rewrite rate-limiter to not create any tasks

respodns/dns.py

@@ -284,7 +284,7 @@ async def read_all_ips(filepaths, blocking=False, callback=None):
 
 async def main(db, filepaths, checks, ipinfo, opts: Options):
     # ipinfo can be None.
-    from .util import LimitPerSecond
+    from .util import RateLimiter
     from asyncio import Queue, QueueFull, create_task
     from queue import SimpleQueue
 
@@ -292,7 +292,7 @@ async def main(db, filepaths, checks, ipinfo, opts: Options):
     locate_me = Queue()
     try_me = Queue()
     pps = opts.packets_per_second
-    context = LimitPerSecond(pps) if pps > 0 else None
+    context = RateLimiter(pps) if pps > 0 else None
 
     def locate_later(ip):
         try:
@@ -335,6 +335,3 @@ async def main(db, filepaths, checks, ipinfo, opts: Options):
 
     await locate_me.put(None)
     await locating
-
-    if context is not None and hasattr(context, "finish"):
-        await context.finish()

respodns/util.py

@@ -58,37 +58,39 @@ class AttrCheck:
             raise AttributeError(name)
 
 
-async def _release_later(sem, time=1):
-    from asyncio import sleep
-
-    await sleep(time)
-    sem.release()
+def _present():
+    from time import time
+    return time()
 
 
-class LimitPerSecond:
+class RateLimiter:
     def __init__(self, limit):
-        from asyncio import BoundedSemaphore
+        from asyncio import Lock
 
         if type(limit) is not int:
             raise ValueError("limit must be int")
         assert limit > 0, limit
 
+        self.unit = 1.0  # TODO: allow window length to be configured.
         self.limit = limit
-        self.tasks = []
-        self.sem = BoundedSemaphore(limit)
+        self.times = []
+        self.lock = Lock()
+        self.eps = self.unit * 0.01  # to wait a tiny bit longer than specified
+
+    def eta(self):
+        past = _present() - self.unit
+        self.times = [time for time in self.times if time > past]
+        ind = len(self.times) - self.limit
+        return 0.0 if ind < 0 else self.times[ind] - past
 
     async def __aenter__(self):
-        #if self.sem.locked:
-        #    from sys import stderr
-        #    print("THROTTLING", file=stderr)
-        await self.sem.acquire()
+        from asyncio import sleep
+
+        async with self.lock:
+            while (wait := self.eta()) > 0.0:
+                # this is done in a loop in case sleep ends early (it can).
+                await sleep(wait + self.eps)
+            self.times.append(_present())
 
     async def __aexit__(self, exc_type, exc_value, traceback):
-        from asyncio import create_task
-
-        task = create_task(_release_later(self.sem))
-        self.tasks.append(task)
-
-    async def finish(self):
-        for task in self.tasks:
-            await task
+        pass