agiledancers/ci/runner/WaitForDocker.java

import java.time.Duration;
import java.util.concurrent.TimeUnit;

/** Source-launcher startup probe; uses the service's configured DOCKER_HOST. */
class WaitForDocker {
    public static void main(String[] args) throws Exception {
        long seconds = args.length == 0 ? 120 : Long.parseLong(args[0]);
        if (seconds < 1 || seconds > 300) throw new IllegalArgumentException("Timeout must be 1–300 seconds");
        long deadline = System.nanoTime() + Duration.ofSeconds(seconds).toNanos();
        System.out.println("Waiting for the configured Docker engine...");
        while (System.nanoTime() < deadline) {
            Process process = new ProcessBuilder("docker", "info", "--format", "{{.ServerVersion}}")
                    .redirectOutput(ProcessBuilder.Redirect.DISCARD)
                    .redirectError(ProcessBuilder.Redirect.DISCARD)
                    .start();
            try {
                long remaining = Math.max(1, deadline - System.nanoTime());
                if (process.waitFor(Math.min(remaining, TimeUnit.SECONDS.toNanos(5)), TimeUnit.NANOSECONDS)
                        && process.exitValue() == 0) {
                    System.out.println("Docker is available; starting the Gitea runner.");
                    return;
                }
            } finally {
                if (process.isAlive()) {
                    process.destroyForcibly();
                    process.waitFor();
                }
            }
            long remaining = deadline - System.nanoTime();
            if (remaining > 0) TimeUnit.NANOSECONDS.sleep(Math.min(remaining, TimeUnit.SECONDS.toNanos(2)));
        }
        System.err.println("Docker did not become available within " + seconds + " seconds; runner not started.");
        System.exit(1);
    }
}