Executing std.process synchronously from vibe.d sometimes silently hangs the server

Question

I wrote a vibe.d web-UI for clang-format, when presented with this input while using LLVM style, the server hangs.

The code for handling POST:

void post(string style, string code)
{
    import std.algorithm;
    import std.file;
    import std.conv;
    import std.process;
    auto pipes = pipeProcess(["clang-format", "-style="~style], Redirect.stdout | Redirect.stdin);
    scope(exit) wait(pipes.pid);

    pipes.stdin.write(code);
    pipes.stdin.close;
    pipes.pid.wait;

    code = pipes.stdout.byLine.joiner.to!string;

    string selectedStyle = style;

    render!("index.dt", styles, code, selectedStyle);
}

This probably shouldn't be done in a blocking way, but I am at a loss how to do it asynchronously. I have tried wrapping the contents of the function in runTask, but I couldn't figure out a way to call it correctly.

How can I make it reliable?

Answer 1

You are probably writing too much data to the program's stdin without reading its stdout. Since the pipe buffer size is limited, this causes the executed program to block on writing to its stdout, which in turn causes your program to block on writing to its stdin.

The solution is to read data as you are writing it. A simple way to do it is to create a second thread which reads the data, while the main thread writes it.