84 lines
2.8 KiB
C
84 lines
2.8 KiB
C
/*
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This is a ucontext-like userland context switching API for WebAssembly based on Binaryen's Asyncify.
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* NOTE:
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* This mechanism doesn't take care of stack state. Just save and restore program counter and
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* registers (rephrased as locals by Wasm term). So use-site need to save and restore the C stack pointer.
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* This Asyncify based implementation is not much efficient and will be replaced with future stack-switching feature.
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*/
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#include <stdlib.h>
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#include "wasm/fiber.h"
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#include "wasm/asyncify.h"
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#ifdef RB_WASM_ENABLE_DEBUG_LOG
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# include <stdio.h>
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# define RB_WASM_DEBUG_LOG(...) fprintf(stderr, __VA_ARGS__)
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#else
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# define RB_WASM_DEBUG_LOG(...)
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#endif
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void
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rb_wasm_init_context(rb_wasm_fiber_context *fcp, void (*func)(void *, void *), void *arg0, void *arg1)
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{
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fcp->asyncify_buf.top = &fcp->asyncify_buf.buffer[0];
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fcp->asyncify_buf.end = &fcp->asyncify_buf.buffer[WASM_FIBER_STACK_BUFFER_SIZE];
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fcp->is_rewinding = false;
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fcp->is_started = false;
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fcp->entry_point = func;
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fcp->arg0 = arg0;
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fcp->arg1 = arg1;
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RB_WASM_DEBUG_LOG("[%s] fcp->asyncify_buf %p\n", __func__, &fcp->asyncify_buf);
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}
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static rb_wasm_fiber_context *_rb_wasm_active_next_fiber;
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void
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rb_wasm_swapcontext(rb_wasm_fiber_context *ofcp, rb_wasm_fiber_context *fcp)
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{
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RB_WASM_DEBUG_LOG("[%s] enter ofcp = %p fcp = %p\n", __func__, ofcp, fcp);
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if (ofcp->is_rewinding) {
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asyncify_stop_rewind();
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ofcp->is_rewinding = false;
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return;
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}
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_rb_wasm_active_next_fiber = fcp;
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RB_WASM_DEBUG_LOG("[%s] start unwinding asyncify_buf = %p\n", __func__, &ofcp->asyncify_buf);
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asyncify_start_unwind(&ofcp->asyncify_buf);
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}
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void *
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rb_wasm_handle_fiber_unwind(void (**new_fiber_entry)(void *, void *),
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void **arg0, void **arg1, bool *is_new_fiber_started)
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{
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rb_wasm_fiber_context *next_fiber;
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if (!_rb_wasm_active_next_fiber) {
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RB_WASM_DEBUG_LOG("[%s] no next fiber\n", __func__);
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*is_new_fiber_started = false;
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return NULL;
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}
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next_fiber = _rb_wasm_active_next_fiber;
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_rb_wasm_active_next_fiber = NULL;
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RB_WASM_DEBUG_LOG("[%s] next_fiber->asyncify_buf = %p\n", __func__, &next_fiber->asyncify_buf);
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*new_fiber_entry = next_fiber->entry_point;
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*arg0 = next_fiber->arg0;
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*arg1 = next_fiber->arg1;
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if (!next_fiber->is_started) {
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RB_WASM_DEBUG_LOG("[%s] new fiber started\n", __func__);
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// start a new fiber if not started yet.
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next_fiber->is_started = true;
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*is_new_fiber_started = true;
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return NULL;
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} else {
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RB_WASM_DEBUG_LOG("[%s] resume a fiber\n", __func__);
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// resume a fiber again
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next_fiber->is_rewinding = true;
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*is_new_fiber_started = false;
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return &next_fiber->asyncify_buf;
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}
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}
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