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// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

pub mod actor;
pub mod environment;

mod actor_runner;
mod counter;

use crate::counter::start_counter;
use crate::environment::Environment;
use fuchsia_async::{MonotonicInstant, Timer};
use futures::future::{select, Aborted, Either};
use futures::stream::FuturesUnordered;
use futures::StreamExt;
use rand::rngs::SmallRng;
use rand::{Rng, SeedableRng};
use std::pin::pin;
use std::time::Duration;
use tracing::{error, info};

/// Use entropy to generate a random seed
pub fn random_seed() -> u64 {
    let mut temp_rng = SmallRng::from_entropy();
    temp_rng.gen()
}

/// Runs the test loop for the given environment to completion.
pub async fn run_test<E: 'static + Environment>(mut env: E) {
    let env_string = format!("{:#?}", env);

    info!("--------------------- stressor is starting -----------------------");
    info!("{}", env_string);
    info!("------------------------------------------------------------------");

    {
        // Setup a panic handler that prints out details of this invocation on crash
        let default_panic_hook = std::panic::take_hook();
        let custom_panic_hook = env.panic_hook();
        std::panic::set_hook(Box::new(move |panic_info| {
            error!("");
            error!("--------------------- stressor has crashed -----------------------");
            error!("{}", env_string);
            error!("------------------------------------------------------------------");
            error!("");
            if let Some(hook) = &custom_panic_hook {
                hook();
            }
            default_panic_hook(panic_info);
        }));
    }

    // Extract the data from the environment
    // Defaults:
    // - target_operations: 2^64
    // - timeout_secs: 24 hours
    let target_operations = env.target_operations().unwrap_or(u64::MAX);
    let timeout_secs = Duration::from_secs(env.timeout_seconds().unwrap_or(24 * 60 * 60));

    // Start the counter thread
    // The counter thread keeps track of the global operation count.
    // Each actor will send a message to the counter thread when an operation is completed.
    // When the target operation count is hit, the counter task exits.
    let (counter_task, counter_tx) = start_counter(target_operations);

    // Create a timeout task
    let timeout = pin!(Timer::new(MonotonicInstant::after(timeout_secs.into())));
    let mut test_end = pin!(select(counter_task, timeout));

    // A monotonically increasing counter representing the current generation.
    // On every environment reset, the generation is incremented.
    let mut generation: u64 = 0;

    // Start all the runners
    let (mut runner_tasks, mut runner_abort): (FuturesUnordered<_>, Vec<_>) = env
        .actor_runners()
        .await
        .into_iter()
        .map(|r| r.run(counter_tx.clone(), generation))
        .unzip();

    loop {
        // Wait for one of the runners, counter task or timer to return
        let either = select(test_end, runner_tasks.next()).await;
        match either {
            Either::Left((test_end_either, _next)) => {
                let reason = match test_end_either {
                    Either::Left(..) => "operation count",
                    Either::Right(..) => "timeout",
                };

                // The counter/timer task returned.
                // The target operation count was hit or the timer expired.
                // The test has completed.
                info!(%reason, "Stress test has completed!");
                for abort in runner_abort {
                    abort.abort();
                }
                // We don't care if tasks finished or were aborted, but we want them not running
                // anymore before we return.
                //
                // Runaway threads can cause problems if they're using objects from the main
                // executor, and it's generally a good idea to clean up after ourselves here.
                let () = runner_tasks.map(|_: Result<_, Aborted>| ()).collect().await;
                break;
            }
            Either::Right((None, _counter_task)) => {
                info!("No runners to operate");
                break;
            }
            Either::Right((Some(result), task)) => {
                let (runner, runner_generation) = result.expect("no tasks have been aborted");
                // Normally, actor runners run indefinitely.
                // However, one of the actor runners has returned.
                // This is because an actor has requested an environment reset.

                // Move the counter/timer back
                test_end = task;

                // Did the runner request a reset at the current generation?
                if runner_generation == generation {
                    // Reset the environment
                    info!("Resetting environment");
                    env.reset().await;

                    // Advance the generation
                    generation += 1;
                }

                // Restart this runner with the current generation
                let (task, abort) = runner.run(counter_tx.clone(), generation);
                runner_tasks.push(task);
                runner_abort.push(abort);
            }
        }
    }
}