Implement async callback test on Windows and improve async specs

spec/ffi/async_callback_spec.rb

@@ -19,19 +19,24 @@ module LibTest
     skip "not yet supported on TruffleRuby" if RUBY_ENGINE == "truffleruby"
     v = 0xdeadbeef
     called = false
-    cb = Proc.new {|i| v = i; called = true }
+    cb = Proc.new {|i| v = i; called = Thread.current }
     LibTest.testAsyncCallback(cb, 0x7fffffff)
-    expect(called).to be true
+    expect(called).to be_kind_of(Thread)
+    expect(called).to_not eq(Thread.current)
     expect(v).to eq(0x7fffffff)
   end
 
   it "called a second time" do
     skip "not yet supported on TruffleRuby" if RUBY_ENGINE == "truffleruby"
-    v = 0xdeadbeef
-    called = false
-    cb = Proc.new {|i| v = i; called = true }
-    LibTest.testAsyncCallback(cb, 0x7fffffff)
-    expect(called).to be true
-    expect(v).to eq(0x7fffffff)
+    v = 1
+    th1 = th2 = false
+    LibTest.testAsyncCallback(2) { |i| v += i; th1 = Thread.current }
+    LibTest.testAsyncCallback(3) { |i| v += i; th2 = Thread.current }
+    expect(th1).to be_kind_of(Thread)
+    expect(th2).to be_kind_of(Thread)
+    expect(th1).to_not eq(Thread.current)
+    expect(th2).to_not eq(Thread.current)
+    expect(th1).to_not eq(th2)
+    expect(v).to eq(6)
   end
 end

spec/ffi/fixtures/FunctionTest.c

@@ -6,6 +6,7 @@
 
 #ifdef _WIN32
 #include <windows.h>
+#include <process.h>
 #endif
 
 #ifndef _WIN32
@@ -115,17 +116,26 @@ static void* asyncThreadCall(void *data)
     return NULL;
 }
 
+#ifdef _WIN32
+static void
+asyncThreadCall_win32(void *arg)
+{
+    asyncThreadCall(arg);
+}
+#endif
+
 void testAsyncCallback(void (*fn)(int), int value)
 {
-#ifndef _WIN32
-    pthread_t t;
     struct async_data d;
     d.fn = fn;
     d.value = value;
+#ifndef _WIN32
+    pthread_t t;
     pthread_create(&t, NULL, asyncThreadCall, &d);
     pthread_join(t, NULL);
 #else
-    (*fn)(value);
+    HANDLE hThread = (HANDLE) _beginthread(asyncThreadCall_win32, 0, &d);
+    WaitForSingleObject(hThread, INFINITE);
 #endif
 }