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Revert "Use tokio locks in VirtualFile and turn with_file into macro (#…
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…5247)"

This reverts commit 76cc873.
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@problame
problame committed Sep 12, 2023
1 parent fa8f292 commit f781df5
Showing 1 changed file with 56 additions and 94 deletions.
150 changes: 56 additions & 94 deletions pageserver/src/virtual_file.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,7 @@ use std::io::{Error, ErrorKind, Seek, SeekFrom};
use std::os::unix::fs::FileExt;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use tokio::sync::{RwLock, RwLockReadGuard, RwLockWriteGuard};
use tokio::time::Instant;
use std::sync::{RwLock, RwLockWriteGuard};

///
/// A virtual file descriptor. You can use this just like std::fs::File, but internally
Expand Down Expand Up @@ -111,7 +110,7 @@ impl OpenFiles {
///
/// On return, we hold a lock on the slot, and its 'tag' has been updated
/// recently_used has been set. It's all ready for reuse.
async fn find_victim_slot(&self) -> (SlotHandle, RwLockWriteGuard<SlotInner>) {
fn find_victim_slot(&self) -> (SlotHandle, RwLockWriteGuard<SlotInner>) {
//
// Run the clock algorithm to find a slot to replace.
//
Expand Down Expand Up @@ -143,7 +142,7 @@ impl OpenFiles {
}
retries += 1;
} else {
slot_guard = slot.inner.write().await;
slot_guard = slot.inner.write().unwrap();
index = next;
break;
}
Expand Down Expand Up @@ -209,19 +208,6 @@ impl CrashsafeOverwriteError {
}
}

macro_rules! with_file {
($this:expr, $op:expr, | $ident:ident | $($body:tt)*) => {{
let $ident = $this.lock_file().await?;
let instant = Instant::now();
let result = $($body)*;
let elapsed = instant.elapsed().as_secs_f64();
STORAGE_IO_TIME_METRIC
.get($op)
.observe(elapsed);
result
}};
}

impl VirtualFile {
/// Open a file in read-only mode. Like File::open.
pub async fn open(path: &Path) -> Result<VirtualFile, std::io::Error> {
Expand Down Expand Up @@ -258,7 +244,7 @@ impl VirtualFile {
tenant_id = "*".to_string();
timeline_id = "*".to_string();
}
let (handle, mut slot_guard) = get_open_files().find_victim_slot().await;
let (handle, mut slot_guard) = get_open_files().find_victim_slot();

let file = STORAGE_IO_TIME_METRIC
.get(StorageIoOperation::Open)
Expand Down Expand Up @@ -345,24 +331,22 @@ impl VirtualFile {

/// Call File::sync_all() on the underlying File.
pub async fn sync_all(&self) -> Result<(), Error> {
with_file!(self, StorageIoOperation::Fsync, |file| file
.as_ref()
.sync_all())
self.with_file(StorageIoOperation::Fsync, |file| file.sync_all())
.await?
}

pub async fn metadata(&self) -> Result<fs::Metadata, Error> {
with_file!(self, StorageIoOperation::Metadata, |file| file
.as_ref()
.metadata())
self.with_file(StorageIoOperation::Metadata, |file| file.metadata())
.await?
}

/// Helper function internal to `VirtualFile` that looks up the underlying File,
/// opens it and evicts some other File if necessary. The passed parameter is
/// assumed to be a function available for the physical `File`.
///
/// We are doing it via a macro as Rust doesn't support async closures that
/// take on parameters with lifetimes.
async fn lock_file(&self) -> Result<FileGuard<'_>, Error> {
/// Helper function that looks up the underlying File for this VirtualFile,
/// opening it and evicting some other File if necessary. It calls 'func'
/// with the physical File.
async fn with_file<F, R>(&self, op: StorageIoOperation, mut func: F) -> Result<R, Error>
where
F: FnMut(&File) -> R,
{
let open_files = get_open_files();

let mut handle_guard = {
Expand All @@ -372,23 +356,27 @@ impl VirtualFile {
// We only need to hold the handle lock while we read the current handle. If
// another thread closes the file and recycles the slot for a different file,
// we will notice that the handle we read is no longer valid and retry.
let mut handle = *self.handle.read().await;
let mut handle = *self.handle.read().unwrap();
loop {
// Check if the slot contains our File
{
let slot = &open_files.slots[handle.index];
let slot_guard = slot.inner.read().await;
if slot_guard.tag == handle.tag && slot_guard.file.is_some() {
// Found a cached file descriptor.
slot.recently_used.store(true, Ordering::Relaxed);
return Ok(FileGuard { slot_guard });
let slot_guard = slot.inner.read().unwrap();
if slot_guard.tag == handle.tag {
if let Some(file) = &slot_guard.file {
// Found a cached file descriptor.
slot.recently_used.store(true, Ordering::Relaxed);
return Ok(STORAGE_IO_TIME_METRIC
.get(op)
.observe_closure_duration(|| func(file)));
}
}
}

// The slot didn't contain our File. We will have to open it ourselves,
// but before that, grab a write lock on handle in the VirtualFile, so
// that no other thread will try to concurrently open the same file.
let handle_guard = self.handle.write().await;
let handle_guard = self.handle.write().unwrap();

// If another thread changed the handle while we were not holding the lock,
// then the handle might now be valid again. Loop back to retry.
Expand All @@ -402,22 +390,25 @@ impl VirtualFile {

// We need to open the file ourselves. The handle in the VirtualFile is
// now locked in write-mode. Find a free slot to put it in.
let (handle, mut slot_guard) = open_files.find_victim_slot().await;
let (handle, mut slot_guard) = open_files.find_victim_slot();

// Open the physical file
let file = STORAGE_IO_TIME_METRIC
.get(StorageIoOperation::Open)
.observe_closure_duration(|| self.open_options.open(&self.path))?;

// Perform the requested operation on it
let result = STORAGE_IO_TIME_METRIC
.get(op)
.observe_closure_duration(|| func(&file));

// Store the File in the slot and update the handle in the VirtualFile
// to point to it.
slot_guard.file.replace(file);

*handle_guard = handle;

return Ok(FileGuard {
slot_guard: slot_guard.downgrade(),
});
Ok(result)
}

pub fn remove(self) {
Expand All @@ -432,9 +423,11 @@ impl VirtualFile {
self.pos = offset;
}
SeekFrom::End(offset) => {
self.pos = with_file!(self, StorageIoOperation::Seek, |file| file
.as_ref()
.seek(SeekFrom::End(offset)))?
self.pos = self
.with_file(StorageIoOperation::Seek, |mut file| {
file.seek(SeekFrom::End(offset))
})
.await??
}
SeekFrom::Current(offset) => {
let pos = self.pos as i128 + offset as i128;
Expand Down Expand Up @@ -522,9 +515,9 @@ impl VirtualFile {
}

pub async fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error> {
let result = with_file!(self, StorageIoOperation::Read, |file| file
.as_ref()
.read_at(buf, offset));
let result = self
.with_file(StorageIoOperation::Read, |file| file.read_at(buf, offset))
.await?;
if let Ok(size) = result {
STORAGE_IO_SIZE
.with_label_values(&["read", &self.tenant_id, &self.timeline_id])
Expand All @@ -534,9 +527,9 @@ impl VirtualFile {
}

async fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize, Error> {
let result = with_file!(self, StorageIoOperation::Write, |file| file
.as_ref()
.write_at(buf, offset));
let result = self
.with_file(StorageIoOperation::Write, |file| file.write_at(buf, offset))
.await?;
if let Ok(size) = result {
STORAGE_IO_SIZE
.with_label_values(&["write", &self.tenant_id, &self.timeline_id])
Expand All @@ -546,18 +539,6 @@ impl VirtualFile {
}
}

struct FileGuard<'a> {
slot_guard: RwLockReadGuard<'a, SlotInner>,
}

impl<'a> AsRef<File> for FileGuard<'a> {
fn as_ref(&self) -> &File {
// This unwrap is safe because we only create `FileGuard`s
// if we know that the file is Some.
self.slot_guard.file.as_ref().unwrap()
}
}

#[cfg(test)]
impl VirtualFile {
pub(crate) async fn read_blk(
Expand Down Expand Up @@ -590,39 +571,20 @@ impl VirtualFile {
impl Drop for VirtualFile {
/// If a VirtualFile is dropped, close the underlying file if it was open.
fn drop(&mut self) {
let handle = self.handle.get_mut();

fn clean_slot(slot: &Slot, mut slot_guard: RwLockWriteGuard<'_, SlotInner>, tag: u64) {
if slot_guard.tag == tag {
slot.recently_used.store(false, Ordering::Relaxed);
// there is also operation "close-by-replace" for closes done on eviction for
// comparison.
STORAGE_IO_TIME_METRIC
.get(StorageIoOperation::Close)
.observe_closure_duration(|| drop(slot_guard.file.take()));
}
}
let handle = self.handle.get_mut().unwrap();

// We don't have async drop so we cannot directly await the lock here.
// Instead, first do a best-effort attempt at closing the underlying
// file descriptor by using `try_write`, and if that fails, spawn
// a tokio task to do it asynchronously: we just want it to be
// cleaned up eventually.
// Most of the time, the `try_lock` should succeed though,
// as we have `&mut self` access. In other words, if the slot
// is still occupied by our file, there should be no access from
// other I/O operations; the only other possible place to lock
// the slot is the lock algorithm looking for free slots.
// We could check with a read-lock first, to avoid waiting on an
// unrelated I/O.
let slot = &get_open_files().slots[handle.index];
if let Ok(slot_guard) = slot.inner.try_write() {
clean_slot(slot, slot_guard, handle.tag);
} else {
let tag = handle.tag;
tokio::spawn(async move {
let slot_guard = slot.inner.write().await;
clean_slot(slot, slot_guard, tag);
});
};
let mut slot_guard = slot.inner.write().unwrap();
if slot_guard.tag == handle.tag {
slot.recently_used.store(false, Ordering::Relaxed);
// there is also operation "close-by-replace" for closes done on eviction for
// comparison.
STORAGE_IO_TIME_METRIC
.get(StorageIoOperation::Close)
.observe_closure_duration(|| drop(slot_guard.file.take()));
}
}
}

Expand Down

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