Disable multithreading in Windows due instability

Author: mkitti

src/JNI.jl

@@ -16,6 +16,7 @@ export JNI_VERSION_1_1, JNI_VERSION_1_2, JNI_VERSION_1_4, JNI_VERSION_1_6, JNI_V
 export JNI_OK, JNI_ERR, JNI_EDETACHED, JNI_EVERSION, JNI_ENOMEM, JNI_EEXIST, JNI_EINV
 #export jnifunc
 
+include("Threads.jl")
 include("jnienv.jl")
 
 const jniref = Ref(JNINativeInterface())

src/JavaCall.jl

@@ -33,6 +33,7 @@ JULIA_COPY_STACKS = false
 
 include("JNI.jl")
 using .JNI
+import .JNI.Threads
 include("jvm.jl")
 include("core.jl")
 include("convert.jl")

src/Threads.jl

@@ -0,0 +1,20 @@
+"""
+    JavaCall.JNI.Threads is a standin module for Base.Threads
+
+    On Windows, it disables multithreading for JavaCall since JavaCall becomes
+    unstable in Windows.
+
+    On other operating systems, it just uses Base.Threads.
+"""
+module Threads
+    @static if Sys.iswindows()
+        threadid() = 1
+        nthreads() = 1
+        resize_nthreads!(x) = x
+        macro threads(expr)
+            esc(expr)
+        end
+    else
+        import Base.Threads: resize_nthreads!, @threads, threadid, nthreads
+    end
+end

src/jvm.jl

@@ -226,11 +226,16 @@ const ROOT_TASK_ERROR = JavaCallError(
 const JULIA_COPY_STACKS_ON_WINDOWS_ERROR = JavaCallError(
     "JULIA_COPY_STACKS should not be set on Windows.")
 
+const THREADID_NOT_ONE_WINDOWS_ERROR = JavaCallError(
+    "JavaCall must be used on Thread 1 only in Windows. Multithreading JavaCall is not supported on Windows."
+)
+
 # JavaCall must run on the root Task or JULIA_COPY_STACKS is enabled
 isroottask() = Base.roottask === Base.current_task()
 @static if Sys.iswindows()
-    isgoodenv() = ! JULIA_COPY_STACKS
-    assertroottask_or_goodenv() = isgoodenv() ? true : throw(JULIA_COPY_STACKS_ON_WINDOWS_ERROR)
+    isgoodenv() = ( ! JULIA_COPY_STACKS ) && Base.Threads.threadid() == 1
+    assertroottask_or_goodenv() = isgoodenv() ? true : Base.Threads.threadid() == 1 ?
+        throw(JULIA_COPY_STACKS_ON_WINDOWS_ERROR) : throw(THREADID_NOT_ONE_WINDOWS_ERROR)
 else
     isgoodenv() = JULIA_COPY_STACKS || isroottask()
     assertroottask_or_goodenv() = isgoodenv() ? true : throw(ROOT_TASK_ERROR)