManager:
+ """Class to manage and monitor the daemon run as a subprocess."""
+
+ def __init__(
+ self,
+ binary_path: str,
+ daemon_target: callable = default_daemon_target,
+ daemon_args: tuple = (),
+ ):
+ self.binary_path = binary_path
+ self.daemon_target = daemon_target
+ self.daemon_args = daemon_args
+
+ self.pid = os.getpid()
+ self.daemon_process = None
+
+ pid_file_dir = pathlib.Path(tempfile.gettempdir()).joinpath("edit_monitor")
+ pid_file_dir.mkdir(parents=True, exist_ok=True)
+ self.pid_file_path = self._get_pid_file_path(pid_file_dir)
+
+ def start(self):
+ """Writes the pidfile and starts the daemon proces."""
+ try:
+ self._write_pid_to_pidfile()
+ self._start_daemon_process()
+ except Exception as e:
+ logging.exception("Failed to start daemon manager with error %s", e)
+
+ def stop(self):
+ """Stops the daemon process and removes the pidfile."""
+
+ logging.debug("in daemon manager cleanup.")
+ try:
+ if self.daemon_process and self.daemon_process.is_alive():
+ self._terminate_process(self.daemon_process.pid)
+ self._remove_pidfile()
+ except Exception as e:
+ logging.exception("Failed to stop daemon manager with error %s", e)
+
+ def _write_pid_to_pidfile(self):
+ """Creates a pidfile and writes the current pid to the file.
+
+ Raise FileExistsError if the pidfile already exists.
+ """
+ try:
+ # Use the 'x' mode to open the file for exclusive creation
+ with open(self.pid_file_path, "x") as f:
+ f.write(f"{self.pid}")
+ except FileExistsError as e:
+ # This could be caused due to race condition that a user is trying
+ # to start two edit monitors at the same time. Or because there is
+ # already an existing edit monitor running and we can not kill it
+ # for some reason.
+ logging.exception("pidfile %s already exists.", self.pid_file_path)
+ raise e
+
+ def _start_daemon_process(self):
+ """Starts a subprocess to run the daemon."""
+ p = multiprocessing.Process(
+ target=self.daemon_target, args=self.daemon_args
+ )
+ p.start()
+
+ logging.info("Start subprocess with PID %d", p.pid)
+ self.daemon_process = p
+
+ def _terminate_process(
+ self, pid: int, timeout: int = DEFAULT_PROCESS_TERMINATION_TIMEOUT_SECONDS
+ ):
+ """Terminates a process with given pid.
+
+ It first sends a SIGTERM to the process to allow it for proper
+ termination with a timeout. If the process is not terminated within
+ the timeout, kills it forcefully.
+ """
+ try:
+ os.kill(pid, signal.SIGTERM)
+ if not self._wait_for_process_terminate(pid, timeout):
+ logging.warning(
+ "Process %d not terminated within timeout, try force kill", pid
+ )
+ os.kill(pid, signal.SIGKILL)
+ except ProcessLookupError:
+ logging.info("Process with PID %d not found (already terminated)", pid)
+
+ def _wait_for_process_terminate(self, pid: int, timeout: int) -> bool:
+ start_time = time.time()
+
+ while time.time() < start_time + timeout:
+ if not self._is_process_alive(pid):
+ return True
+ time.sleep(1)
+
+ logging.error("Process %d not terminated within %d seconds.", pid, timeout)
+ return False
+
+ def _is_process_alive(self, pid: int) -> bool:
+ try:
+ output = subprocess.check_output(
+ ["ps", "-p", str(pid), "-o", "state="], text=True
+ ).strip()
+ state = output.split()[0]
+ return state != "Z" # Check if the state is not 'Z' (zombie)
+ except subprocess.CalledProcessError:
+ # Process not found (already dead).
+ return False
+ except (FileNotFoundError, OSError, ValueError) as e:
+ logging.warning(
+ "Unable to check the status for process %d with error: %s.", pid, e
+ )
+ return True
+
+ def _remove_pidfile(self):
+ try:
+ os.remove(self.pid_file_path)
+ except FileNotFoundError:
+ logging.info("pid file %s already removed.", self.pid_file_path)
+
+ def _get_pid_file_path(self, pid_file_dir: pathlib.Path) -> pathlib.Path:
+ """Generates the path to store the pidfile.
+
+ The file path should have the format of "/tmp/edit_monitor/xxxx.lock"
+ where xxxx is a hashed value based on the binary path that starts the
+ process.
+ """
+ hash_object = hashlib.sha256()
+ hash_object.update(self.binary_path.encode("utf-8"))
+ pid_file_path = pid_file_dir.joinpath(hash_object.hexdigest() + ".lock")
+ logging.info("pid_file_path: %s", pid_file_path)
+
+ return pid_file_path