fix: do not lock the account manager for the whole duration of background_fetch

deltachat-ffi/src/lib.rs

@@ -4882,12 +4882,12 @@ pub unsafe extern "C" fn dc_accounts_background_fetch(
     }
 
     let accounts = &*accounts;
-    block_on(async move {
-        let accounts = accounts.read().await;
-        accounts
-            .background_fetch(Duration::from_secs(timeout_in_seconds))
-            .await;
-    });
+    let background_fetch_future = {
+        let lock = block_on(accounts.read());
+        lock.background_fetch(Duration::from_secs(timeout_in_seconds))
+    };
+    // At this point account manager is not locked anymore.
+    block_on(background_fetch_future);
     1
 }
 

deltachat-jsonrpc/src/api.rs

@@ -254,11 +254,12 @@ impl CommandApi {
     /// Process all events until you get this one and you can safely return to the background
     /// without forgetting to create notifications caused by timing race conditions.
     async fn accounts_background_fetch(&self, timeout_in_seconds: f64) -> Result<()> {
-        self.accounts
-            .write()
-            .await
-            .background_fetch(std::time::Duration::from_secs_f64(timeout_in_seconds))
-            .await;
+        let future = {
+            let lock = self.accounts.read().await;
+            lock.background_fetch(std::time::Duration::from_secs_f64(timeout_in_seconds))
+        };
+        // At this point account manager is not locked anymore.
+        future.await;
         Ok(())
     }
 

src/accounts.rs

@@ -5,7 +5,8 @@ use std::future::Future;
 use std::path::{Path, PathBuf};
 
 use anyhow::{ensure, Context as _, Result};
-use futures::future::join_all;
+use futures::stream::FuturesUnordered;
+use futures::StreamExt;
 use serde::{Deserialize, Serialize};
 use tokio::fs;
 use tokio::io::AsyncWriteExt;
@@ -301,20 +302,48 @@ impl Accounts {
     ///
     /// This is an auxiliary function and not part of public API.
     /// Use [Accounts::background_fetch] instead.
-    async fn background_fetch_without_timeout(&self) {
+    async fn background_fetch_no_timeout(accounts: Vec<Context>, events: Events) {
         async fn background_fetch_and_log_error(account: Context) {
             if let Err(error) = account.background_fetch().await {
                 warn!(account, "{error:#}");
             }
         }
 
-        join_all(
-            self.accounts
-                .values()
-                .cloned()
-                .map(background_fetch_and_log_error),
+        events.emit(Event {
+            id: 0,
+            typ: EventType::Info(format!(
+                "Starting background fetch for {} accounts.",
+                accounts.len()
+            )),
+        });
+        let mut futures_unordered: FuturesUnordered<_> = accounts
+            .into_iter()
+            .map(background_fetch_and_log_error)
+            .collect();
+        while futures_unordered.next().await.is_some() {}
+    }
+
+    /// Auxiliary function for [Accounts::background_fetch].
+    async fn background_fetch_with_timeout(
+        accounts: Vec<Context>,
+        events: Events,
+        timeout: std::time::Duration,
+    ) {
+        if let Err(_err) = tokio::time::timeout(
+            timeout,
+            Self::background_fetch_no_timeout(accounts, events.clone()),
         )
-        .await;
+        .await
+        {
+            events.emit(Event {
+                id: 0,
+                typ: EventType::Warning("Background fetch timed out.".to_string()),
+            });
+        }
+        events.emit(Event {
+            id: 0,
+            typ: EventType::AccountsBackgroundFetchDone,
+        });
     }
 
     /// Performs a background fetch for all accounts in parallel with a timeout.
@@ -322,15 +351,13 @@ impl Accounts {
     /// The `AccountsBackgroundFetchDone` event is emitted at the end,
     /// process all events until you get this one and you can safely return to the background
     /// without forgetting to create notifications caused by timing race conditions.
-    pub async fn background_fetch(&self, timeout: std::time::Duration) {
-        if let Err(_err) =
-            tokio::time::timeout(timeout, self.background_fetch_without_timeout()).await
-        {
-            self.emit_event(EventType::Warning(
-                "Background fetch timed out.".to_string(),
-            ));
-        }
-        self.emit_event(EventType::AccountsBackgroundFetchDone);
+    ///
+    /// Returns a future that resolves when background fetch is done,
+    /// but does not capture `&self`.
+    pub fn background_fetch(&self, timeout: std::time::Duration) -> impl Future<Output = ()> {
+        let accounts: Vec<Context> = self.accounts.values().cloned().collect();
+        let events = self.events.clone();
+        Self::background_fetch_with_timeout(accounts, events, timeout)
     }
 
     /// Emits a single event.