fix heartbeat on 1.6 (#985)

Author: stevengj

Project.toml

@@ -8,6 +8,7 @@ Conda = "8f4d0f93-b110-5947-807f-2305c1781a2d"
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 JSON = "682c06a0-de6a-54ab-a142-c8b1cf79cde6"
+Libdl = "8f399da3-3557-5675-b5ff-fb832c97cbdb"
 Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"
 MbedTLS = "739be429-bea8-5141-9913-cc70e7f3736d"
 Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"

src/heartbeat.jl

@@ -4,18 +4,20 @@
 # call in libzmq, which simply blocks forever, so the usual lack of
 # thread safety in Julia should not be an issue here.
 
+import Libdl
 
 const threadid = zeros(Int, 128) # sizeof(uv_thread_t) <= 8 on Linux, OSX, Win
-using ZMQ: libzmq
+const zmq_proxy = Ref(C_NULL)
 
 # entry point for new thread
 function heartbeat_thread(sock::Ptr{Cvoid})
-    ccall((:zmq_proxy,libzmq), Cint, (Ptr{Cvoid}, Ptr{Cvoid}, Ptr{Cvoid}),
+    ccall(zmq_proxy[], Cint, (Ptr{Cvoid}, Ptr{Cvoid}, Ptr{Cvoid}),
           sock, sock, C_NULL)
     nothing
 end
 
 function start_heartbeat(sock)
+    zmq_proxy[] = Libdl.dlsym(Libdl.dlopen(ZMQ.libzmq), :zmq_proxy)
     heartbeat_c = @cfunction(heartbeat_thread, Cvoid, (Ptr{Cvoid},))
     ccall(:uv_thread_create, Cint, (Ptr{Int}, Ptr{Cvoid}, Ptr{Cvoid}),
           threadid, heartbeat_c, sock)