fix: recent asyncio change resulting in sequential downloads

This was due to AsyncIO completely ignoring the thread (size) argument, and not updating sleep to be non-blocking.

nhentai/command.py

@@ -77,7 +77,7 @@ def main():
         doujinshi_ids = list(set(map(int, doujinshi_ids)) - set(data))
 
     if not options.is_show:
-        downloader = Downloader(path=options.output_dir, size=options.threads,
+        downloader = Downloader(path=options.output_dir, threads=options.threads,
                                 timeout=options.timeout, delay=options.delay)
 
         for doujinshi_id in doujinshi_ids:

nhentai/downloader.py

@@ -1,9 +1,6 @@
 # coding: utf-
 
-import multiprocessing
-
 import os
-import time
 import urllib3.exceptions
 
 from urllib.parse import urlparse
@@ -15,8 +12,6 @@ import asyncio
 import httpx
 
 urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)
-semaphore = multiprocessing.Semaphore(1)
-
 
 class NHentaiImageNotExistException(Exception):
     pass
@@ -38,16 +33,23 @@ def download_callback(result):
 
 
 class Downloader(Singleton):
-    def __init__(self, path='', size=5, timeout=30, delay=0):
-        self.size = size
+    def __init__(self, path='', threads=5, timeout=30, delay=0):
+        self.semaphore = asyncio.Semaphore(threads)
         self.path = str(path)
         self.timeout = timeout
         self.delay = delay
 
+    async def _semaphore_download(self, *args, **kwargs):
+        # This sets a concurrency limit for AsyncIO
+        async with self.semaphore:
+            return await self.download(*args, **kwargs)
+
     async def download(self, url, folder='', filename='', retried=0, proxy=None):
-        if self.delay:
-            time.sleep(self.delay)
         logger.info(f'Starting to download {url} ...')
+
+        if self.delay:
+            await asyncio.sleep(self.delay)
+
         filename = filename if filename else os.path.basename(urlparse(url).path)
 
         save_file_path = os.path.join(self.folder, filename)
@@ -150,7 +152,7 @@ class Downloader(Singleton):
                     logger.error(f'An error occurred: {e}')
 
         tasks = [
-            self.download(url, filename=os.path.basename(urlparse(url).path))
+            self._semaphore_download(url, filename=os.path.basename(urlparse(url).path))
             for url in queue
         ]
         # Prevent coroutines infection