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Implemented lazy stack symbolization.
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Previously, when an exception was thrown, the exception got 'stack'
property attached which contained the backtrace information about where
the exception happened. This could be a heavy operation and it was not
always needed.

To optimize it, the process is split into 2 phases. The first phase
collects all the necessary info about the current stack. The second
phase, where the stack symbolization happens, occurs only when this
property is referenced.
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@xeioex
xeioex committed Oct 17, 2024
1 parent 6ed6c10 commit eda6fa7
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Showing 3 changed files with 150 additions and 45 deletions.
182 changes: 138 additions & 44 deletions src/njs_error.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,15 @@
#include <njs_main.h>


typedef struct {
union {
njs_function_t *function;
u_char *pc;
} u;
uint8_t native;
} njs_stack_entry_t;


typedef struct {
njs_str_t name;
njs_str_t file;
Expand All @@ -16,7 +25,7 @@ typedef struct {


static njs_int_t njs_add_backtrace_entry(njs_vm_t *vm, njs_arr_t *stack,
njs_native_frame_t *native_frame);
njs_stack_entry_t *se);
static njs_int_t njs_backtrace_to_string(njs_vm_t *vm, njs_arr_t *backtrace,
njs_str_t *dst);

Expand Down Expand Up @@ -87,33 +96,34 @@ njs_error_fmt_new(njs_vm_t *vm, njs_value_t *dst, njs_object_type_t type,


static njs_int_t
njs_error_stack_new(njs_vm_t *vm, njs_object_t *error, njs_value_t *retval)
njs_error_stack_new(njs_vm_t *vm, njs_object_value_t *error)
{
njs_int_t ret;
njs_str_t string;
njs_arr_t *stack;
njs_value_t value;
njs_stack_entry_t *se;
njs_native_frame_t *frame;

njs_set_object(&value, error);

ret = njs_error_to_string(vm, retval, &value);
if (njs_slow_path(ret != NJS_OK)) {
return ret;
}

stack = njs_arr_create(vm->mem_pool, 4, sizeof(njs_backtrace_entry_t));
stack = njs_arr_create(vm->mem_pool, 4, sizeof(njs_stack_entry_t));
if (njs_slow_path(stack == NULL)) {
return NJS_ERROR;
}

frame = vm->top_frame;

for ( ;; ) {
if ((frame->native || frame->pc != NULL)
&& njs_add_backtrace_entry(vm, stack, frame) != NJS_OK)
{
break;
if (frame->native || frame->pc != NULL) {
se = njs_arr_add(stack);
if (njs_slow_path(se == NULL)) {
return NJS_ERROR;
}

se->native = frame->native;

if (se->native) {
se->u.function = frame->function;

} else {
se->u.pc = frame->pc;
}
}

frame = frame->previous;
Expand All @@ -123,25 +133,16 @@ njs_error_stack_new(njs_vm_t *vm, njs_object_t *error, njs_value_t *retval)
}
}

njs_string_get(retval, &string);

ret = njs_backtrace_to_string(vm, stack, &string);

njs_arr_destroy(stack);

if (njs_slow_path(ret != NJS_OK)) {
return ret;
}
njs_data(&error->value) = stack;

return njs_string_create(vm, retval, string.start, string.length);
return NJS_OK;
}


njs_int_t
njs_error_stack_attach(njs_vm_t *vm, njs_value_t value)
{
njs_int_t ret;
njs_value_t stack;
njs_int_t ret;

if (njs_slow_path(!njs_is_error(&value))
|| njs_object(&value)->stack_attached)
Expand All @@ -153,18 +154,15 @@ njs_error_stack_attach(njs_vm_t *vm, njs_value_t value)
return NJS_OK;
}

ret = njs_error_stack_new(vm, njs_object(&value), &stack);
ret = njs_error_stack_new(vm, value.data.u.object_value);
if (njs_slow_path(ret != NJS_OK)) {
njs_internal_error(vm, "njs_error_stack_new() failed");
return NJS_ERROR;
}

njs_object(&value)->stack_attached = 1;

return njs_object_prop_define(vm, &value,
njs_value_arg(&njs_error_stack_string),
&stack, NJS_OBJECT_PROP_VALUE_CW,
NJS_STACK_HASH);
return NJS_OK;
}


Expand Down Expand Up @@ -194,16 +192,20 @@ njs_error_alloc(njs_vm_t *vm, njs_object_t *proto, const njs_value_t *name,
njs_int_t ret;
njs_object_t *error;
njs_object_prop_t *prop;
njs_object_value_t *ov;
njs_lvlhsh_query_t lhq;

error = njs_mp_alloc(vm->mem_pool, sizeof(njs_object_t));
if (njs_slow_path(error == NULL)) {
ov = njs_mp_alloc(vm->mem_pool, sizeof(njs_object_value_t));
if (njs_slow_path(ov == NULL)) {
goto memory_error;
}

njs_set_data(&ov->value, NULL, NJS_DATA_TAG_ANY);

error = &ov->object;
njs_lvlhsh_init(&error->hash);
njs_lvlhsh_init(&error->shared_hash);
error->type = NJS_OBJECT;
error->type = NJS_OBJECT_VALUE;
error->shared = 0;
error->extensible = 1;
error->fast_array = 0;
Expand Down Expand Up @@ -485,15 +487,18 @@ const njs_object_init_t njs_aggregate_error_constructor_init = {
void
njs_memory_error_set(njs_vm_t *vm, njs_value_t *value)
{
njs_object_t *object;
njs_object_t *object;
njs_object_value_t *ov;

object = &vm->memory_error_object;
ov = &vm->memory_error_object;
njs_set_data(&ov->value, NULL, NJS_DATA_TAG_ANY);

object = &ov->object;
njs_lvlhsh_init(&object->hash);
njs_lvlhsh_init(&object->shared_hash);
object->__proto__ = njs_vm_proto(vm, NJS_OBJ_TYPE_INTERNAL_ERROR);
object->slots = NULL;
object->type = NJS_OBJECT;
object->type = NJS_OBJECT_VALUE;
object->shared = 1;

/*
Expand Down Expand Up @@ -691,6 +696,92 @@ njs_error_prototype_to_string(njs_vm_t *vm, njs_value_t *args, njs_uint_t nargs,
}


static njs_int_t
njs_error_prototype_stack(njs_vm_t *vm, njs_object_prop_t *prop,
njs_value_t *value, njs_value_t *setval, njs_value_t *retval)
{
njs_int_t ret;
njs_str_t string;
njs_arr_t *stack, *backtrace;
njs_uint_t i;
njs_value_t rv, *stackval;
njs_stack_entry_t *se;

if (retval != NULL) {
if (!njs_is_error(value)) {
njs_set_undefined(retval);
return NJS_DECLINED;
}

stackval = njs_object_value(value);

if (setval != NULL) {
njs_value_assign(stackval, setval);
return NJS_OK;
}

if (!njs_is_data(stackval, NJS_DATA_TAG_ANY)) {
njs_value_assign(retval, stackval);
return NJS_OK;
}

stack = njs_data(stackval);
if (stack == NULL) {
njs_set_undefined(retval);
return NJS_OK;
}

se = stack->start;

backtrace = njs_arr_create(vm->mem_pool, stack->items,
sizeof(njs_backtrace_entry_t));
if (njs_slow_path(backtrace == NULL)) {
return NJS_ERROR;
}

for (i = 0; i < stack->items; i++) {
if (njs_add_backtrace_entry(vm, backtrace, &se[i]) != NJS_OK) {
return NJS_ERROR;
}
}

ret = njs_error_to_string2(vm, &rv, value, 0);
if (njs_slow_path(ret != NJS_OK)) {
return ret;
}

njs_string_get(&rv, &string);

ret = njs_backtrace_to_string(vm, backtrace, &string);

njs_arr_destroy(backtrace);
njs_arr_destroy(stack);

if (njs_slow_path(ret != NJS_OK)) {
return ret;
}

ret = njs_string_create(vm, stackval, string.start, string.length);
if (njs_slow_path(ret != NJS_OK)) {
return ret;
}

njs_value_assign(retval, stackval);

return NJS_OK;
}

/* Delete. */

if (njs_is_error(value)) {
stackval = njs_object_value(value);
njs_set_data(stackval, NULL, NJS_DATA_TAG_ANY);
}

return NJS_OK;
}


njs_int_t
njs_error_to_string(njs_vm_t *vm, njs_value_t *retval, const njs_value_t *error)
{
Expand All @@ -717,6 +808,9 @@ static const njs_object_prop_t njs_error_prototype_properties[] =
NJS_DECLARE_PROP_NATIVE("valueOf", njs_error_prototype_value_of, 0, 0),

NJS_DECLARE_PROP_NATIVE("toString", njs_error_prototype_to_string, 0, 0),

NJS_DECLARE_PROP_HANDLER("stack", njs_error_prototype_stack,
0, 0, NJS_OBJECT_PROP_VALUE_CW),
};


Expand Down Expand Up @@ -986,14 +1080,14 @@ const njs_object_type_init_t njs_aggregate_error_type_init = {

static njs_int_t
njs_add_backtrace_entry(njs_vm_t *vm, njs_arr_t *stack,
njs_native_frame_t *native_frame)
njs_stack_entry_t *se)
{
njs_int_t ret;
njs_vm_code_t *code;
njs_function_t *function;
njs_backtrace_entry_t *be;

function = native_frame->function;
function = se->native ? se->u.function : NULL;

if (function != NULL && function->bound != NULL) {
/* Skip. */
Expand All @@ -1019,7 +1113,7 @@ njs_add_backtrace_entry(njs_vm_t *vm, njs_arr_t *stack,
return NJS_OK;
}

code = njs_lookup_code(vm, native_frame->pc);
code = njs_lookup_code(vm, se->u.pc);

if (code != NULL) {
be->name = code->name;
Expand All @@ -1028,7 +1122,7 @@ njs_add_backtrace_entry(njs_vm_t *vm, njs_arr_t *stack,
be->name = njs_entry_anonymous;
}

be->line = njs_lookup_line(code->lines, native_frame->pc - code->start);
be->line = njs_lookup_line(code->lines, se->u.pc - code->start);
if (!vm->options.quiet) {
be->file = code->file;
}
Expand Down
2 changes: 1 addition & 1 deletion src/njs_vm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,7 @@ struct njs_vm_s {
* MemoryError is statically allocated immutable Error object
* with the InternalError prototype.
*/
njs_object_t memory_error_object;
njs_object_value_t memory_error_object;

njs_object_t string_object;
njs_object_t global_object;
Expand Down
11 changes: 11 additions & 0 deletions src/test/njs_benchmark.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -116,6 +116,7 @@ njs_benchmark_test(njs_vm_t *parent, njs_opts_t *opts, njs_value_t *report,

njs_vm_opt_init(&options);

options.backtrace = 1;
options.addons = njs_benchmark_addon_external_modules;

vm = NULL;
Expand Down Expand Up @@ -468,6 +469,16 @@ static njs_benchmark_test_t njs_test[] =
njs_str("$shared.method('YES')"),
njs_str("shared"),
1000 },

{ "exception",
njs_str("function f() { try { throw new Error('test') } catch (e) { return e.message } } [f].map(v=>v())[0]"),
njs_str("test"),
10000 },

{ "exception.stack",
njs_str("function f() { try { throw new Error('test') } catch (e) { return e.stack } } [f].map(v=>v())[0]"),
njs_str("Error: test\n at f (:1)\n at anonymous (:1)\n at Array.prototype.map (native)\n at main (:1)\n"),
100 },
};


Expand Down

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