fix(test) switch zebrad to a non-blocking tracing logger

zebra-state/src/service/finalized_state.rs

@@ -106,6 +106,11 @@ impl FinalizedState {
                 // So we want to drop it before we exit.
                 std::mem::drop(new_state);
 
+                // Drops tracing log output that's hasn't already been written to stdout
+                // since this exits before calling drop on the WorkerGuard for the logger thread.
+                // This is okay for now because this is test-only code
+                //
+                // TODO: Call ZebradApp.shutdown or drop its Tracing component before calling exit_process to flush logs to stdout
                 Self::exit_process();
             }
         }
@@ -307,6 +312,11 @@ impl FinalizedState {
             // We're just about to do a forced exit, so it's ok to do a forced db shutdown
             self.db.shutdown(true);
 
+            // Drops tracing log output that's hasn't already been written to stdout
+            // since this exits before calling drop on the WorkerGuard for the logger thread.
+            // This is okay for now because this is test-only code
+            //
+            // TODO: Call ZebradApp.shutdown or drop its Tracing component before calling exit_process to flush logs to stdout
             Self::exit_process();
         }
 
@@ -343,6 +353,9 @@ impl FinalizedState {
         let _ = stdout().lock().flush();
         let _ = stderr().lock().flush();
 
+        // Exits before calling drop on the WorkerGuard for the logger thread,
+        // dropping any lines that haven't already been written to stdout.
+        // This is okay for now because this is test-only code
         std::process::exit(0);
     }
 }

zebrad/Cargo.toml

@@ -99,6 +99,7 @@ tinyvec = { version = "1.6.0", features = ["rustc_1_55"] }
 thiserror = "1.0.33"
 
 tracing-subscriber = { version = "0.3.11", features = ["env-filter"] }
+tracing-appender = "0.2.2"
 tracing-error = "0.2.0"
 tracing-futures = "0.2.5"
 tracing = "0.1.31"

zebrad/src/application.rs

@@ -6,7 +6,7 @@ use self::entry_point::EntryPoint;
 use std::{fmt::Write as _, io::Write as _, process};
 
 use abscissa_core::{
-    application::{self, fatal_error, AppCell},
+    application::{self, AppCell},
     config::{self, Configurable},
     status_err,
     terminal::{component::Terminal, stderr, stdout, ColorChoice},
@@ -18,6 +18,13 @@ use zebra_state::constants::{DATABASE_FORMAT_VERSION, LOCK_FILE_ERROR};
 
 use crate::{commands::ZebradCmd, components::tracing::Tracing, config::ZebradConfig};
 
+/// See <https://docs.rs/abscissa_core/latest/src/abscissa_core/application/exit.rs.html#7-10>
+/// Print a fatal error message and exit
+fn fatal_error(app_name: String, err: &dyn std::error::Error) -> ! {
+    status_err!("{} fatal error: {}", app_name, err);
+    process::exit(1)
+}
+
 /// Application state
 pub static APPLICATION: AppCell<ZebradApp> = AppCell::new();
 
@@ -462,7 +469,11 @@ impl Application for ZebradApp {
         let _ = stderr().lock().flush();
 
         if let Err(e) = self.state().components.shutdown(self, shutdown) {
-            fatal_error(self, &e)
+            let app_name = self.name().to_string();
+
+            // Swap out a fake app so we can trigger the destructor on the original
+            let _ = std::mem::take(self);
+            fatal_error(app_name, &e);
         }
 
         // Swap out a fake app so we can trigger the destructor on the original

zebrad/src/components/tracing/component.rs

@@ -3,9 +3,15 @@
 use abscissa_core::{Component, FrameworkError, Shutdown};
 use tracing_error::ErrorLayer;
 use tracing_subscriber::{
-    fmt::Formatter, layer::SubscriberExt, reload::Handle, util::SubscriberInitExt, EnvFilter,
+    fmt::{format, Formatter},
+    layer::SubscriberExt,
+    reload::Handle,
+    util::SubscriberInitExt,
+    EnvFilter,
 };
 
+use tracing_appender::non_blocking::{NonBlocking, NonBlockingBuilder, WorkerGuard};
+
 use crate::{application::app_version, config::TracingSection};
 
 #[cfg(feature = "flamegraph")]
@@ -16,14 +22,23 @@ pub struct Tracing {
     /// The installed filter reloading handle, if enabled.
     //
     // TODO: when fmt::Subscriber supports per-layer filtering, remove the Option
-    filter_handle: Option<Handle<EnvFilter, Formatter>>,
+    filter_handle: Option<
+        Handle<
+            EnvFilter,
+            Formatter<format::DefaultFields, format::Format<format::Full>, NonBlocking>,
+        >,
+    >,
 
     /// The originally configured filter.
     initial_filter: String,
 
     /// The installed flame graph collector, if enabled.
     #[cfg(feature = "flamegraph")]
     flamegrapher: Option<flame::Grapher>,
+
+    /// Drop guard for worker thread of non-blocking logger,
+    /// responsible for flushing any remaining logs when the program terminates
+    _guard: WorkerGuard,
 }
 
 impl Tracing {
@@ -32,6 +47,13 @@ impl Tracing {
         let filter = config.filter.unwrap_or_else(|| "".to_string());
         let flame_root = &config.flamegraph;
 
+        // Builds a lossy NonBlocking logger with a default line limit of 128_000 or an explicit buffer_limit.
+        // The write method queues lines down a bounded channel with this capacity to a worker thread that writes to stdout.
+        // Increments error_counter and drops lines when the buffer is full.
+        let (non_blocking, _guard) = NonBlockingBuilder::default()
+            .buffered_lines_limit(config.buffer_limit.max(100))
+            .finish(std::io::stdout());
+
         // Only use color if tracing output is being sent to a terminal or if it was explicitly
         // forced to.
         let use_color =
@@ -47,6 +69,7 @@ impl Tracing {
 
             let logger = FmtSubscriber::builder()
                 .with_ansi(use_color)
+                .with_writer(non_blocking)
                 .with_env_filter(&filter);
 
             // Enable reloading if that feature is selected.
@@ -82,6 +105,7 @@ impl Tracing {
             // Using `FmtSubscriber` as the base subscriber, all the logs get filtered.
             let logger = fmt::Layer::new()
                 .with_ansi(use_color)
+                .with_writer(non_blocking)
                 .with_filter(EnvFilter::from(&filter));
 
             let subscriber = subscriber.with(logger);
@@ -185,6 +209,7 @@ impl Tracing {
             initial_filter: filter,
             #[cfg(feature = "flamegraph")]
             flamegrapher,
+            _guard,
         })
     }
 

zebrad/src/config.rs

@@ -93,6 +93,12 @@ pub struct TracingSection {
     /// verification of every 1000th block.
     pub filter: Option<String>,
 
+    /// The buffer_limit size sets the number of log lines that can be queued by the tracing subscriber
+    /// to be written to stdout before logs are dropped.
+    ///
+    /// Defaults to 128,000 with a minimum of 100.
+    pub buffer_limit: usize,
+
     /// The address used for an ad-hoc RPC endpoint allowing dynamic control of the tracing filter.
     ///
     /// Install Zebra using `cargo install --features=filter-reload` to enable this config.
@@ -140,6 +146,7 @@ impl Default for TracingSection {
             use_color: true,
             force_use_color: false,
             filter: None,
+            buffer_limit: 128_000,
             endpoint_addr: None,
             flamegraph: None,
             use_journald: false,

zebrad/tests/acceptance.rs

@@ -1229,6 +1229,77 @@ async fn rpc_endpoint(parallel_cpu_threads: bool) -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn non_blocking_logger() -> Result<()> {
+    use futures::FutureExt;
+    use std::{sync::mpsc, time::Duration};
+
+    let rt = tokio::runtime::Runtime::new().unwrap();
+    let (done_tx, done_rx) = mpsc::channel();
+
+    let test_task_handle: tokio::task::JoinHandle<Result<()>> = rt.spawn(async move {
+        let _init_guard = zebra_test::init();
+
+        // Write a configuration that has RPC listen_addr set
+        // [Note on port conflict](#Note on port conflict)
+        let mut config = random_known_rpc_port_config(false)?;
+        config.tracing.filter = Some("trace".to_string());
+        config.tracing.buffer_limit = 100;
+        let zebra_rpc_address = config.rpc.listen_addr.unwrap();
+
+        let dir = testdir()?.with_config(&mut config)?;
+        let mut child = dir.spawn_child(args!["start"])?;
+        // Wait until port is open.
+        child.expect_stdout_line_matches(
+            format!("Opened RPC endpoint at {}", config.rpc.listen_addr.unwrap()).as_str(),
+        )?;
+
+        // Create an http client
+        let client = reqwest::Client::new();
+
+        // Most of Zebra's lines are 100-200 characters long, so 500 requests should print enough to fill the unix pipe,
+        // fill the channel that tracing logs are queued onto, and drop logs rather than block execution.
+        for _ in 0..500 {
+            let res = client
+                .post(format!("http://{}", &zebra_rpc_address))
+                .body(r#"{"jsonrpc":"1.0","method":"getinfo","params":[],"id":123}"#)
+                .header("Content-Type", "application/json")
+                .send()
+                .await?;
+
+            // Test that zebrad rpc endpoint is still responding to requests
+            assert!(res.status().is_success());
+        }
+
+        child.kill(false)?;
+
+        let output = child.wait_with_output()?;
+        let output = output.assert_failure()?;
+
+        // [Note on port conflict](#Note on port conflict)
+        output
+            .assert_was_killed()
+            .wrap_err("Possible port conflict. Are there other acceptance tests running?")?;
+
+        done_tx.send(())?;
+
+        Ok(())
+    });
+
+    // Wait until the spawned task finishes or return an error in 45 seconds
+    if done_rx.recv_timeout(Duration::from_secs(45)).is_err() {
+        return Err(eyre!("unexpected test task hang"));
+    }
+
+    rt.shutdown_timeout(Duration::from_secs(3));
+
+    match test_task_handle.now_or_never() {
+        Some(Ok(result)) => result,
+        Some(Err(error)) => Err(eyre!("join error: {:?}", error)),
+        None => Err(eyre!("unexpected test task hang")),
+    }
+}
+
 /// Make sure `lightwalletd` works with Zebra, when both their states are empty.
 ///
 /// This test only runs when the `ZEBRA_TEST_LIGHTWALLETD` env var is set.