1 files changed, 93 insertions, 0 deletions
diff --git a/coroutine/asyncify/Context.h b/coroutine/asyncify/Context.h
new file mode 100644
index 0000000000..71791a4004
--- /dev/null
+++ b/coroutine/asyncify/Context.h
@@ -0,0 +1,93 @@
+#ifndef COROUTINE_ASYNCIFY_CONTEXT_H
+#define COROUTINE_ASYNCIFY_CONTEXT_H
+
+/*
+ This is a coroutine implementation based on Binaryen's Asyncify transformation for WebAssembly.
+
+ This implementation is built on low-level ucontext-like API in wasm/fiber.c
+ This file is an adapter for the common coroutine interface and for stack manipulation.
+ wasm/fiber.c doesn't take care of stack to avoid duplicate management with this adapter.
+
+ * See also: wasm/fiber.c
+*/
+
+#include <stddef.h>
+#include <stdio.h>
+#include <stdint.h>
+#include "wasm/asyncify.h"
+#include "wasm/machine.h"
+#include "wasm/fiber.h"
+
+#define COROUTINE void __attribute__((__noreturn__))
+
+static const int ASYNCIFY_CORO_DEBUG = 0;
+
+struct coroutine_context
+{
+    rb_wasm_fiber_context fc;
+    void *argument;
+    struct coroutine_context *from;
+
+    void *current_sp;
+    void *stack_base;
+    size_t size;
+};
+
+typedef COROUTINE(* coroutine_start)(struct coroutine_context *from, struct coroutine_context *self);
+
+COROUTINE coroutine_trampoline(void * _start, void * _context);
+
+static inline void coroutine_initialize_main(struct coroutine_context * context)
+{
+    if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p)\n", __func__, context);
+    // NULL fiber entry means it's the main fiber, and handled specially.
+    rb_wasm_init_context(&context->fc, NULL, NULL, NULL);
+    // mark the main fiber has already started
+    context->fc.is_started = true;
+}
+
+static inline void coroutine_initialize(struct coroutine_context *context, coroutine_start start, void *stack, size_t size)
+{
+    // Linear stack pointer must be always aligned down to 16 bytes.
+    // https://github.com/WebAssembly/tool-conventions/blob/c74267a5897c1bdc9aa60adeaf41816387d3cd12/BasicCABI.md#the-linear-stack
+    uintptr_t sp = ((uintptr_t)stack + size) & ~0xF;
+    if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p, stack = %p ... %p)\n", __func__, context, stack, (char *)sp);
+    rb_wasm_init_context(&context->fc, coroutine_trampoline, start, context);
+    // record the initial stack pointer position to restore it after resumption
+    context->current_sp = (char *)sp;
+    context->stack_base = stack;
+    context->size = size;
+}
+
+static inline struct coroutine_context * coroutine_transfer(struct coroutine_context * current, struct coroutine_context * target)
+{
+    if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (current = %p, target = %p)\n", __func__, current, target);
+    struct coroutine_context * previous = target->from;
+
+    target->from = current;
+    if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] current->current_sp = %p -> %p\n", __func__, current->current_sp, rb_wasm_get_stack_pointer());
+    // record the current stack pointer position to restore it after resumption
+    current->current_sp = rb_wasm_get_stack_pointer();
+
+    // suspend the current coroutine and resume another coroutine
+
+    rb_wasm_swapcontext(&current->fc, &target->fc);
+
+    // after the original coroutine resumed
+
+    rb_wasm_set_stack_pointer(current->current_sp);
+
+    target->from = previous;
+
+    return target;
+}
+
+static inline void coroutine_destroy(struct coroutine_context * context)
+{
+    if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p)\n", __func__, context);
+    context->stack_base = NULL;
+    context->size = 0;
+    context->from = NULL;
+}
+
+#endif /* COROUTINE_ASYNCIFY_CONTEXT_H */