add a fairly basic file locking mechanism with src/LockFile.py

closes #96

4 files changed, 57 insertions, 6 deletions

diff --git a/src/IRCBot.py b/src/IRCBot.py
index df0b0540..f9493367 100644
--- a/src/IRCBot.py
+++ b/src/IRCBot.py
@@ -36,7 +36,7 @@ class ListLambdaPollHook(PollHook.PollHook):
 
 class Bot(object):
     def __init__(self, directory, args, cache, config, database, events,
-            exports, log, modules, timers):
+            exports, log, modules, timers, lock_file):
         self.directory = directory
         self.args = args
         self.cache = cache
@@ -71,6 +71,7 @@ class Bot(object):
         self._poll_timeouts = [] # typing.List[PollHook]
         self._poll_timeouts.append(self._timers)
         self._poll_timeouts.append(self.cache)
+        self._poll_timeouts.append(lock_file)
 
         self._poll_timeouts.append(ListLambdaPollHook(
             lambda: self.servers.values(),
diff --git a/src/LockFile.py b/src/LockFile.py
new file mode 100644
index 00000000..9f53b8d5
--- /dev/null
+++ b/src/LockFile.py
@@ -0,0 +1,40 @@
+import datetime, os
+from src import PollHook, utils
+
+EXPIRATION = 60 # 1 minute
+
+class LockFile(PollHook.PollHook):
+    def __init__(self, database_location: str):
+        self._database_location = database_location
+        self._lock_location = "%s.lock" % database_location
+        self._next_lock = None
+
+    def available(self):
+        now = utils.datetime_utcnow()
+        if os.path.exists(self._lock_location):
+            with open(self._lock_location, "r") as lock_file:
+                timestamp_str = lock_file.read().strip().split(" ", 1)[0]
+
+            timestamp = utils.iso8601_parse(timestamp_str)
+
+            if (now-timestamp).total_seconds() < EXPIRATION:
+                return False
+
+        return True
+
+    def lock(self):
+        with open(self._lock_location, "w") as lock_file:
+            last_lock = utils.datetime_utcnow()
+            lock_file.write("%s" % utils.iso8601_format(last_lock))
+            self._next_lock = last_lock+datetime.timedelta(
+                seconds=EXPIRATION/2)
+
+    def next(self):
+        return max(0, (self._next_lock-utils.datetime_utcnow()).total_seconds())
+    def call(self):
+        if self.next() == 0:
+            self.lock()
+
+    def unlock(self):
+        if os.path.isfile(self._lock_location):
+            os.remove(self._lock_location)
diff --git a/src/utils/__init__.py b/src/utils/__init__.py
index eaf3cc03..d36112a5 100644
--- a/src/utils/__init__.py
+++ b/src/utils/__init__.py
@@ -15,6 +15,9 @@ ISO8601_FORMAT_TZ = "%z"
 
 DATETIME_HUMAN = "%Y/%m/%d %H:%M:%S"
 
+def datetime_utcnow() -> datetime.datetime:
+    return datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc)
+
 def iso8601_format(dt: datetime.datetime, milliseconds: bool=False) -> str:
     dt_format = dt.strftime(ISO8601_FORMAT_DT)
     tz_format = dt.strftime(ISO8601_FORMAT_TZ)
@@ -25,8 +28,7 @@ def iso8601_format(dt: datetime.datetime, milliseconds: bool=False) -> str:
 
     return "%s%s%s" % (dt_format, ms_format, tz_format)
 def iso8601_format_now(milliseconds: bool=False) -> str:
-    now = datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc)
-    return iso8601_format(now, milliseconds=milliseconds)
+    return iso8601_format(datetime_utcnow(), milliseconds=milliseconds)
 def iso8601_parse(s: str, microseconds: bool=False) -> datetime.datetime:
     fmt = ISO8601_PARSE_MICROSECONDS if microseconds else ISO8601_PARSE
     return datetime.datetime.strptime(s, fmt)
diff --git a/start.py b/start.py
index 47b703ec..9c000521 100755
--- a/start.py
+++ b/start.py
@@ -6,9 +6,9 @@ if sys.version_info < (3, 6):
     sys.stderr.write("BitBot requires python 3.6.0 or later\n")
     sys.exit(1)
 
-import argparse, faulthandler, os, platform, time
+import atexit, argparse, faulthandler, os, platform, time
 from src import Cache, Config, Database, EventManager, Exports, IRCBot
-from src import Logging, ModuleManager, Timers, utils
+from src import LockFile, Logging, ModuleManager, Timers, utils
 
 faulthandler.enable()
 
@@ -65,6 +65,14 @@ log = Logging.Log(not args.no_logging, log_level, args.log_dir)
 log.info("Starting BitBot %s (Python v%s)",
     [IRCBot.VERSION, platform.python_version()])
 
+lock_file = LockFile.LockFile(args.database)
+if not lock_file.available():
+    log.critical("Database is locked. Is BitBot already running?")
+    sys.exit(1)
+
+atexit.register(lock_file.unlock)
+lock_file.lock()
+
 database = Database.Database(log, args.database)
 
 if args.remove_server:
@@ -98,7 +106,7 @@ modules = ModuleManager.ModuleManager(events, exports, timers, config, log,
     module_directories)
 
 bot = IRCBot.Bot(directory, args, cache, config, database, events,
-    exports, log, modules, timers)
+    exports, log, modules, timers, lock_file)
 
 if args.module:
     definition = modules.find_module(args.module)