moonfire-nvr/src/dir.rs

693 lines
27 KiB
Rust

// This file is part of Moonfire NVR, a security camera digital video recorder.
// Copyright (C) 2016 Scott Lamb <slamb@slamb.org>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// In addition, as a special exception, the copyright holders give
// permission to link the code of portions of this program with the
// OpenSSL library under certain conditions as described in each
// individual source file, and distribute linked combinations including
// the two.
//
// You must obey the GNU General Public License in all respects for all
// of the code used other than OpenSSL. If you modify file(s) with this
// exception, you may extend this exception to your version of the
// file(s), but you are not obligated to do so. If you do not wish to do
// so, delete this exception statement from your version. If you delete
// this exception statement from all source files in the program, then
// also delete it here.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//! Sample file directory management.
//!
//! This includes opening files for serving, rotating away old files, and saving new files.
use db;
use error::Error;
use libc;
use recording;
use openssl::crypto::hash;
use std::cmp;
use std::ffi;
use std::fs;
use std::io::{self, Write};
use std::mem;
use std::os::unix::io::FromRawFd;
use std::sync::{Arc, Mutex, MutexGuard};
use std::sync::mpsc;
use std::thread;
use uuid::Uuid;
/// A sample file directory. This is currently a singleton in production. (Maybe in the future
/// Moonfire will be extended to support multiple directories on different spindles.)
///
/// If the directory is used for writing, the `start_syncer` function should be called to start
/// a background thread. This thread manages deleting files and writing new files. It synces the
/// directory and commits these operations to the database in the correct order to maintain the
/// invariants described in `design/schema.md`.
pub struct SampleFileDir {
db: Arc<db::Database>,
/// The open file descriptor for the directory. The worker uses it to create files and sync the
/// directory. Other threads use it to open sample files for reading during video serving.
fd: Fd,
// Lock order: don't acquire mutable.lock() while holding db.lock().
mutable: Mutex<SharedMutableState>,
}
/// A file descriptor associated with a directory (not necessarily the sample file dir).
pub struct Fd(libc::c_int);
impl Drop for Fd {
fn drop(&mut self) {
if unsafe { libc::close(self.0) } < 0 {
let e = io::Error::last_os_error();
warn!("Unable to close sample file dir: {}", e);
}
}
}
impl Fd {
/// Opens the given path as a directory.
pub fn open(path: &str) -> Result<Fd, io::Error> {
let cstring = ffi::CString::new(path)
.map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
let fd = unsafe { libc::open(cstring.as_ptr(), libc::O_DIRECTORY | libc::O_RDONLY, 0) };
if fd < 0 {
return Err(io::Error::last_os_error().into());
}
Ok(Fd(fd))
}
/// Locks the directory with the specified `flock` operation.
pub fn lock(&self, operation: libc::c_int) -> Result<(), io::Error> {
let ret = unsafe { libc::flock(self.0, operation) };
if ret < 0 {
return Err(io::Error::last_os_error().into());
}
Ok(())
}
}
impl SampleFileDir {
pub fn new(path: &str, db: Arc<db::Database>) -> Result<Arc<SampleFileDir>, Error> {
let fd = Fd::open(path)?;
Ok(Arc::new(SampleFileDir{
db: db,
fd: fd,
mutable: Mutex::new(SharedMutableState{
next_uuid: None,
}),
}))
}
/// Opens the given sample file for reading.
pub fn open_sample_file(&self, uuid: Uuid) -> Result<fs::File, io::Error> {
self.open_int(uuid, libc::O_RDONLY, 0)
}
/// Creates a new writer.
/// Note this doesn't wait for previous rotation to complete; it's assumed the sample file
/// directory has sufficient space for a couple recordings per camera in addition to the
/// cameras' total `retain_bytes`.
///
/// The new recording will continue from `prev` if specified; this should be as returned from
/// a previous `close` call.
pub fn create_writer<'a>(&self, channel: &'a SyncerChannel, prev: Option<PreviousWriter>,
camera_id: i32, video_sample_entry_id: i32)
-> Result<Writer<'a>, Error> {
// Grab the next uuid. Typically one is cached—a sync has usually completed since the last
// writer was created, and syncs ensure `next_uuid` is filled while performing their
// transaction. But if not, perform an extra database transaction to reserve a new one.
let uuid = match self.mutable.lock().unwrap().next_uuid.take() {
Some(u) => u,
None => {
info!("Committing extra transaction because there's no cached uuid");
let mut db = self.db.lock();
let mut tx = db.tx()?;
let u = tx.reserve_sample_file()?;
tx.commit()?;
u
},
};
let f = match self.open_int(uuid, libc::O_WRONLY | libc::O_EXCL | libc::O_CREAT, 0o600) {
Ok(f) => f,
Err(e) => {
self.mutable.lock().unwrap().next_uuid = Some(uuid);
return Err(e.into());
},
};
Writer::open(f, uuid, prev, camera_id, video_sample_entry_id, channel)
}
/// Opens a sample file within this directory with the given flags and (if creating) mode.
fn open_int(&self, uuid: Uuid, flags: libc::c_int, mode: libc::c_int)
-> Result<fs::File, io::Error> {
let p = SampleFileDir::get_rel_pathname(uuid);
let fd = unsafe { libc::openat(self.fd.0, p.as_ptr(), flags, mode) };
if fd < 0 {
return Err(io::Error::last_os_error())
}
unsafe { Ok(fs::File::from_raw_fd(fd)) }
}
/// Gets a pathname for a sample file suitable for passing to open or unlink.
fn get_rel_pathname(uuid: Uuid) -> [libc::c_char; 37] {
let mut buf = [0u8; 37];
write!(&mut buf[..36], "{}", uuid.hyphenated()).expect("can't format uuid to pathname buf");
// libc::c_char seems to be i8 on some platforms (Linux/arm) and u8 on others (Linux/amd64).
// Transmute, suppressing the warning that happens on platforms in which it's already u8.
#[allow(useless_transmute)]
unsafe { mem::transmute::<[u8; 37], [libc::c_char; 37]>(buf) }
}
/// Unlinks the given sample file within this directory.
fn unlink(fd: &Fd, uuid: Uuid) -> Result<(), io::Error> {
let p = SampleFileDir::get_rel_pathname(uuid);
let res = unsafe { libc::unlinkat(fd.0, p.as_ptr(), 0) };
if res < 0 {
return Err(io::Error::last_os_error())
}
Ok(())
}
/// Syncs the directory itself.
fn sync(&self) -> Result<(), io::Error> {
let res = unsafe { libc::fsync(self.fd.0) };
if res < 0 {
return Err(io::Error::last_os_error())
};
Ok(())
}
}
/// State shared between users of the `SampleFileDirectory` struct and the syncer.
struct SharedMutableState {
next_uuid: Option<Uuid>,
}
/// A command sent to the syncer. These correspond to methods in the `SyncerChannel` struct.
enum SyncerCommand {
AsyncSaveRecording(db::RecordingToInsert, fs::File),
AsyncAbandonRecording(Uuid),
#[cfg(test)]
Flush(mpsc::SyncSender<()>),
}
/// A channel which can be used to send commands to the syncer.
/// Can be cloned to allow multiple threads to send commands.
#[derive(Clone)]
pub struct SyncerChannel(mpsc::Sender<SyncerCommand>);
/// State of the worker thread.
struct SyncerState {
dir: Arc<SampleFileDir>,
to_unlink: Vec<Uuid>,
to_mark_deleted: Vec<Uuid>,
cmds: mpsc::Receiver<SyncerCommand>,
}
/// Starts a syncer for the given sample file directory.
/// There should be only one syncer per directory, or 0 if operating in read-only mode.
/// This function will perform the initial rotation synchronously, so that it is finished before
/// file writing starts. Afterward the syncing happens in a background thread.
///
/// Returns a `SyncerChannel` which can be used to send commands (and can be cloned freely) and
/// a `JoinHandle` for the syncer thread. At program shutdown, all `SyncerChannel` clones should be
/// removed and then the handle joined to allow all recordings to be persisted.
pub fn start_syncer(dir: Arc<SampleFileDir>)
-> Result<(SyncerChannel, thread::JoinHandle<()>), Error> {
let to_unlink = dir.db.lock().list_reserved_sample_files()?;
let (snd, rcv) = mpsc::channel();
let mut state = SyncerState {
dir: dir,
to_unlink: to_unlink,
to_mark_deleted: Vec::new(),
cmds: rcv,
};
state.initial_rotation()?;
Ok((SyncerChannel(snd),
thread::Builder::new().name("syncer".into()).spawn(move || state.run()).unwrap()))
}
impl SyncerChannel {
/// Asynchronously syncs the given writer, closes it, records it into the database, and
/// starts rotation.
fn async_save_recording(&self, recording: db::RecordingToInsert, f: fs::File) {
self.0.send(SyncerCommand::AsyncSaveRecording(recording, f)).unwrap();
}
fn async_abandon_recording(&self, uuid: Uuid) {
self.0.send(SyncerCommand::AsyncAbandonRecording(uuid)).unwrap();
}
/// For testing: flushes the syncer, waiting for all currently-queued commands to complete.
#[cfg(test)]
pub fn flush(&self) {
let (snd, rcv) = mpsc::sync_channel(0);
self.0.send(SyncerCommand::Flush(snd)).unwrap();
rcv.recv().unwrap_err(); // syncer should just drop the channel, closing it.
}
}
impl SyncerState {
fn run(&mut self) {
loop {
match self.cmds.recv() {
Err(_) => return, // all senders have closed the channel; shutdown
Ok(SyncerCommand::AsyncSaveRecording(recording, f)) => self.save(recording, f),
Ok(SyncerCommand::AsyncAbandonRecording(uuid)) => self.abandon(uuid),
#[cfg(test)]
Ok(SyncerCommand::Flush(_)) => {}, // just drop the supplied sender, closing it.
};
}
}
/// Rotates files for all cameras and deletes stale reserved uuids from previous runs.
fn initial_rotation(&mut self) -> Result<(), Error> {
let mut to_delete = Vec::new();
{
let mut db = self.dir.db.lock();
for (camera_id, camera) in db.cameras_by_id() {
self.get_rows_to_delete(&db, *camera_id, camera, 0, &mut to_delete)?;
}
let mut tx = db.tx()?;
tx.delete_recordings(&to_delete)?;
tx.commit()?;
}
for row in to_delete {
self.to_unlink.push(row.uuid);
}
self.try_unlink();
if !self.to_unlink.is_empty() {
return Err(Error::new(format!("failed to unlink {} sample files",
self.to_unlink.len())));
}
self.dir.sync()?;
{
let mut db = self.dir.db.lock();
let mut tx = db.tx()?;
tx.mark_sample_files_deleted(&self.to_mark_deleted)?;
tx.commit()?;
}
self.to_mark_deleted.clear();
Ok(())
}
/// Saves the given recording and causes rotation to happen.
/// Note that part of rotation is deferred for the next cycle (saved writing or program startup)
/// so that there can be only one dir sync and database transaction per save.
fn save(&mut self, recording: db::RecordingToInsert, f: fs::File) {
if let Err(e) = self.save_helper(&recording, f) {
error!("camera {}: will discard recording {} due to error while saving: {}",
recording.camera_id, recording.sample_file_uuid, e);
self.to_unlink.push(recording.sample_file_uuid);
return;
}
}
fn abandon(&mut self, uuid: Uuid) {
self.to_unlink.push(uuid);
self.try_unlink();
}
/// Internal helper for `save`. This is separated out so that the question-mark operator
/// can be used in the many error paths.
fn save_helper(&mut self, recording: &db::RecordingToInsert, f: fs::File)
-> Result<(), Error> {
self.try_unlink();
if !self.to_unlink.is_empty() {
return Err(Error::new(format!("failed to unlink {} files.", self.to_unlink.len())));
}
f.sync_all()?;
self.dir.sync()?;
let mut to_delete = Vec::new();
let mut l = self.dir.mutable.lock().unwrap();
let mut db = self.dir.db.lock();
let mut new_next_uuid = l.next_uuid;
{
let camera =
db.cameras_by_id().get(&recording.camera_id)
.ok_or_else(|| Error::new(format!("no such camera {}", recording.camera_id)))?;
self.get_rows_to_delete(&db, recording.camera_id, camera,
recording.sample_file_bytes as i64, &mut to_delete)?;
}
let mut tx = db.tx()?;
tx.mark_sample_files_deleted(&self.to_mark_deleted)?;
tx.delete_recordings(&to_delete)?;
if new_next_uuid.is_none() {
new_next_uuid = Some(tx.reserve_sample_file()?);
}
tx.insert_recording(recording)?;
tx.commit()?;
l.next_uuid = new_next_uuid;
self.to_mark_deleted.clear();
self.to_unlink.extend(to_delete.iter().map(|row| row.uuid));
Ok(())
}
/// Gets rows to delete to bring a camera's disk usage within bounds.
fn get_rows_to_delete(&self, db: &MutexGuard<db::LockedDatabase>, camera_id: i32,
camera: &db::Camera, extra_bytes_needed: i64,
to_delete: &mut Vec<db::ListOldestSampleFilesRow>) -> Result<(), Error> {
let bytes_needed = camera.sample_file_bytes + extra_bytes_needed - camera.retain_bytes;
let mut bytes_to_delete = 0;
if bytes_needed <= 0 {
debug!("{}: have remaining quota of {}", camera.short_name, -bytes_needed);
return Ok(());
}
let mut n = 0;
db.list_oldest_sample_files(camera_id, |row| {
bytes_to_delete += row.sample_file_bytes as i64;
to_delete.push(row);
n += 1;
bytes_needed > bytes_to_delete // continue as long as more deletions are needed.
})?;
if bytes_needed > bytes_to_delete {
return Err(Error::new(format!("{}: couldn't find enough files to delete: {} left.",
camera.short_name, bytes_needed)));
}
info!("{}: deleting {} bytes in {} recordings ({} bytes needed)",
camera.short_name, bytes_to_delete, n, bytes_needed);
Ok(())
}
/// Tries to unlink all the uuids in `self.to_unlink`. Any which can't be unlinked will
/// be retained in the vec.
fn try_unlink(&mut self) {
let to_mark_deleted = &mut self.to_mark_deleted;
let fd = &self.dir.fd;
self.to_unlink.retain(|uuid| {
if let Err(e) = SampleFileDir::unlink(fd, *uuid) {
if e.kind() == io::ErrorKind::NotFound {
warn!("dir: Sample file {} already deleted!", uuid.hyphenated());
to_mark_deleted.push(*uuid);
false
} else {
warn!("dir: Unable to unlink {}: {}", uuid.hyphenated(), e);
true
}
} else {
to_mark_deleted.push(*uuid);
false
}
});
}
}
/// Single-use struct to write a single recording to disk and commit its metadata to the database.
/// Use `SampleFileDir::create_writer` to create a new writer. `Writer` hands off its state to the
/// syncer when done. It either saves the recording to the database (if I/O errors do not prevent
/// this) or marks it as abandoned so that the syncer will attempt to unlink the file.
pub struct Writer<'a>(Option<InnerWriter<'a>>);
/// The state associated with a `Writer`. The indirection is for the `Drop` trait; `close` moves
/// `f` and `index.video_index` out of the `InnerWriter`, which is not allowed on a struct with
/// a `Drop` trait. To avoid this problem, the real state is surrounded by an `Option`. The
/// `Option` should none only after close is called, and thus never in a way visible to callers.
struct InnerWriter<'a> {
syncer_channel: &'a SyncerChannel,
f: fs::File,
index: recording::SampleIndexEncoder,
uuid: Uuid,
corrupt: bool,
hasher: hash::Hasher,
/// The end time of the previous segment in this run, if any.
prev_end: Option<recording::Time>,
/// The start time of this segment, based solely on examining the local clock after frames in
/// this segment were received. Frames can suffer from various kinds of delay (initial
/// buffering, encoding, and network transmission), so this time is set to far in the future on
/// construction, given a real value on the first packet, and decreased as less-delayed packets
/// are discovered. See design/time.md for details.
local_start: recording::Time,
adjuster: ClockAdjuster,
camera_id: i32,
video_sample_entry_id: i32,
run_offset: i32,
/// A sample which has been written to disk but not added to `index`. Index writes are one
/// sample behind disk writes because the duration of a sample is the difference between its
/// pts and the next sample's pts. A sample is flushed when the next sample is written, when
/// the writer is closed cleanly (the caller supplies the next pts), or when the writer is
/// closed uncleanly (with a zero duration, which the `.mp4` format allows only at the end).
unflushed_sample: Option<UnflushedSample>,
}
/// Adjusts durations given by the camera to correct its clock frequency error.
struct ClockAdjuster {
/// Every `every_minus_1 + 1` units, add `-ndir`.
/// Note i32::max_value() disables adjustment.
every_minus_1: i32,
/// Should be 1 or -1 (unless disabled).
ndir: i32,
/// Keeps accumulated difference from previous values.
cur: i32,
}
impl ClockAdjuster {
fn new(local_time_delta: Option<i64>) -> Self {
// Pick an adjustment rate to correct local_time_delta over the next minute (the
// desired duration of a single recording). Cap the rate at 500 ppm (which corrects
// 2,700/90,000ths of a second over a minute) to prevent noticeably speeding up or slowing
// down playback.
let (every, ndir) = match local_time_delta {
None | Some(0) => (i32::max_value(), 0),
Some(d) if d <= -2700 => (2000, 1),
Some(d) if d >= 2700 => (2000, -1),
Some(d) if d < -60 => ((60 * 90000) / -(d as i32), 1),
Some(d) => ((60 * 90000) / (d as i32), -1),
};
ClockAdjuster{
every_minus_1: every - 1,
ndir: ndir,
cur: 0,
}
}
fn adjust(&mut self, mut val: i32) -> i32 {
self.cur += val;
// The "val > self.ndir" here is so that if decreasing durations (ndir == 1), we don't
// cause a duration of 1 to become a duration of 0. It has no effect when increasing
// durations. (There's no danger of a duration of 0 becoming a duration of 1; cur wouldn't
// be newly > self.every_minus_1.)
while self.cur > self.every_minus_1 && val > self.ndir {
val -= self.ndir;
self.cur -= self.every_minus_1 + 1;
}
val
}
}
struct UnflushedSample {
local_time: recording::Time,
pts_90k: i64,
len: i32,
is_key: bool,
}
#[derive(Copy, Clone)]
pub struct PreviousWriter {
end_time: recording::Time,
local_time_delta: recording::Duration,
run_offset: i32,
}
impl<'a> Writer<'a> {
/// Opens the writer; for use by `SampleFileDir` (which should supply `f`).
fn open(f: fs::File, uuid: Uuid, prev: Option<PreviousWriter>, camera_id: i32,
video_sample_entry_id: i32, syncer_channel: &'a SyncerChannel) -> Result<Self, Error> {
Ok(Writer(Some(InnerWriter{
syncer_channel: syncer_channel,
f: f,
index: recording::SampleIndexEncoder::new(),
uuid: uuid,
corrupt: false,
hasher: hash::Hasher::new(hash::Type::SHA1)?,
prev_end: prev.map(|p| p.end_time),
local_start: recording::Time(i64::max_value()),
adjuster: ClockAdjuster::new(prev.map(|p| p.local_time_delta.0)),
camera_id: camera_id,
video_sample_entry_id: video_sample_entry_id,
run_offset: prev.map(|p| p.run_offset + 1).unwrap_or(0),
unflushed_sample: None,
})))
}
/// Writes a new frame to this segment.
/// `local_time` should be the local clock's time as of when this packet was received.
pub fn write(&mut self, pkt: &[u8], local_time: recording::Time, pts_90k: i64,
is_key: bool) -> Result<(), Error> {
let w = self.0.as_mut().unwrap();
if let Some(unflushed) = w.unflushed_sample.take() {
let duration = (pts_90k - unflushed.pts_90k) as i32;
if duration <= 0 {
return Err(Error::new(format!("pts not monotonically increasing; got {} then {}",
unflushed.pts_90k, pts_90k)));
}
let duration = w.adjuster.adjust(duration);
w.index.add_sample(duration, unflushed.len, unflushed.is_key);
w.extend_local_start(unflushed.local_time);
}
let mut remaining = pkt;
while !remaining.is_empty() {
let written = match w.f.write(remaining) {
Ok(b) => b,
Err(e) => {
if remaining.len() < pkt.len() {
// Partially written packet. Truncate if possible.
if let Err(e2) = w.f.set_len(w.index.sample_file_bytes as u64) {
error!("After write to {} failed with {}, truncate failed with {}; \
sample file is corrupt.", w.uuid.hyphenated(), e, e2);
w.corrupt = true;
}
}
return Err(Error::from(e));
},
};
remaining = &remaining[written..];
}
w.unflushed_sample = Some(UnflushedSample{
local_time: local_time,
pts_90k: pts_90k,
len: pkt.len() as i32,
is_key: is_key});
w.hasher.update(pkt)?;
Ok(())
}
/// Cleanly closes the writer, using a supplied pts of the next sample for the last sample's
/// duration (if known). If `close` is not called, the `Drop` trait impl will close the trait,
/// swallowing errors and using a zero duration for the last sample.
pub fn close(mut self, next_pts: Option<i64>) -> Result<PreviousWriter, Error> {
self.0.take().unwrap().close(next_pts)
}
}
impl<'a> InnerWriter<'a> {
fn extend_local_start(&mut self, pkt_local_time: recording::Time) {
let new = pkt_local_time - recording::Duration(self.index.total_duration_90k as i64);
self.local_start = cmp::min(self.local_start, new);
}
fn close(mut self, next_pts: Option<i64>) -> Result<PreviousWriter, Error> {
if self.corrupt {
self.syncer_channel.async_abandon_recording(self.uuid);
return Err(Error::new(format!("recording {} is corrupt", self.uuid)));
}
let unflushed =
self.unflushed_sample.take().ok_or_else(|| Error::new("no packets!".to_owned()))?;
let duration = self.adjuster.adjust(match next_pts {
None => 0,
Some(p) => (p - unflushed.pts_90k) as i32,
});
self.index.add_sample(duration, unflushed.len, unflushed.is_key);
self.extend_local_start(unflushed.local_time);
let mut sha1_bytes = [0u8; 20];
sha1_bytes.copy_from_slice(&self.hasher.finish()?[..]);
let start = self.prev_end.unwrap_or(self.local_start);
let end = start + recording::Duration(self.index.total_duration_90k as i64);
let flags = if self.index.has_trailing_zero() { db::RecordingFlags::TrailingZero as i32 }
else { 0 };
let local_start_delta = self.local_start - start;
let recording = db::RecordingToInsert{
camera_id: self.camera_id,
sample_file_bytes: self.index.sample_file_bytes,
time: start .. end,
local_time_delta: local_start_delta,
video_samples: self.index.video_samples,
video_sync_samples: self.index.video_sync_samples,
video_sample_entry_id: self.video_sample_entry_id,
sample_file_uuid: self.uuid,
video_index: self.index.video_index,
sample_file_sha1: sha1_bytes,
run_offset: self.run_offset,
flags: flags,
};
self.syncer_channel.async_save_recording(recording, self.f);
Ok(PreviousWriter{
end_time: end,
local_time_delta: local_start_delta,
run_offset: self.run_offset,
})
}
}
impl<'a> Drop for Writer<'a> {
fn drop(&mut self) {
if let Some(w) = self.0.take() {
// Swallow any error. The caller should only drop the Writer without calling close()
// if there's already been an error. The caller should report that. No point in
// complaining again.
let _ = w.close(None);
}
}
}
#[cfg(test)]
mod tests {
use super::ClockAdjuster;
use testutil;
#[test]
fn adjust() {
testutil::init();
// no-ops.
let mut a = ClockAdjuster::new(None);
for _ in 0..1800 {
assert_eq!(3000, a.adjust(3000));
}
a = ClockAdjuster::new(Some(0));
for _ in 0..1800 {
assert_eq!(3000, a.adjust(3000));
}
// typical, 100 ppm adjustment.
a = ClockAdjuster::new(Some(-540));
let mut total = 0;
for _ in 0..1800 {
let new = a.adjust(3000);
assert!(new == 2999 || new == 3000);
total += new;
}
let expected = 1800*3000 - 540;
assert!(total == expected || total == expected + 1, "total={} vs expected={}",
total, expected);
// capped at 500 ppm (change of 2,700/90,000ths over 1 minute).
a = ClockAdjuster::new(Some(-1_000_000));
total = 0;
for _ in 0..1800 {
let new = a.adjust(3000);
assert!(new == 2998 || new == 2999, "new={}", new);
total += new;
}
let expected = 1800*3000 - 2700;
assert!(total == expected || total == expected + 1, "total={} vs expected={}",
total, expected);
}
}