The 0.15.2 version, using httpclient, using --threads:on compile time error:
import httpclient, threadpool
proc test() {.gcsafe.} =
var client = newHttpClient()
var data = newMultipartData()
data["output"] = "soap12"
data["uploaded_file"] = ("test.html", "text/html",
"<html><head></head><body><p>test</p></body></html>")
echo client.postContent("http://validator.w3.org/check", multipart=data)
spawn test()
a.nim(3, 6) Error: 'test' is not GC-safe as it accesses 'defaultSSLContext' which is a global using GC'ed memory