fix throttling

The old implementation will wait for all of the last max_concurrent ones
to complete.

nvchecker/core.py

@@ -122,40 +122,43 @@ class Source:
       self.oldvers = {}
     self.curvers = self.oldvers.copy()
 
-    futures = set()
+    token_q = asyncio.Queue(maxsize=self.max_concurrent)
+
+    async def worker(name, conf):
+      await token_q.get()
+      ret = await get_version(name, conf)
+      return name, ret
+
+    async def token_filler(n):
+      for _ in range(n):
+        await token_q.put(True)
+
     config = self.config
+    futures = []
     for name in config.sections():
       if name == '__config__':
         continue
+
       conf = config[name]
       conf['oldver'] = self.oldvers.get(name, None)
-      fu = asyncio.ensure_future(get_version(name, conf))
-      fu.name = name
-      futures.add(fu)
+      fu = asyncio.ensure_future(worker(name, conf))
+      futures.append(fu)
 
-      if len(futures) >= self.max_concurrent:
-        (done, futures) = await asyncio.wait(
-          futures, return_when = asyncio.FIRST_COMPLETED)
-        for fu in done:
-          self.future_done(fu)
+    filler_fu = asyncio.ensure_future(token_filler(len(futures)))
 
-    if futures:
-      (done, _) = await asyncio.wait(futures)
-      for fu in done:
-        self.future_done(fu)
+    for fu in asyncio.as_completed(futures):
+      try:
+        name, version = await fu
+        if version is not None:
+          self.print_version_update(name, version)
+      except Exception:
+        logger.exception('unexpected error happened', name=name)
+
+    await filler_fu
 
     if self.newver:
       write_verfile(self.newver, self.curvers)
 
-  def future_done(self, fu):
-    name = fu.name
-    try:
-      version = fu.result()
-      if version is not None:
-        self.print_version_update(name, version)
-    except Exception:
-      logger.exception('unexpected error happened', name=name)
-
   def print_version_update(self, name, version):
     oldver = self.oldvers.get(name, None)
     if not oldver or oldver != version: