fix: restore try_many_times workaround

Even though r2d2 connection pool is removed,
deleting accounts still fails in Windows CI.

This reverts commit e88f21c010.
`try_many_times` documentation is modified to explain
why the workaround is still needed.

src/accounts.rs

@@ -1,6 +1,7 @@
 //! # Account manager module.
 
 use std::collections::BTreeMap;
+use std::future::Future;
 use std::path::{Path, PathBuf};
 
 use anyhow::{ensure, Context as _, Result};
@@ -155,7 +156,7 @@ impl Accounts {
         if let Some(cfg) = self.config.get_account(id) {
             let account_path = self.dir.join(cfg.dir);
 
-            fs::remove_dir_all(&account_path)
+            try_many_times(|| fs::remove_dir_all(&account_path))
                 .await
                 .context("failed to remove account data")?;
         }
@@ -191,10 +192,10 @@ impl Accounts {
             fs::create_dir_all(self.dir.join(&account_config.dir))
                 .await
                 .context("failed to create dir")?;
-            fs::rename(&dbfile, &new_dbfile)
+            try_many_times(|| fs::rename(&dbfile, &new_dbfile))
                 .await
                 .context("failed to rename dbfile")?;
-            fs::rename(&blobdir, &new_blobdir)
+            try_many_times(|| fs::rename(&blobdir, &new_blobdir))
                 .await
                 .context("failed to rename blobdir")?;
             if walfile.exists() {
@@ -219,7 +220,7 @@ impl Accounts {
             }
             Err(err) => {
                 let account_path = std::path::PathBuf::from(&account_config.dir);
-                fs::remove_dir_all(&account_path)
+                try_many_times(|| fs::remove_dir_all(&account_path))
                     .await
                     .context("failed to remove account data")?;
                 self.config.remove_account(account_config.id).await?;
@@ -560,6 +561,37 @@ impl Config {
     }
 }
 
+/// Spend up to 1 minute trying to do the operation.
+///
+/// Even if Delta Chat itself does not hold the file lock,
+/// there may be other processes such as antivirus,
+/// or the filesystem may be network-mounted.
+///
+/// Without this workaround removing account may fail on Windows with an error
+/// "The process cannot access the file because it is being used by another process. (os error 32)".
+async fn try_many_times<F, Fut, T>(f: F) -> std::result::Result<(), T>
+where
+    F: Fn() -> Fut,
+    Fut: Future<Output = std::result::Result<(), T>>,
+{
+    let mut counter = 0;
+    loop {
+        counter += 1;
+
+        if let Err(err) = f().await {
+            if counter > 60 {
+                return Err(err);
+            }
+
+            // Wait 1 second and try again.
+            tokio::time::sleep(std::time::Duration::from_millis(1000)).await;
+        } else {
+            break;
+        }
+    }
+    Ok(())
+}
+
 /// Configuration of a single account.
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 struct AccountConfig {