initial 'signals-actions' implementation (#6582)

https://github.com/mikf/gallery-dl/issues/6582#issuecomment-2973285775

To stop gracefully after the current file finishes processing when
Ctrl+C was pressed, or after the current post finishes processing when
SIGUSR1 was received:

{
    "signals-actions": {
        "SIGINT" : "file",
        "SIGUSR1": "post"
    }
}

gallery_dl/__init__.py

@@ -11,7 +11,7 @@ import logging
 from . import version, config, option, output, extractor, job, util, exception
 
 __author__ = "Mike Fährmann"
-__copyright__ = "Copyright 2014-2023 Mike Fährmann"
+__copyright__ = "Copyright 2014-2025 Mike Fährmann"
 __license__ = "GPLv2"
 __maintainer__ = "Mike Fährmann"
 __email__ = "mike_faehrmann@web.de"
@@ -78,8 +78,7 @@ def main():
         output.configure_standard_streams()
 
         # signals
-        signals = config.get((), "signals-ignore")
+        if signals := config.get((), "signals-ignore"):
-        if signals:
             import signal
             if isinstance(signals, str):
                 signals = signals.split(",")
@@ -90,6 +89,19 @@ def main():
                 else:
                     signal.signal(signal_num, signal.SIG_IGN)
 
+        if signals := config.get((), "signals-actions"):
+            import signal
+            for signal_name, action in signals.items():
+                signal_num = getattr(signal, signal_name, None)
+                if signal_num is None:
+                    log.warning("signal '%s' is not defined", signal_name)
+                else:
+                    def handler(signal_num, frame):
+                        signal_name = signal.Signals(signal_num).name
+                        output.stderr_write(f"{signal_name} received\n")
+                        util.FLAGS.__dict__[action.upper()] = "stop"
+                    signal.signal(signal_num, handler)
+
         # enable ANSI escape sequences on Windows
         if util.WINDOWS and config.get(("output",), "ansi", output.COLORS):
             from ctypes import windll, wintypes, byref

gallery_dl/job.py

@@ -28,6 +28,7 @@ from . import (
 )
 from .extractor.message import Message
 stdout_write = output.stdout_write
+FLAGS = util.FLAGS
 
 
 class Job():
@@ -200,6 +201,8 @@ class Job():
             if self.pred_url(url, kwdict):
                 self.update_kwdict(kwdict)
                 self.handle_url(url, kwdict)
+            if FLAGS.FILE is not None:
+                FLAGS.FILE = FLAGS.process(FLAGS.FILE)
 
         elif msg[0] == Message.Directory:
             self.update_kwdict(msg[1])
@@ -212,6 +215,8 @@ class Job():
             if self.pred_queue(url, kwdict):
                 self.update_kwdict(kwdict)
                 self.handle_queue(url, kwdict)
+            if FLAGS.CHILD is not None:
+                FLAGS.CHILD = FLAGS.process(FLAGS.CHILD)
 
     def handle_url(self, url, kwdict):
         """Handle Message.Url"""
@@ -390,6 +395,8 @@ class DownloadJob(Job):
             if "post-after" in self.hooks:
                 for callback in self.hooks["post-after"]:
                     callback(self.pathfmt)
+            if FLAGS.POST is not None:
+                FLAGS.POST = FLAGS.process(FLAGS.POST)
             self.pathfmt.set_directory(kwdict)
         if "post" in self.hooks:
             for callback in self.hooks["post"]:

gallery_dl/util.py

@@ -722,6 +722,17 @@ class CustomNone():
     __repr__ = __str__
 
 
+class Flags():
+
+    def __init__(self):
+        self.FILE = self.POST = self.CHILD = self.DOWNLOAD = None
+
+    def process(self, flag):
+        if flag == "terminate":
+            raise exception.TerminateExtraction()
+        raise exception.StopExtraction()
+
+
 # v137.0 release of Firefox on 2025-04-01 has ordinal 739342
 # 735506 == 739342 - 137 * 28
 # v135.0 release of Chrome  on 2025-04-01 has ordinal 739342
@@ -737,6 +748,7 @@ re = text.re
 re_compile = text.re_compile
 
 NONE = CustomNone()
+FLAGS = Flags()
 EPOCH = datetime.datetime(1970, 1, 1)
 SECOND = datetime.timedelta(0, 1)
 WINDOWS = (os.name == "nt")