slowjs: A C repository from wuchuheng

SlowJS

SlowJS - QuickJS is quick but I can make it slow!

Learning the awesome QuickJS by extending it with below functionalities:

Divide the 5.4W LoC quickjs.c into multiple small files, makes the code easy to browser and navigate
A debugger which supports inline breakpoints and includes web interfaces which is easy to integrate with the Debug Adapter Protocol
Dump the GC managed objects and view the results in the Chrome devtools

Debugger

The debugger can be tasted by following steps:

Click to expand

Build our SlowJS:
```
cmake -S . --preset=default
cmake --build --preset=qjs
```
the location of the built stuff is ./build/qjs/qjs

Make up a file tmp_test.js to test:

function add(a, b) {
  const c = a + b;
  return c;
}

function sub(a, b) {
  const c = a - b;
  return c;
}

function doSth(a, b) {
  return add(a, b) + sub(a, b);
}

print(doSth(1, 2));

Start the debugger:
```
./build/qjs/qjs --debug 8097
```
Connect to the debugger:
```
nc 0.0.0.0 8097
```
We use nc to communicate with the debugger server, then we can paste come commands to perform debug
Call the debugger to launch a new session:
```
{ "type": "launch", "data": { "file": "./tmp_test.js" } }
```
Paste above json into the nc REPL and press ENTER

Set breakpoints:

{
  "type": "setBreakpoint",
  "data": { "file": "./tmp_test.js", "line": 3, "col": 0 }
}

{
  "type": "setBreakpoint",
  "data": { "file": "./tmp_test.js", "line": 8, "col": 0 }
}

Start to run our test script:
```
{ "type": "run" }
```

Now the debugger is paused at the first breakpoint, we can list the stack frames:

{ "type": "listStackframes" }

the output looks like:

{
  "type": "listStackframes",
  "data": [
    {
      "name": "add",
      "file": "./tmp_test.js",
      "line": 1
    },
    {
      "name": "doSth",
      "file": "./tmp_test.js",
      "line": 11
    },
    {
      "name": "<eval>",
      "file": "./tmp_test.js",
      "line": 1
    }
  ]
}

We can resume the debugger by issuing below command:
```
{ "type": "continue" }
```

Now the debugger is paused at the second breakpoint, we can print the variable in the topmost stack frame:

{ "type": "dumpStackframe", "data": { "i": 0 } }

the output looks like:

{
  "type": "dumpStackframe",
  "data": {
    "args": [
      {
        "name": "a",
        "value": 1
      },
      {
        "name": "b",
        "value": 2
      }
    ],
    "vars": [
      {
        "name": "c",
        "value": -1
      }
    ],
    "closure_vars": [],
    "name": "sub",
    "file": "./tmp_test.js",
    "line": 6
  }
}

We can use the continue command resume the debugger again:
```
{ "type": "continue" }
```
Now the test script is done and the debugger server prints the final results:
```
new sess thread is running...
2
```

GC Dump

The GC dump functionality can be tasted by following steps:

Click to expand

Build our SlowJS:
```
cmake -S . --preset=default
cmake --build --preset=qjs
```
the location of the built stuff is ./build/qjs/qjs

Make up a file tmp_test.js to test:

var o = {
  a: { a1: { a2: 1 } },
  b: { b1: { b2: 1 } },
  c: function () {
    return 1;
  },
  d: new ArrayBuffer((1 << 20) * 50, 0),
  e: new Uint16Array((1 << 20) * 50, 0),
};

__js_gcdump_objects();
print(o); // retain the obj to prevent it from being freed

Run the test script:
```
./build/qjs/qjs tmp_test.js
```
The output file will have name looks like:
```
Heap.20230318.130209.224.heapsnapshot
```
the filename is in this pattern:
```
Heap.date.time.ms.heapsnapshot
```
Import the output file into Chrome devtools:
Then we can dig into the heap:

Development

It's better to glance over the available options before you perform the actual build:

cmake -B build -LH

-B stands for the building directory

-L stands for listing all the options

-H stands for printing the help messages along with the options

above command will print the available options and their help messages, use them like this:

cmake -B build -S . -G Ninja -D QJS_DUMP_BYTECODE=1

-S stands for the source directory

-D stands for specifying an options in a key=value pattern

then choose one of below sections to run in project root directory

Debug build

cmake -S . --preset=default
cmake --build --preset=qjs

Release build

cmake -S . --preset=default -D CMAKE_BUILD_TYPE=Release
cmake --build --preset=qjs

Tests

cmake -S . --preset=default
cmake --build --preset=run-tests

Microbench

cmake -S . --preset=default -D CMAKE_BUILD_TYPE=Release
cmake --build --preset=run-microbench

Test262

cmake -S . --preset=default -D CMAKE_BUILD_TYPE=Release
cmake --build --preset=run-test262

# Result: 302/75790 errors, 1396 excluded, 7712 skipped, 302 new

Presets

You can also choose the presets listed in CMakePresets.json to run:

# Use a config preset
cmake -S . --preset=default

# Use a build preset
cmake --build --preset=run-tests

wuchuheng/slowjs