Add tests for thread safety.

test/runtests.jl

@@ -10,4 +10,5 @@ include("convert.jl")
 include("macros.jl")
 include("packages.jl")
 include("help.jl")
+include("sync.jl")
 # include("testmanual.jl")  # leave this out until doctestfilters can be used here

test/sync.jl

@@ -0,0 +1,36 @@
+function run_timed(script :: String, timeout :: Int)
+  cmd = Cmd(Base.julia_cmd();
+    env = merge(ENV, Dict("JULIA_NUM_THREADS" => "2")))
+  push!(cmd.exec, "-e", script)
+  process = open(cmd)
+  task = @async begin
+    wait(process)
+  end
+  for t in 1:(timeout*10)
+    sleep(0.1)
+    if task.state == :done
+      return process.exitcode == 0
+    end
+  end
+  kill(process, 9)
+  return false
+end
+
+@testset "sync" begin
+  @test run_timed("""
+  using GAP
+  Threads.@threads for i = 1:20000
+    GAP.Globals.SymmetricGroup(7)
+  end
+  """, 10)
+  @test run_timed("""
+  using GAP
+  function test()
+    perm = @gap "()"
+    Threads.@threads for i = 1:2000
+      perm *= GAP.evalstr("(\$(i), \$(i+1))")
+    end
+  end
+  test()
+  """, 10)
+end