plotly.show() does not work on Windows 10

[ana-jiangR]

By design, the API "plot.show()" would open a default web browser to display an interactive plot.
However, under my environment(Windows 10, plotly="0.8.3"), it doesn't work. The default web browser was not opened either.

I found out that there was an issue message from cmd:
The process cannot access the file because it is being used by another process

https://github.com/igiagkiozis/plotly/blob/49bd3a87fbaa3e507e9a2664f57feda89c35b95b/plotly/src/plot.rs#L465

//Line 465
    #[cfg(target_os = "windows")]
    fn show_with_default_app(temp_path: &str) {
        use std::process::Command;
        Command::new("cmd")
            .arg("/C")
            .arg(format!(r#"start {}"#, temp_path))
            .output()
            .expect(DEFAULT_HTML_APP_NOT_FOUND);
    }

After investigation, I suspect it's because, that the temp html file that should be opened was being used by another process, while this "another" process is the process itself which has not yet close the file handle in Rust program.

Could you fix this please? Thanks! :)

[mfreeborn]

I would gratefully accept a PR with a fix - I'm short on time at the moment to fix this personally. I'm not immediately sure why it works on linux but not Windows; the implementations should be equivalent.

[juanespj]

Hello I was playing with this function and figured it out I will send a pull request with this!!

    fn show_with_default_app(temp_path: &str) {
        use std::process::Command;
        Command::new("cmd")
            .arg(format!("/Cstart {}", temp_path))
            .spawn()
                .expect(DEFAULT_HTML_APP_NOT_FOUND);
            // .output()
            // .expect(DEFAULT_HTML_APP_NOT_FOUND);
    }```

[mfreeborn]

Closed by #129

[GSTRonnie]

I also came upon this problem and figured out that it can be resolved by closing the file in Plot::show(), for example enclosing it in a scope, before calling Plot::show_with_default_app(). E.g.:

// Save the rendered plot to the temp file.
let temp_path = temp.to_str().unwrap();
{
    let mut file = File::create(temp_path).unwrap();
    file.write_all(rendered.as_bytes())
        .expect("failed to write html output");
    file.flush().unwrap();
}

// Hand off the job of opening the browser to an OS-specific implementation.
Plot::show_with_default_app(temp_path);

[mfreeborn]

Hmm, I wonder if this is a more robust solution than #129. It's always good to release resources as early as possible for exactly this reason.