Flush AsyncPoolSink on the current thread if tearing down

spdlog/Cargo.toml

@@ -80,6 +80,11 @@ tracing-appender = "=0.2.2"
 [build-dependencies]
 rustc_version = "0.4.0"
 
+[[test]]
+name = "global_async_pool_sink"
+harness = false
+required-features = ["multi-thread"]
+
 [[bench]]
 name = "compare_with_cpp_spdlog"
 harness = false

spdlog/src/lib.rs

@@ -647,13 +647,16 @@ pub fn log_crate_proxy() -> &'static LogCrateProxy {
     &PROXY
 }
 
+static IS_TEARING_DOWN: AtomicBool = AtomicBool::new(false);
+
 fn flush_default_logger_at_exit() {
     // Rust never calls `drop` for static variables.
     //
     // Setting up an exit handler gives us a chance to flush the default logger
     // once at the program exit, thus we don't lose the last logs.
 
     extern "C" fn handler() {
+        IS_TEARING_DOWN.store(true, Ordering::SeqCst);
         if let Some(default_logger) = DEFAULT_LOGGER.get() {
             default_logger.load().flush()
         }

spdlog/src/sink/async_sink/async_pool_sink.rs

@@ -78,9 +78,19 @@ impl Sink for AsyncPoolSink {
     }
 
     fn flush(&self) -> Result<()> {
-        self.assign_task(Task::Flush {
-            backend: self.clone_backend(),
-        })
+        if crate::IS_TEARING_DOWN.load(Ordering::SeqCst) {
+            // https://github.com/SpriteOvO/spdlog-rs/issues/64
+            //
+            // `crossbeam` uses thread-local internally, which is not supported in `atexit`
+            // callback. Let's directly flush the sinks on the current thread if the program
+            // is tearing down.
+            self.backend.flush();
+            Ok(())
+        } else {
+            self.assign_task(Task::Flush {
+                backend: self.clone_backend(),
+            })
+        }
     }
 
     /// For [`AsyncPoolSink`], the function performs the same call to all

spdlog/tests/global_async_pool_sink.rs

@@ -0,0 +1,133 @@
+use std::{
+    env,
+    fmt::Write,
+    os::raw::c_int,
+    process::{self, Stdio},
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
+};
+
+use spdlog::{
+    formatter::Formatter,
+    prelude::*,
+    sink::{AsyncPoolSink, Sink},
+    ErrorHandler,
+};
+
+static IS_FLUSHED: AtomicBool = AtomicBool::new(false);
+
+struct SetFlagSink;
+
+impl Sink for SetFlagSink {
+    fn log(&self, _record: &spdlog::Record) -> error::Result<()> {
+        Ok(())
+    }
+
+    fn flush(&self) -> error::Result<()> {
+        IS_FLUSHED.store(true, Ordering::SeqCst);
+        Ok(())
+    }
+
+    fn level_filter(&self) -> LevelFilter {
+        LevelFilter::All
+    }
+
+    fn set_level_filter(&self, _level_filter: LevelFilter) {
+        unimplemented!()
+    }
+
+    fn set_formatter(&self, _formatter: Box<dyn Formatter>) {
+        unimplemented!()
+    }
+
+    fn set_error_handler(&self, _handler: Option<ErrorHandler>) {
+        unimplemented!()
+    }
+}
+
+fn run_test() {
+    {
+        extern "C" fn check() {
+            // Assert that `AsyncPoolSink` in the default logger will be flushed correctly
+            // and will not panic.
+            assert!(IS_FLUSHED.load(Ordering::SeqCst));
+        }
+        // Setup `atexit` to check the flag at the end of the program
+        extern "C" {
+            fn atexit(cb: extern "C" fn()) -> c_int;
+        }
+        assert_eq!(unsafe { atexit(check) }, 0);
+
+        let async_pool_sink = Arc::new(
+            AsyncPoolSink::builder()
+                .sink(Arc::new(SetFlagSink))
+                .build()
+                .unwrap(),
+        );
+        let logger = Arc::new(
+            Logger::builder()
+                .sink(async_pool_sink)
+                .level_filter(LevelFilter::All)
+                .flush_level_filter(LevelFilter::Off)
+                .build()
+                .unwrap(),
+        );
+        spdlog::set_default_logger(logger);
+    }
+
+    info!("hello async_pool_sink");
+}
+
+fn main() {
+    // https://github.com/SpriteOvO/spdlog-rs/issues/64
+
+    // This is a flaky test, it only has a certain probability of failing, so we run
+    // it multiple times to make sure it's really working properly.
+    {
+        let mut captured_output = String::new();
+        let args = env::args().collect::<Vec<_>>();
+        // If this is the parent process (no additional arguments)
+        if args.len() == 1 {
+            for i in 0..1000 {
+                let output = process::Command::new(&args[0])
+                    .arg("child")
+                    .stderr(Stdio::piped())
+                    .output()
+                    .unwrap();
+                let success = output.status.success();
+
+                writeln!(
+                    captured_output,
+                    "Attempt #{i} = {}",
+                    if success { "ok" } else { "failed!" }
+                )
+                .unwrap();
+
+                if !success {
+                    eprintln!("{captured_output}");
+
+                    let stderr = String::from_utf8_lossy(&output.stderr).lines().fold(
+                        String::new(),
+                        |mut contents, line| {
+                            writeln!(&mut contents, "> {line}").unwrap();
+                            contents
+                        },
+                    );
+                    eprintln!("Stderr of the failed child:\n{stderr}");
+
+                    panic!("Test failed");
+                }
+            }
+            return;
+        } else {
+            assert_eq!(args[1], "child");
+        }
+
+        // Run the test after leaving the scope, so the main function ends
+        // without dropping additional variables, thus exiting faster. This
+        // should increase the probability of reproducing the error.
+    }
+    run_test();
+}