Add naive garbage collector to StagingBelt

src/util/belt.rs

@@ -42,6 +42,7 @@ struct Chunk {
     buffer: Buffer,
     size: BufferAddress,
     offset: BufferAddress,
+    tick: u64,
 }
 
 /// Staging belt is a machine that uploads data.
@@ -65,6 +66,7 @@ pub struct StagingBelt {
     free_chunks: Vec<Chunk>,
     sender: mpsc::Sender<Chunk>,
     receiver: mpsc::Receiver<Chunk>,
+    tick: u64,
 }
 
 impl StagingBelt {
@@ -82,6 +84,7 @@ impl StagingBelt {
             free_chunks: Vec::new(),
             sender,
             receiver,
+            tick: 0,
         }
     }
 
@@ -123,8 +126,10 @@ impl StagingBelt {
                 }),
                 size,
                 offset: 0,
+                tick: 0,
             }
         };
+        chunk.tick = self.tick;
 
         encoder.copy_buffer_to_buffer(&chunk.buffer, chunk.offset, target, offset, size.get());
         let old_offset = chunk.offset;
@@ -183,7 +188,16 @@ impl StagingBelt {
                 })
             })
             .collect::<Vec<_>>();
+        self.gc();
 
         Join { futures }
     }
+
+    fn gc(&mut self) {
+        self.tick += 1;
+        if (self.tick % 20) == 0 {
+            let t = self.tick;
+            self.free_chunks.retain(|chunk| {(t - chunk.tick) < 10});
+        }
+    }
 }