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#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 "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)
{
if (ASYNCIFY_CORO_DEBUG) fprintf(stderr, "[%s] entry (context = %p, stack = %p ... %p)\n", __func__, context, stack, (char *)stack + size);
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 *)stack + size;
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(¤t->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 */
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