From f417db52e0db2c930d646b8bfee0b2a1addc193e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arpad=20M=C3=BCller?= <arpad@neon.tech>
Date: Thu, 7 Sep 2023 15:48:30 +0200
Subject: [PATCH] wip

---
 pageserver/src/virtual_file.rs | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/pageserver/src/virtual_file.rs b/pageserver/src/virtual_file.rs
index 452f384f7c..f437deece7 100644
--- a/pageserver/src/virtual_file.rs
+++ b/pageserver/src/virtual_file.rs
@@ -12,6 +12,7 @@
 //!
 use crate::metrics::{STORAGE_IO_SIZE, STORAGE_IO_TIME};
 use crate::tenant::TENANTS_SEGMENT_NAME;
+use futures::Future;
 use once_cell::sync::OnceCell;
 use std::fs::{self, File, OpenOptions};
 use std::io::{Error, ErrorKind, Seek, SeekFrom};
@@ -330,19 +331,22 @@ impl VirtualFile {
 
     /// Call File::sync_all() on the underlying File.
     pub async fn sync_all(&self) -> Result<(), Error> {
-        self.with_file("fsync", |file| file.sync_all()).await?
+        self.with_file("fsync", |file| async move { file.sync_all() })
+            .await?
     }
 
     pub async fn metadata(&self) -> Result<fs::Metadata, Error> {
-        self.with_file("metadata", |file| file.metadata()).await?
+        self.with_file("metadata", |file| async move { file.metadata() })
+            .await?
     }
 
     /// 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: &str, mut func: F) -> Result<R, Error>
+    async fn with_file<'a, F, R, FR>(&self, _op: &str, func: F) -> Result<R, Error>
     where
-        F: FnMut(&File) -> R,
+        F: FnOnce(&'a File) -> FR,
+        FR: Future<Output = R> + 'a,
     {
         let open_files = get_open_files();
 
@@ -363,9 +367,7 @@ impl VirtualFile {
                         if let Some(file) = &slot_guard.file {
                             // Found a cached file descriptor.
                             slot.recently_used.store(true, Ordering::Relaxed);
-                            return Ok(STORAGE_IO_TIME
-                                .with_label_values(&[op])
-                                .observe_closure_duration(|| func(file)));
+                            return Ok(func(file).await);
                         }
                     }
                 }
@@ -395,9 +397,7 @@ impl VirtualFile {
             .observe_closure_duration(|| self.open_options.open(&self.path))?;
 
         // Perform the requested operation on it
-        let result = STORAGE_IO_TIME
-            .with_label_values(&[op])
-            .observe_closure_duration(|| func(&file));
+        let result = func(&file).await;
 
         // Store the File in the slot and update the handle in the VirtualFile
         // to point to it.
@@ -421,7 +421,9 @@ impl VirtualFile {
             }
             SeekFrom::End(offset) => {
                 self.pos = self
-                    .with_file("seek", |mut file| file.seek(SeekFrom::End(offset)))
+                    .with_file("seek", |mut file| async move {
+                        file.seek(SeekFrom::End(offset))
+                    })
                     .await??
             }
             SeekFrom::Current(offset) => {
@@ -511,7 +513,7 @@ impl VirtualFile {
 
     pub async fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error> {
         let result = self
-            .with_file("read", |file| file.read_at(buf, offset))
+            .with_file("read", |file| async move { file.read_at(buf, offset) })
             .await?;
         if let Ok(size) = result {
             STORAGE_IO_SIZE
@@ -523,7 +525,7 @@ impl VirtualFile {
 
     async fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize, Error> {
         let result = self
-            .with_file("write", |file| file.write_at(buf, offset))
+            .with_file("write", |file| async move { file.write_at(buf, offset) })
             .await?;
         if let Ok(size) = result {
             STORAGE_IO_SIZE