From 045cd60a12b4371a06be21c9a3eb53520c6b587c Mon Sep 17 00:00:00 2001
From: "Nathaniel J. Smith" <njs@pobox.com>
Date: Mon, 30 Jul 2018 01:47:03 -0700
Subject: [PATCH] Add trio.open_channel

---
 trio/__init__.py |   3 +
 trio/_channel.py | 202 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 205 insertions(+)
 create mode 100644 trio/_channel.py

diff --git a/trio/__init__.py b/trio/__init__.py
index 7ea2df21eb..acdc383b24 100644
--- a/trio/__init__.py
+++ b/trio/__init__.py
@@ -23,6 +23,9 @@
 from ._sync import *
 __all__ += _sync.__all__
 
+from ._channel import *
+__all__ += _channel.__all__
+
 from ._threads import *
 __all__ += _threads.__all__
 
diff --git a/trio/_channel.py b/trio/_channel.py
new file mode 100644
index 0000000000..bb2995516b
--- /dev/null
+++ b/trio/_channel.py
@@ -0,0 +1,202 @@
+from collections import deque, OrderedDict
+from math import inf
+
+import attr
+from outcome import Error, Value
+
+from . import _core
+from ._util import aiter_compat
+
+__all__ = ["open_channel", "EndOfChannel", "BrokenChannelError"]
+
+# TODO:
+# - introspection:
+#   - statistics
+#   - capacity, usage
+#   - repr
+# - BrokenResourceError?
+# - tests
+# - docs
+
+
+class EndOfChannel(Exception):
+    pass
+
+
+class BrokenChannelError(Exception):
+    pass
+
+
+def open_channel(capacity):
+    if capacity != inf and not isinstance(capacity, int):
+        raise TypeError("capacity must be an integer or math.inf")
+    if capacity < 0:
+        raise ValueError("capacity must be >= 0")
+    buf = ChannelBuf(capacity)
+    return PutChannel(buf), GetChannel(buf)
+
+
+@attr.s(cmp=False, hash=False)
+class ChannelBuf:
+    capacity = attr.ib()
+    data = attr.ib(default=attr.Factory(deque))
+    # counts
+    put_channels = attr.ib(default=0)
+    get_channels = attr.ib(default=0)
+    # {task: value}
+    put_tasks = attr.ib(default=attr.Factory(OrderedDict))
+    # {task: None}
+    get_tasks = attr.ib(default=attr.Factory(OrderedDict))
+
+
+class PutChannel:
+    def __init__(self, buf):
+        self._buf = buf
+        self.closed = False
+        self._tasks = set()
+        self._buf.put_channels += 1
+
+    @_core.disable_ki_protection
+    def put_nowait(self, value):
+        if self.closed:
+            raise _core.ClosedResourceError
+        if not self._buf.get_channels:
+            raise BrokenChannelError
+        if self._buf.get_tasks:
+            assert not self._buf.data
+            task = next(iter(self._buf.get_tasks))
+            _core.reschedule(task, Value(value))
+        elif len(self._buf.data) < self._buf.capacity:
+            self._buf.data.append(value)
+        else:
+            raise _core.WouldBlock
+
+    @_core.disable_ki_protection
+    async def put(self, value):
+        await _core.checkpoint_if_cancelled()
+        try:
+            self.put_nowait(value)
+        except _core.WouldBlock:
+            pass
+        else:
+            await _core.cancel_shielded_checkpoint()
+            return
+
+        task = _core.current_task()
+        self._tasks.add(task)
+        self._buf.put_tasks[task] = value
+
+        def abort_fn(_):
+            self._tasks.remove(task)
+            del self._buf.put_tasks[task]
+            return _core.Abort.SUCCEEDED
+
+        await _core.wait_task_rescheduled(abort_fn, always_abort=True)
+
+    @_core.disable_ki_protection
+    def clone(self):
+        if self.closed:
+            raise _core.ClosedResourceError
+        return PutChannel(self._buf)
+
+    @_core.disable_ki_protection
+    def close(self):
+        if self.closed:
+            return
+        self.closed = True
+        for task in list(self._tasks):
+            _core.reschedule(task, Error(ClosedResourceError()))
+        self._buf.put_channels -= 1
+        if self._buf.put_channels == 0:
+            assert not self._buf.put_tasks
+            for task in list(self._buf.get_tasks):
+                _core.reschedule(task, Error(EndOfChannel()))
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+class GetChannel:
+    def __init__(self, buf):
+        self._buf = buf
+        self.closed = False
+        self._tasks = set()
+        self._buf.get_channels += 1
+
+    @_core.disable_ki_protection
+    def get_nowait(self):
+        if self.closed:
+            raise _core.ClosedResourceError
+        buf = self._buf
+        if buf.put_tasks:
+            task, value = next(iter(buf.put_tasks.items()))
+            _core.reschedule(task)
+            return value
+        if buf.data:
+            return buf.data.popleft()
+        if not buf.put_channels:
+            raise EndOfChannel
+        raise _core.WouldBlock
+
+    @_core.disable_ki_protection
+    async def get(self):
+        await _core.checkpoint_if_cancelled()
+        try:
+            return self.get_nowait()
+        except _core.WouldBlock:
+            pass
+        else:
+            await _core.cancel_shielded_checkpoint()
+            return
+
+        task = _core.current_task()
+        self._tasks.add(task)
+        self._buf.get_tasks[task] = None
+
+        def abort_fn(_):
+            self._tasks.remove(task)
+            del self._buf.get_tasks[task]
+            return _core.Abort.SUCCEEDED
+
+        return await _core.wait_task_rescheduled(abort_fn, always_abort=True)
+
+    @_core.disable_ki_protection
+    def clone(self):
+        if self.closed:
+            raise _core.ClosedResourceError
+        return GetChannel(self._buf)
+
+    @_core.disable_ki_protection
+    def close(self):
+        if self.closed:
+            return
+        self.closed = True
+        for task in list(self._tasks):
+            _core.reschedule(task, Error(ClosedResourceError()))
+        self._buf.get_channels -= 1
+        if self._buf.get_channels == 0:
+            assert not self._buf.get_tasks
+            for task in list(self._buf.put_tasks):
+                _core.reschedule(task, Error(BrokenChannelError()))
+            # XX: or if we're losing data, maybe we should raise a
+            # BrokenChannelError here?
+            self._buf.data.clear()
+
+    @aiter_compat
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        try:
+            return await self.get()
+        except EndOfChannel:
+            raise StopAsyncIteration
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()