add JS_WriteMemeroyUsage for reporting back memory usage out in different ways

[Vizonex]

I recently saw this project as a good candidate for a new Javascript interpreter library for Python & Cython and as I was going about binding python and quickjs-ng together I came across an issue with using FILE* pointers since Python does not have a very clear way of gaining access to these FILE* pointers and I saw extracting objects from PyObject* to const char* types to be rather annoying and not very efficient and may limit what programmers may be able to do with this data so I decided to write a newer callback system to try and make up for this. annoyance. The way I plan to use it in Cython will be the following code.

But for the code I'm demonstrating I'll cut to the important stuff that makes use of these functions that I am needing.

cdef int js_write_memory_usage_cb(void* opaque, const char* data, size_t data_len) noexcept with gil:
    cdef str py_data
    cdef object write_cb = <object>opaque
    try:
        PyObject_CallOneArg(write_cb, PyUnicode_FromStringAndSize(data, data_len))
        # success!
        return 0
    except BaseException:
        # reraise later...
        return -1
 

cdef class Runtime:
    """
    Represents a JavaScript runtime corresponding to an
    object heap. Several runtimes can exist at the same time but they
    cannot exchange objects. Inside a given runtime, no multi-threading is
    supported.
    """
    cdef:
        JSRuntime* rt
    
    cpdef object dump_memory_usage(self, object io):
        """dumps memory to an StringIO type object or file type object"""
        cdef object write = io.write # SEE: https://docs.python.org/3/c-api/file.html
        cdef JSMemoryUsage memory_usage
        cdef int ret
        JS_ComputeMemoryUsage(self.rt, &memory_usage)
        
        ret = JS_WriteMemoryUsage(js_write_memory_usage_cb, memory_usage, self.rt, <void*>(write))
        if ret < 0:
            # Reraise Last Seen Python Exception
            raise

Please let me know if any names or things in these additions should be changed or if there's a better way for me to come up with a less costly implementation for the library I am planning to make.

[bnoordhuis]

I can understand the issue with JS_DumpMemoryUsage() but can you explain why JS_ComputeMemoryUsage() is not sufficient for your use case?

Apropos FILE pointers, you can create one from a memory buffer with fmemopen().

[Vizonex]

@bnoordhuis Problem solved. Cython has a few unexposed functions that is doesn't utilize that I can use by having them shoved into a headerfile.

static PyObject* CYJS_FSConvert(PyObject* file){
    PyObject* filename_bytes = NULL;
    if (PyUnicode_FSConverter(file, &filename_bytes) < 0)
        return NULL;
    return filename_bytes;
}

static int CYJS_DumpMemoryUsage(JSRuntime* rt, PyObject* file){
    
    PyObject* filename_bytes = NULL;
    JSMemoryUsage mu;

    // Me being aggressive
    if (rt == NULL || file == NULL){
        PyErr_SetString(PyExc_TypeError, "(runtime & file) cannot be passed as NULL");
        return -1;
    }

    // Kinda stupid how cython doesn't make use of this function 
    // when it serves great importance with python's built-in open() function
    if (PyUnicode_FSConverter(file, &filename_bytes) < 0)
        return -1;

    // We need a file pointer.
    FILE* fp = fopen((const char*)PyBytes_AS_STRING(filename_bytes), "w");
    if (fp == NULL){
        PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, file);
        Py_CLEAR(filename_bytes);
        return -1;
    }
    JS_ComputeMemoryUsage(rt, &mu);
    JS_DumpMemoryUsage(fp, (const JSMemoryUsage*)(&mu), rt);
    fclose(fp);
    Py_CLEAR(filename_bytes);
    return 0;
}

You will find this code in my new library CYJS