Refactor ReadPosition::is_past

fortanix · Oct 12, 2023 · 5703f54 · 5703f54
1 parent 9376cef
commit 5703f54
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Showing 3 changed files with 35 additions and 28 deletions.
diff --git a/intel-sgx/enclave-runner/src/usercalls/mod.rs b/intel-sgx/enclave-runner/src/usercalls/mod.rs
@@ -983,7 +983,13 @@ impl EnclaveState {
                     }
                     // cleanup old cancels
                     let read_position = usercall_queue_monitor.read_position();
-                    cancels.retain(|_id, wp| !read_position.is_past(wp));
+                    cancels.retain(|_id, wp|
+                        if let Some(past) = read_position.is_past(wp) {
+                            !past
+                        } else {
+                            false
+                        }
+                    );
                 }
             });
 

diff --git a/ipc-queue/src/interface_async.rs b/ipc-queue/src/interface_async.rs
@@ -193,28 +193,28 @@ mod tests {
         tx.send(Identified { id: id + 2, data: TestValue(3) }).await.unwrap();
         let p3 = monitor.write_position();
         id += 3;
-        assert!(monitor.read_position().is_past(&p0) == false);
-        assert!(monitor.read_position().is_past(&p1) == false);
-        assert!(monitor.read_position().is_past(&p2) == false);
-        assert!(monitor.read_position().is_past(&p3) == false);
+        assert!(monitor.read_position().is_past(&p0) == Some(false));
+        assert!(monitor.read_position().is_past(&p1) == Some(false));
+        assert!(monitor.read_position().is_past(&p2) == Some(false));
+        assert!(monitor.read_position().is_past(&p3) == Some(false));
 
         rx.recv().await.unwrap();
-        assert!(monitor.read_position().is_past(&p0) == true);
-        assert!(monitor.read_position().is_past(&p1) == false);
-        assert!(monitor.read_position().is_past(&p2) == false);
-        assert!(monitor.read_position().is_past(&p3) == false);
+        assert!(monitor.read_position().is_past(&p0) == Some(true));
+        assert!(monitor.read_position().is_past(&p1) == Some(false));
+        assert!(monitor.read_position().is_past(&p2) == Some(false));
+        assert!(monitor.read_position().is_past(&p3) == Some(false));
 
         rx.recv().await.unwrap();
-        assert!(monitor.read_position().is_past(&p0) == true);
-        assert!(monitor.read_position().is_past(&p1) == true);
-        assert!(monitor.read_position().is_past(&p2) == false);
-        assert!(monitor.read_position().is_past(&p3) == false);
+        assert!(monitor.read_position().is_past(&p0) == Some(true));
+        assert!(monitor.read_position().is_past(&p1) == Some(true));
+        assert!(monitor.read_position().is_past(&p2) == Some(false));
+        assert!(monitor.read_position().is_past(&p3) == Some(false));
 
         rx.recv().await.unwrap();
-        assert!(monitor.read_position().is_past(&p0) == true);
-        assert!(monitor.read_position().is_past(&p1) == true);
-        assert!(monitor.read_position().is_past(&p2) == true);
-        assert!(monitor.read_position().is_past(&p3) == false);
+        assert!(monitor.read_position().is_past(&p0) == Some(true));
+        assert!(monitor.read_position().is_past(&p1) == Some(true));
+        assert!(monitor.read_position().is_past(&p2) == Some(true));
+        assert!(monitor.read_position().is_past(&p3) == Some(false));
 
         for i in 0..1000 {
             let n = 1 + (i % LEN);
@@ -226,12 +226,12 @@ mod tests {
             let p5 = monitor.write_position();
             for _ in 0..n {
                 rx.recv().await.unwrap();
-                assert!(monitor.read_position().is_past(&p0) == true);
-                assert!(monitor.read_position().is_past(&p1) == true);
-                assert!(monitor.read_position().is_past(&p2) == true);
-                assert!(monitor.read_position().is_past(&p3) == true);
-                assert!(monitor.read_position().is_past(&p4) == true);
-                assert!(monitor.read_position().is_past(&p5) == false);
+                assert!(monitor.read_position().is_past(&p0) == Some(true));
+                assert!(monitor.read_position().is_past(&p1) == Some(true));
+                assert!(monitor.read_position().is_past(&p2) == Some(true));
+                assert!(monitor.read_position().is_past(&p3) == Some(true));
+                assert!(monitor.read_position().is_past(&p4) == Some(true));
+                assert!(monitor.read_position().is_past(&p5) == Some(false));
             }
         }
     }

diff --git a/ipc-queue/src/position.rs b/ipc-queue/src/position.rs
@@ -78,17 +78,18 @@ impl ReadPosition {
     /// A `WritePosition` can be compared to a `ReadPosition` **correctly** if
     /// the ring buffer wrapped around at most 2³¹ (2 to the power of 31) times.
     ///
-    /// Returns true if the read position and the write position differ by non-significant bit,
-    /// or if the read position is higher than the write position.
-    pub fn is_past(&self, write: &WritePosition) -> bool {
+    /// Returns `None` if the read position and the write position cannot be compared,
+    /// `Some(true)` if the read position is strictly higher than the write position,
+    /// `Some(false)` otherwise
+    pub fn is_past(&self, write: &WritePosition) -> Option<bool> {
         let (read, write) = (self.0, write.0);
 
         let hr = read & (1 << 63);
         let hw = write & (1 << 63);
         if hr == hw {
-            read > write
+            Some(read > write)
         } else {
-            true
+            None
         }
     }
 }