Initial project import

tools/v/vlib/goroutines/context_windows.c.v

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+// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+//
+// Platform-specific context switching using Windows Fibers.
+module goroutines
+
+#include <windows.h>
+
+fn C.CreateFiber(dwStackSize usize, lpStartAddress voidptr, lpParameter voidptr) voidptr
+fn C.ConvertThreadToFiber(lpParameter voidptr) voidptr
+fn C.SwitchToFiber(lpFiber voidptr)
+fn C.DeleteFiber(lpFiber voidptr)
+fn C.ConvertFiberToThread()
+
+pub struct Context {
+pub mut:
+	uctx            voidptr // fiber handle on Windows
+	is_thread_fiber bool    // true if this was created via ConvertThreadToFiber
+}
+
+pub fn context_init(mut ctx Context, stack voidptr, stack_size int, entry_fn fn (voidptr), arg voidptr) {
+	// Windows fibers manage their own stack, so we ignore the stack param
+	ctx.uctx = C.CreateFiber(usize(stack_size), voidptr(entry_fn), arg)
+}
+
+pub fn context_switch(mut from Context, to &Context) {
+	C.SwitchToFiber(to.uctx)
+}
+
+pub fn context_set(to &Context) {
+	C.SwitchToFiber(to.uctx)
+}
+
+// convert_thread_to_fiber must be called once per OS thread before using fibers.
+pub fn convert_thread_to_fiber() Context {
+	mut ctx := Context{}
+	ctx.uctx = C.ConvertThreadToFiber(unsafe { nil })
+	ctx.is_thread_fiber = true
+	return ctx
+}