Show current thread id and process id

[vini-fda]

Currently, PID and TID are hardcoded to show only the constant "1":

fn write_results_recursive(file: &mut File, result: &GpuTimerScopeResult, last: bool) -> std::io::Result<()> {
    write!(
        file,
        r#"{{ "pid":1, "tid":1, "ts":{}, "dur":{}, "ph":"X", "name":"{}" }}{}"#,
        result.time.start * 1000.0 * 1000.0,
        (result.time.end - result.time.start) * 1000.0 * 1000.0,
        result.label,
        if last && result.nested_scopes.is_empty() { "\n" } else { ",\n" }
    )?;
    if result.nested_scopes.is_empty() {
        return Ok(());
    }

    for child in result.nested_scopes.iter().take(result.nested_scopes.len() - 1) {
        write_results_recursive(file, child, false)?;
    }
    write_results_recursive(file, result.nested_scopes.last().unwrap(), last)?;

    Ok(())
    // { "pid":1, "tid":1, "ts":546867, "dur":121564, "ph":"X", "name":"DoThings"
}

They should be changed to output the proper process and thread id.

Suggestion: use std::process::id() for the PID and std::thread::current().id() for the TID. The only problem is that the ThreadId type in the standard library cannot be trivially converted to a primitive type (int/uint/usize), without using any hacks. Also, ThreadIds are under the control of Rust’s standard library and there may not be any relationship between ThreadId and the underlying platform’s notion of a thread identifier (see the official docs). There's a proposal for stabilizing a u64 conversion, though (see this tracking issue)