move the custom exclusive process code from utils.py into a new python package named exclusiveprocess

management/backup.py

@@ -10,8 +10,9 @@
 import os, os.path, shutil, glob, re, datetime, sys
 import dateutil.parser, dateutil.relativedelta, dateutil.tz
 import rtyaml
+from exclusiveprocess import Lock
 
-from utils import exclusive_process, load_environment, shell, wait_for_service, fix_boto
+from utils import load_environment, shell, wait_for_service, fix_boto
 
 rsync_ssh_options = [
 	"--ssh-options='-i /root/.ssh/id_rsa_miab'",
@@ -204,7 +205,10 @@ def get_target_type(config):
 def perform_backup(full_backup):
 	env = load_environment()
 
-	exclusive_process("backup")
+	# Create an global exclusive lock so that the backup script
+	# cannot be run more than one.
+	Lock(die=True).forever()
+
 	config = get_backup_config(env)
 	backup_root = os.path.join(env["STORAGE_ROOT"], 'backup')
 	backup_cache_dir = os.path.join(backup_root, 'cache')

management/ssl_certificates.py

@@ -411,9 +411,11 @@ def provision_certificates(env, agree_to_tos_url=None, logger=None, show_extende
 
 def provision_certificates_cmdline():
 	import sys
-	from utils import load_environment, exclusive_process
+	from exclusiveprocess import Lock
 
-	exclusive_process("update_tls_certificates")
+	from utils import load_environment
+
+	Lock(die=True).forever()
 	env = load_environment()
 
 	verbose = False

management/utils.py

@@ -106,76 +106,6 @@ def sort_email_addresses(email_addresses, env):
     ret.extend(sorted(email_addresses)) # whatever is left
     return ret
 
-def exclusive_process(name):
-    # Ensure that a process named `name` does not execute multiple
-    # times concurrently.
-    import os, sys, atexit
-    pidfile = '/var/run/mailinabox-%s.pid' % name
-    mypid = os.getpid()
-
-    # Attempt to get a lock on ourself so that the concurrency check
-    # itself is not executed in parallel.
-    with open(__file__, 'r+') as flock:
-        # Try to get a lock. This blocks until a lock is acquired. The
-        # lock is held until the flock file is closed at the end of the
-        # with block.
-        os.lockf(flock.fileno(), os.F_LOCK, 0)
-
-        # While we have a lock, look at the pid file. First attempt
-        # to write our pid to a pidfile if no file already exists there.
-        try:
-            with open(pidfile, 'x') as f:
-                # Successfully opened a new file. Since the file is new
-                # there is no concurrent process. Write our pid.
-                f.write(str(mypid))
-                atexit.register(clear_my_pid, pidfile)
-                return
-        except FileExistsError:
-            # The pid file already exixts, but it may contain a stale
-            # pid of a terminated process.
-            with open(pidfile, 'r+') as f:
-                # Read the pid in the file.
-                existing_pid = None
-                try:
-                    existing_pid = int(f.read().strip())
-                except ValueError:
-                    pass # No valid integer in the file.
-
-                # Check if the pid in it is valid.
-                if existing_pid:
-                    if is_pid_valid(existing_pid):
-                        print("Another %s is already running (pid %d)." % (name, existing_pid), file=sys.stderr)
-                        sys.exit(1)
-
-                # Write our pid.
-                f.seek(0)
-                f.write(str(mypid))
-                f.truncate()
-                atexit.register(clear_my_pid, pidfile)
- 
-
-def clear_my_pid(pidfile):
-    import os
-    os.unlink(pidfile)
-
-
-def is_pid_valid(pid):
-    """Checks whether a pid is a valid process ID of a currently running process."""
-    # adapted from http://stackoverflow.com/questions/568271/how-to-check-if-there-exists-a-process-with-a-given-pid
-    import os, errno
-    if pid <= 0: raise ValueError('Invalid PID.')
-    try:
-        os.kill(pid, 0)
-    except OSError as err:
-        if err.errno == errno.ESRCH: # No such process
-            return False
-        elif err.errno == errno.EPERM: # Not permitted to send signal
-            return True
-        else: # EINVAL
-            raise
-    else:
-        return True
-
 def shell(method, cmd_args, env={}, capture_stderr=False, return_bytes=False, trap=False, input=None):
     # A safe way to execute processes.
     # Some processes like apt-get require being given a sane PATH.

setup/management.sh

@@ -16,7 +16,7 @@ apt_install build-essential libssl-dev libffi-dev python3-dev
 # The first line is the packages that Josh maintains himself!
 # NOTE: email_validator is repeated in setup/questions.sh, so please keep the versions synced.
 hide_output pip3 install --upgrade \
-	rtyaml "email_validator>=1.0.0" "free_tls_certificates>=0.1.3" \
+	rtyaml "email_validator>=1.0.0" "free_tls_certificates>=0.1.3" "exclusiveprocess" \
 	"idna>=2.0.0" "cryptography>=1.0.2" boto psutil
 
 # duplicity uses python 2 so we need to get the python 2 package of boto to have backups to S3.