chore(async): add Channel (#1456)

lua/mason-core/async/control.lua

@@ -15,9 +15,14 @@ function Condvar:wait()
     end)
 end
 
+function Condvar:notify()
+    local handle = table.remove(self.handles)
+    pcall(handle)
+end
+
 function Condvar:notify_all()
-    for _, handle in ipairs(self.handles) do
-        pcall(handle)
+    while #self.handles > 0 do
+        self:notify()
     end
     self.handles = {}
 end
@@ -97,8 +102,61 @@ function OneShotChannel:receive()
     return unpack(self.value)
 end
 
+---@class Channel
+---@field private condvar Condvar
+---@field private buffer any?
+---@field is_closed boolean
+local Channel = {}
+Channel.__index = Channel
+function Channel.new()
+    return setmetatable({
+        condvar = Condvar.new(),
+        buffer = nil,
+        is_closed = false,
+    }, Channel)
+end
+
+function Channel:close()
+    self.is_closed = true
+end
+
+---@async
+function Channel:send(value)
+    assert(not self.is_closed, "Channel is closed.")
+    while self.buffer ~= nil do
+        self.condvar:wait()
+    end
+    self.buffer = value
+    self.condvar:notify()
+    while self.buffer ~= nil do
+        self.condvar:wait()
+    end
+end
+
+---@async
+function Channel:receive()
+    assert(not self.is_closed, "Channel is closed.")
+    while self.buffer == nil do
+        self.condvar:wait()
+    end
+    local value = self.buffer
+    self.buffer = nil
+    self.condvar:notify()
+    return value
+end
+
+---@async
+function Channel:iter()
+    return function()
+        while not self.is_closed do
+            return self:receive()
+        end
+    end
+end
+
 return {
     Condvar = Condvar,
     Semaphore = Semaphore,
     OneShotChannel = OneShotChannel,
+    Channel = Channel,
 }

tests/mason-core/async/async_spec.lua

@@ -311,3 +311,58 @@ describe("async :: OneShotChannel", function()
         assert.equals(42, channel:receive())
     end)
 end)
+
+describe("async :: Channel", function()
+    local Channel = control.Channel
+
+    it("should suspend send until buffer is received", function()
+        local channel = Channel.new()
+        spy.on(channel, "send")
+        local guard = spy.new()
+
+        a.run(function()
+            channel:send "message"
+            guard()
+            channel:send "another message"
+        end, function() end)
+
+        assert.spy(channel.send).was_called(1)
+        assert.spy(channel.send).was_called_with(match.is_ref(channel), "message")
+        assert.spy(guard).was_not_called()
+    end)
+
+    it("should send subsequent messages after they're received", function()
+        local channel = Channel.new()
+        spy.on(channel, "send")
+
+        a.run(function()
+            channel:send "message"
+            channel:send "another message"
+        end, function() end)
+
+        local value = channel:receive()
+        assert.equals(value, "message")
+
+        assert.spy(channel.send).was_called(2)
+        assert.spy(channel.send).was_called_with(match.is_ref(channel), "message")
+        assert.spy(channel.send).was_called_with(match.is_ref(channel), "another message")
+    end)
+
+    it("should suspend receive until message is sent", function()
+        local channel = Channel.new()
+
+        a.run(function()
+            a.sleep(100)
+            channel:send "hello world"
+        end, function() end)
+
+        local start = timestamp()
+        local value = a.run_blocking(function()
+            return channel:receive()
+        end)
+        local stop = timestamp()
+
+        assert.is_true((stop - start) > 80)
+        assert.equals(value, "hello world")
+    end)
+end)