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Subject: [pdm-devel] [PATCH proxmox-datacenter-manager v4 3/6] remote tasks:
improve locking for task archive iterator
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Instead of awkwardly using into_lock for keeping the archive locked,
pass the lock as a reference to TaskCache::get_tasks_with_lock. The
iterator itself only holds the lock if get use the auto-locking
TaskCache::get_tasks, otherwise we ensure that the lock lives long
enough via lifetimes and PhantomData in the iterator.
Suggested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
---
Notes:
New in v3
Changes since v3:
- remove unecessary (and potentially unsafe) pub for get_tasks_impl
(copy/paste mistake)
server/src/remote_tasks/mod.rs | 2 +-
server/src/remote_tasks/task_cache.rs | 62 +++++++++++++--------------
2 files changed, 31 insertions(+), 33 deletions(-)
diff --git a/server/src/remote_tasks/mod.rs b/server/src/remote_tasks/mod.rs
index 126c9ad3..b0fc052f 100644
--- a/server/src/remote_tasks/mod.rs
+++ b/server/src/remote_tasks/mod.rs
@@ -24,7 +24,7 @@ pub async fn get_tasks(filters: TaskFilters) -> Result<Vec<TaskListItem>, Error>
GetTasks::All
};
- for task in &mut cache
+ for task in cache
.get_tasks(which)?
.skip(filters.start as usize)
.take(filters.limit as usize)
diff --git a/server/src/remote_tasks/task_cache.rs b/server/src/remote_tasks/task_cache.rs
index f8dd821e..6e85f10a 100644
--- a/server/src/remote_tasks/task_cache.rs
+++ b/server/src/remote_tasks/task_cache.rs
@@ -6,6 +6,7 @@ use std::{
fs::File,
io::{BufRead, BufReader, BufWriter, ErrorKind, Lines, Write},
iter::Peekable,
+ marker::PhantomData,
path::{Path, PathBuf},
time::Duration,
};
@@ -213,8 +214,8 @@ impl TaskCache {
.map(|(remote, add_tasks)| (remote, add_tasks.update_most_recent_archive_timestamp))
.collect();
- let mut task_iter = self
- .get_tasks_with_lock(GetTasks::Active, lock)
+ let task_iter = self
+ .get_tasks_with_lock(GetTasks::Active, &lock)
.context("failed to create archive iterator for active tasks")?;
let mut active_tasks =
@@ -226,10 +227,6 @@ impl TaskCache {
}
}));
- // Consume the iterator to get back the lock. The lock is held
- // until _lock is finally dropped at the end of the function.
- let _lock = task_iter.into_lock();
-
let mut new_finished_tasks = Vec::new();
for task in tasks {
@@ -387,7 +384,7 @@ impl TaskCache {
let mut tasks = Vec::new();
let mut task_iter = self
- .get_tasks_with_lock(GetTasks::Active, lock)
+ .get_tasks_with_lock(GetTasks::Active, &lock)
.context("failed to create active task iterator")?;
for task in &mut task_iter {
@@ -404,8 +401,6 @@ impl TaskCache {
tasks.push(task.clone());
tasks.sort_by(compare_tasks_reverse);
- let _lock = task_iter.into_lock();
-
let mut state = self.read_state();
state
@@ -432,24 +427,28 @@ impl TaskCache {
///
/// This function will request a non-exclusive read-lock, don't call if
/// you already hold a lock for this cache. See [`Self::get_tasks_with_lock`].
- pub fn get_tasks(&self, mode: GetTasks) -> Result<TaskArchiveIterator, Error> {
- let lock = self
- .lock(false)
- .context("get_tasks: failed to acquire lock")?;
- self.get_tasks_with_lock(mode, lock)
+ pub fn get_tasks(&self, mode: GetTasks) -> Result<TaskArchiveIterator<'static>, Error> {
+ let lock = self.lock(false).context("failed to lock archive")?;
+ self.get_tasks_impl(mode, Some(lock))
.context("failed to create task archive iterator")
}
/// Iterate over cached tasks.
///
- /// This function requires you to pass a lock. If you want to continue to hold the lock
- /// after iterating, you can consume the iterator by calling
- /// [`TaskArchiveIterator::into_lock`], yielding the original lock.
- pub fn get_tasks_with_lock(
+ /// This function requires you to pass a lock.
+ pub fn get_tasks_with_lock<'a>(
&self,
mode: GetTasks,
- lock: TaskCacheLock,
- ) -> Result<TaskArchiveIterator, Error> {
+ _lock: &'a TaskCacheLock,
+ ) -> Result<TaskArchiveIterator<'a>, Error> {
+ self.get_tasks_impl(mode, None)
+ }
+
+ fn get_tasks_impl<'a>(
+ &self,
+ mode: GetTasks,
+ lock: Option<TaskCacheLock>,
+ ) -> Result<TaskArchiveIterator<'a>, Error> {
match mode {
GetTasks::All => {
let archive_files = self.archive_files()?.into_iter().map(|pair| pair.file);
@@ -682,32 +681,31 @@ pub fn compare_tasks_reverse(a: &TaskCacheItem, b: &TaskCacheItem) -> Ordering {
}
/// Iterator over the task archive.
-pub struct TaskArchiveIterator {
+pub struct TaskArchiveIterator<'a> {
/// Archive files to read.
files: Box<dyn Iterator<Item = PathBuf>>,
/// Archive iterator we are currently using, if any
current: Option<ArchiveIterator<BufReader<File>>>,
- /// Lock for this archive.
- lock: TaskCacheLock,
+ /// Lock for this archive. This contains the lock in case we
+ /// need to keep the archive locked while iterating over it.
+ _lock: Option<TaskCacheLock>,
+ /// PhantomData to bind the lifetime of the iterator to an externally held lock.
+ _lifetime: PhantomData<&'a ()>,
}
-impl TaskArchiveIterator {
+impl TaskArchiveIterator<'_> {
/// Create a new task archive iterator.
- pub fn new(files: Box<dyn Iterator<Item = PathBuf>>, lock: TaskCacheLock) -> Self {
+ pub fn new(files: Box<dyn Iterator<Item = PathBuf>>, lock: Option<TaskCacheLock>) -> Self {
Self {
files,
current: None,
- lock,
+ _lock: lock,
+ _lifetime: PhantomData,
}
}
-
- /// Return the task archive lock, consuming `self`.
- pub fn into_lock(self) -> TaskCacheLock {
- self.lock
- }
}
-impl Iterator for &mut TaskArchiveIterator {
+impl Iterator for TaskArchiveIterator<'_> {
type Item = Result<TaskCacheItem, Error>;
fn next(&mut self) -> Option<Self::Item> {
--
2.39.5
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