allow port reuse on HTTP end

This will allow multiple HTTP servers to be multiplexed on the same port on the HTTP end.
This is useful to bypass the limitation in Julia where a `ccall` blocks all tasks in the process.
With this change multiple HTTP clients can get requests serviced simultaneously using more than one servers.
The HTTP ends can further talk to one or more backends as needed.

src/http_rpc_server.jl

@@ -202,6 +202,22 @@ immutable HttpRpcServer{T,F}
     server::Server
 end
 
+function reusable_tcpserver()
+    tcp = Base.TCPServer(Base.Libc.malloc(Base._sizeof_uv_tcp), Base.StatusUninit)
+    err = ccall(:uv_tcp_init_ex, Cint, (Ptr{Void}, Ptr{Void}, Cuint),
+                Base.eventloop(), tcp.handle, 2)
+    Base.uv_error("failed to create tcp server", err)
+    tcp.status = Base.StatusInit
+
+    rc = ccall(:jl_tcp_reuseport, Int32, (Ptr{Void},), tcp.handle)
+    if rc == 0
+        Logging.info("Reusing TCP port")
+    else
+        Logging.warn("Unable to reuse TCP port, error:", rc)
+    end
+    return tcp
+end
+
 HttpRpcServer{T,F}(api::APIInvoker{T,F}, preproc::Function=default_preproc) = HttpRpcServer([api], preproc)
 function HttpRpcServer{T,F}(apis::Vector{APIInvoker{T,F}}, preproc::Function=default_preproc)
     api = Channel{APIInvoker{T,F}}(length(apis))
@@ -213,7 +229,7 @@ function HttpRpcServer{T,F}(apis::Vector{APIInvoker{T,F}}, preproc::Function=def
         return http_handler(api, preproc, req, res)
     end
 
-    handler = HttpHandler(handler)
+    handler = HttpHandler(handler, reusable_tcpserver())
     handler.events["error"] = on_error
     handler.events["listen"] = on_listen
     server = Server(handler)

test/clnt.jl

@@ -6,6 +6,7 @@ using Logging
 using ZMQ
 using Base.Test
 using Requests
+using JSON
 
 Logging.configure(level=INFO)
 

test/srvr.jl

@@ -6,6 +6,7 @@ using HttpCommon
 using Logging
 using Compat
 using ZMQ
+using JSON
 
 include("srvrfn.jl")