Linux: use array element var handle

Author: manuelbl

java-does-usb/src/main/java/net/codecrete/usb/linux/EPoll.java

@@ -50,8 +50,14 @@ private EPoll() {}
                     JAVA_INT_UNALIGNED.withName("events"),
                     DATA$LAYOUT.withName("data")).withName("epoll_event");
 
+    // varhandle to access the "fd" field in an epoll_event array
+    static final VarHandle EVENT_ARRAY_DATA_FD$VH = EVENT$LAYOUT.arrayElementVarHandle(
+            MemoryLayout.PathElement.groupElement("data"),
+            MemoryLayout.PathElement.groupElement("fd")
+    );
+
     // varhandle to access the "fd" field in an epoll_event struct
-    static final VarHandle EVENT_DATA_FD$VH = EVENT$LAYOUT.varHandle(
+    private static final VarHandle EVENT_DATA_FD$VH = EVENT$LAYOUT.varHandle(
             MemoryLayout.PathElement.groupElement("data"),
             MemoryLayout.PathElement.groupElement("fd")
     );

java-does-usb/src/main/java/net/codecrete/usb/linux/LinuxAsyncTask.java

@@ -98,8 +98,7 @@ private void asyncCompletionTask() {
 
                 // for all ready file descriptors, reap URBs
                 for (int i = 0; i < res; i++) {
-                    var event = events.asSlice(i * EPoll.EVENT$LAYOUT.byteSize(), EPoll.EVENT$LAYOUT);
-                    var fd = (int) EPoll.EVENT_DATA_FD$VH.get(event, 0L);
+                    var fd = (int) EPoll.EVENT_ARRAY_DATA_FD$VH.get(events, 0L, i);
                     reapURBs(fd, urbPointerHolder, errorState);
                 }
             }