gallery/src/nblog.rs

//! Non-blocking logger (Android). `log` calls on the UI thread must NEVER
//! block: logd-pipe backpressure during bursts was observed to block the
//! UI thread 10–40 ms (docs/BUGS/scroll-jank-120hz.md). Records are
//! formatted at the call site, pushed into a bounded channel; a drain
//! thread does the real `__android_log_write` and DROPS records when
//! saturated.
//!
//! `framelog`: FR lines are also mirrored to
//! /sdcard/Download/.gallery_perf.log — the logcat ring buffer rotates
//! every few seconds, which destroys the gap analysis. tools/fr_capture.py
//! pulls this file.

#[cfg(target_os = "android")]
pub mod android {
    use std::io::Write as _;
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::mpsc;
    use log::{Level, Log, Metadata, Record};

    extern "C" {
        fn __android_log_write(prio: i32, tag: *const u8, msg: *const u8) -> i32;
    }
    const TAG: &[u8] = b"gallery\0";
    const PERF_PATH: &str = "/sdcard/Download/.gallery_perf.log";

    fn perf_line(msg: &str) -> bool {
        msg.starts_with("FR ") || msg.starts_with("PERF ")
            || msg.starts_with("gallery: [W")
    }

    pub struct Logger {
        tx: mpsc::SyncSender<(i32, String)>,
        dropped: AtomicUsize,
    }

    pub fn init() {
        let (tx, rx) = mpsc::sync_channel::<(i32, String)>(4096);
        std::thread::Builder::new()
            .name("log-drain".into())
            .spawn(move || {
                // Opened lazily (MANAGE_EXTERNAL_STORAGE may be granted
                // later); retried until it works.
                let mut perf: Option<std::io::BufWriter<std::fs::File>> = None;
                let mut n = 0usize;
                for (prio, msg) in rx {
                    if cfg!(feature = "framelog") && perf_line(&msg) {
                        if perf.is_none() {
                            if let Ok(f) = std::fs::OpenOptions::new()
                                .create(true)
                                .append(true)
                                .open(PERF_PATH)
                            {
                                perf = Some(std::io::BufWriter::new(f));
                            }
                        }
                        if let Some(w) = perf.as_mut() {
                            let _ = w.write_all(msg.as_bytes());
                            let _ = w.write_all(b"\n");
                            n += 1;
                            if n >= 32 {
                                let _ = w.flush();
                                n = 0;
                            }
                        }
                    }
                    let b = msg.into_bytes();
                    let end = b.iter().position(|&c| c == 0).unwrap_or(b.len());
                    let mut safe: Vec<u8> = b[..end].iter().copied().filter(|&c| c != b'\n').collect();
                    safe.push(0);
                    unsafe {
                        __android_log_write(prio, TAG.as_ptr(), safe.as_ptr());
                    }
                }
            })
            .ok();
        let logger = Logger { tx, dropped: AtomicUsize::new(0) };
        let _ = log::set_boxed_logger(Box::new(logger)).map(|()| log::set_max_level(log::LevelFilter::Info));
    }

    impl Logger {
        fn prio(l: Level) -> i32 {
            match l {
                Level::Error => 6,
                Level::Warn => 5,
                Level::Info => 4,
                _ => 3,
            }
        }
    }

    impl Log for Logger {
        fn enabled(&self, m: &Metadata) -> bool {
            m.level() <= Level::Info
        }
        fn log(&self, record: &Record) {
            if !self.enabled(record.metadata()) {
                return;
            }
            let mut s = String::with_capacity(96);
            use std::fmt::Write as _;
            let _ = write!(&mut s, "{}", record.args());
            if self.tx.try_send((Self::prio(record.level()), s)).is_err() {
                self.dropped.fetch_add(1, Ordering::Relaxed);
            }
        }
        fn flush(&self) {}
    }
}

#[cfg(not(target_os = "android"))]
pub fn init() {
    // Desktop: the binary installs its own minimal logger.
}