Nospecialize ::Channel functions that don't depend on {T}.

- Mark most of the functions on Channels nospecialize when they don't
  depend on the data type in the Channel, `T`.
- Add precompile statement for `Base.close(::Channel, ::Exception)`

Author: NHDaly

base/channels.jl

@@ -183,8 +183,8 @@ Close a channel. An exception (optionally given by `excp`), is thrown by:
 * [`put!`](@ref) on a closed channel.
 * [`take!`](@ref) and [`fetch`](@ref) on an empty, closed channel.
 """
-close(c::Channel) = close(c, closed_exception()) # nospecialize on default arg seems to confuse makedocs
-function close(c::Channel, @nospecialize(excp::Exception))
+close(@nospecialize(c::Channel)) = close(c, closed_exception()) # nospecialize on default arg seems to confuse makedocs
+@nospecialize function close(c::Channel, excp::Exception)
     lock(c)
     try
         c.excp = excp
@@ -197,7 +197,7 @@ function close(c::Channel, @nospecialize(excp::Exception))
     end
     nothing
 end
-isopen(c::Channel) = ((@atomic :monotonic c.state) === :open)
+@nospecialize isopen(c::Channel) = ((@atomic :monotonic c.state) === :open)
 
 """
     bind(chnl::Channel, task::Task)

contrib/generate_precompile.jl

@@ -49,6 +49,7 @@ precompile(Tuple{typeof(isassigned), Core.SimpleVector, Int})
 precompile(Tuple{typeof(getindex), Core.SimpleVector, Int})
 precompile(Tuple{typeof(Base.Experimental.register_error_hint), Any, Type})
 precompile(Tuple{typeof(Base.display_error), Base.ExceptionStack})
+precompile(Tuple{typeof(Base.close), Base.Channel, Exception})
 precompile(Tuple{Core.kwftype(typeof(Type)), NamedTuple{(:sizehint,), Tuple{Int}}, Type{IOBuffer}})
 precompile(Base.CoreLogging.current_logger_for_env, (Base.CoreLogging.LogLevel, String, Module))
 precompile(Base.CoreLogging.current_logger_for_env, (Base.CoreLogging.LogLevel, Symbol, Module))