Allow CapacityLimiter(math.inf)

newsfragments/618.feature.rst

@@ -0,0 +1 @@
+You can now create an unbounded :class:`CapacityLimiter` by initializing with :obj:`math.inf`

trio/_sync.py

@@ -1,5 +1,6 @@
 import operator
 from collections import deque, OrderedDict
+import math
 
 import attr
 import outcome
@@ -199,8 +200,10 @@ def total_tokens(self):
 
     @total_tokens.setter
     def total_tokens(self, new_total_tokens):
-        if not isinstance(new_total_tokens, int):
-            raise TypeError("total_tokens must be an int")
+        if not isinstance(
+            new_total_tokens, int
+        ) and new_total_tokens != math.inf:
+            raise TypeError("total_tokens must be an int or math.inf")
         if new_total_tokens < 1:
             raise ValueError("total_tokens must be >= 1")
         self._total_tokens = new_total_tokens

trio/_wait_for_object.py

@@ -1,19 +1,13 @@
+import math
 from . import _timeouts
 from . import _core
 from ._threads import run_sync_in_worker_thread
 from ._core._windows_cffi import ffi, kernel32, ErrorCodes, raise_winerror, _handle
+from ._sync import CapacityLimiter
 
 __all__ = ["WaitForSingleObject"]
 
 
-class StubLimiter:
-    def release_on_behalf_of(self, x):
-        pass
-
-    async def acquire_on_behalf_of(self, x):
-        pass
-
-
 async def WaitForSingleObject(obj):
     """Async and cancellable variant of WaitForSingleObject. Windows only.
 
@@ -45,7 +39,7 @@ async def WaitForSingleObject(obj):
             handle,
             cancel_handle,
             cancellable=True,
-            limiter=StubLimiter(),
+            limiter=CapacityLimiter(math.inf),
         )
     finally:
         # Clean up our cancel handle. In case we get here because this task was

trio/tests/test_sync.py

@@ -115,6 +115,21 @@ async def test_CapacityLimiter():
     c.release_on_behalf_of("value 1")
 
 
+async def test_CapacityLimiter_inf():
+    from math import inf
+    c = CapacityLimiter(inf)
+    repr(c)  # smoke test
+    assert c.total_tokens == inf
+    assert c.borrowed_tokens == 0
+    assert c.available_tokens == inf
+    with pytest.raises(RuntimeError):
+        c.release()
+    assert c.borrowed_tokens == 0
+    c.acquire_nowait()
+    assert c.borrowed_tokens == 1
+    assert c.available_tokens == inf
+
+
 async def test_CapacityLimiter_change_total_tokens():
     c = CapacityLimiter(2)