Add a semaphore to limit the number of threads downloading avatars

fractal-api/src/backend/mod.rs

@@ -1,6 +1,6 @@
 extern crate url;
 
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, Condvar};
 use std::thread;
 use self::url::Url;
 use std::sync::mpsc::{Sender, Receiver};
@@ -45,6 +45,7 @@ impl Backend {
             internal_tx: None,
             data: Arc::new(Mutex::new(data)),
             user_info_cache: CacheMap::new().timeout(60*60),
+            limit_threads: Arc::new((Mutex::new(0u8), Condvar::new())),
         }
     }
 

fractal-api/src/backend/types.rs

@@ -1,4 +1,4 @@
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, Condvar};
 use std::sync::mpsc::Sender;
 
 use error::Error;
@@ -133,6 +133,8 @@ pub struct Backend {
 
     // user info cache, uid -> (name, avatar)
     pub user_info_cache: CacheMap<Arc<Mutex<(String, String)>>>,
+    // semaphore to limit the number of threads downloading images
+    pub limit_threads: Arc<(Mutex<u8>, Condvar)>,
 }
 
 impl Clone for Backend {
@@ -142,6 +144,7 @@ impl Clone for Backend {
             data: self.data.clone(),
             internal_tx: self.internal_tx.clone(),
             user_info_cache: self.user_info_cache.clone(),
+            limit_threads: self.limit_threads.clone(),
         }
     }
 }

fractal-api/src/backend/user.rs

@@ -101,7 +101,21 @@ pub fn get_avatar_async(bk: &Backend, member: Option<Member>, tx: Sender<String>
     let alias = m.get_alias().clone();
     let avatar = m.avatar.clone();
 
+    let thread_count = bk.limit_threads.clone();
     thread::spawn(move || {
+        // waiting, less than 20 threads at the same time
+        // this is a semaphore
+        // TODO: use std::sync::Semaphore when it's on stable version
+        // https://doc.rust-lang.org/1.1.0/std/sync/struct.Semaphore.html
+        let &(ref num, ref cvar) = &*thread_count;
+        {
+            let mut start = num.lock().unwrap();
+            while *start >= 20 {
+                start = cvar.wait(start).unwrap()
+            }
+            *start += 1;
+        }
+
         match get_user_avatar_img(&baseu, uid, alias.unwrap_or_default(), avatar.unwrap_or_default()) {
             Ok(fname) => {
                 tx.send(fname.clone()).unwrap();
@@ -110,6 +124,13 @@ pub fn get_avatar_async(bk: &Backend, member: Option<Member>, tx: Sender<String>
                 tx.send(String::new()).unwrap();
             }
         }
+
+        // freeing the cvar for new threads
+        {
+            let mut counter = num.lock().unwrap();
+            *counter -= 1;
+        }
+        cvar.notify_one();
     });
 
     Ok(())

fractal-gtk/src/widgets/member.rs

@@ -36,7 +36,7 @@ impl<'a> MemberBox<'a> {
         username.set_text(&self.member.get_alias().unwrap_or_default());
 
         let avatar = gtk::Image::new_from_icon_name("avatar-default-symbolic", 3);
-        get_member_avatar(backend.clone(), avatar.clone(), Some(self.member.clone()), 30);
+        get_member_avatar(backend.clone(), avatar.clone(), Some(self.member.clone()), 30, 3);
         avatar.set_alignment(0.5, 0.);
 
         w.pack_start(&avatar, false, false, 5);
@@ -48,7 +48,11 @@ impl<'a> MemberBox<'a> {
     }
 }
 
-pub fn get_member_avatar(backend: Sender<BKCommand>, img: gtk::Image, m: Option<Member>, size: i32) {
+pub fn get_member_avatar(backend: Sender<BKCommand>, img: gtk::Image, m: Option<Member>, size: i32, tries: i32) {
+    if tries <= 0 {
+        return;
+    }
+
     let (tx, rx): (Sender<String>, Receiver<String>) = channel();
     backend.send(BKCommand::GetAvatarAsync(m.clone(), tx)).unwrap();
     gtk::timeout_add(50, move || match rx.try_recv() {
@@ -59,7 +63,7 @@ pub fn get_member_avatar(backend: Sender<BKCommand>, img: gtk::Image, m: Option<
             } else {
                 // trying again if fail
                 img.set_from_icon_name("avatar-default-symbolic", 5);
-                get_member_avatar(backend.clone(), img.clone(), m.clone(), size);
+                get_member_avatar(backend.clone(), img.clone(), m.clone(), size, tries - 1);
             }
 
             gtk::Continue(false)

fractal-gtk/src/widgets/message.rs

@@ -127,7 +127,7 @@ impl<'a> MessageBox<'a> {
             avatar = gtk::Image::new_from_icon_name("avatar-default-symbolic", 5);
         }
 
-        get_member_avatar(backend.clone(), avatar.clone(), m.cloned(), 40);
+        get_member_avatar(backend.clone(), avatar.clone(), m.cloned(), 40, 3);
         avatar.set_alignment(0.5, 0.);
 
         avatar