start java

Author: cirosantilli

README.adoc

@@ -20936,6 +20936,8 @@ Maybe some day someone will use this setup to study the performance of interpret
 
 ==== Python
 
+link:rootfs_overlay/lkmc/python[]
+
 Examples:
 
 * link:rootfs_overlay/lkmc/python/hello.py[]: hello world
@@ -21095,6 +21097,8 @@ pybind11 is amazingly easy to use. But it can also make your builds really slow:
 
 ==== Node.js
 
+link:rootfs_overlay/lkmc/nodejs[]
+
 Host installation shown at: https://askubuntu.com/questions/594656/how-to-install-the-latest-versions-of-nodejs-and-npm/971612#971612
 
 Build and install the interpreter in Buildroot with:
@@ -21161,6 +21165,8 @@ https://stackoverflow.com/questions/31642477/how-to-publish-a-npm-package-with-d
 
 ==== Java
 
+link:rootfs_overlay/lkmc/java[]
+
 No OpenJDK package as of 2018.08: https://stackoverflow.com/questions/28874150/buildroot-with-jamvm-2-0-for-java-8/59290927#59290927 partly because their build system is shit like the rest of the project's setup.
 
 Unmerged patch at: http://lists.busybox.net/pipermail/buildroot/2018-February/213282.html
@@ -25639,6 +25645,8 @@ TODO create a minimal working aarch64 example analogous to the x86 one at: https
 
 A general introduction to paging with x86 examples can be found at: https://cirosantilli.com/x86-paging[].
 
+Then, this article is amazing: https://www.starlab.io/blog/deep-dive-mmu-virtualization-with-xen-on-arm
+
 ARM paging is documented at <<armarm8-db>> Chapter D5 and is mostly called VMSAv8 in the ARMv8 manual (Virtual Memory System Architecture).
 
 Paging is enabled by the `SCTLR_EL1.M` bit.

java

@@ -0,0 +1 @@
+rootfs_overlay/lkmc/java

rootfs_overlay/lkmc/java/LinkedHashMapCheat.java

@@ -0,0 +1,59 @@
+/*
+# LinkedHashMap
+
+http://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashMap.html
+
+Hash map that is iterable in insertion order.
+
+Application LRU cache:
+
+- https://github.com/haoel/leetcode/pull/90/files
+- http://stackoverflow.com/questions/23772102/lru-cache-in-java-with-generics-and-o1-operations
+
+This is a sub-case of a binary heap: it is efficient
+when every item update makes it either the most recent, or oldest.
+For more general binary heap, the new item can go anywhere.
+
+# removeEldestEntry
+
+Example:
+https://github.com/cirosantilli/haoel-leetcode/commit/ff04930b2dc31f270854e40b560723577c7b49fd
+
+Only acts on `put`, `get` does not update values for us.
+*/
+
+import java.util.LinkedList;
+import java.util.LinkedHashMap;
+import java.util.Iterator;
+
+public class LinkedHashMapCheat {
+    public static void main(String[] args) {
+        LinkedList<Integer> output;
+        LinkedList<Integer> expected;
+        Iterator<Integer> it;
+
+        LinkedHashMap<Integer,Integer> m = new LinkedHashMap<>();
+        assert m.put(2, -2) == null;
+        assert m.put(1, -1) == null;
+        assert m.put(3, -3) == null;
+        output = new LinkedList<>();
+        expected = new LinkedList<>();
+        expected.add(2);
+        expected.add(1);
+        expected.add(3);
+        for (int i : m.keySet())
+            output.add(i);
+        assert output.equals(expected);
+
+        it = m.keySet().iterator();
+        it.next();
+        it.remove();
+        output = new LinkedList<>();
+        expected = new LinkedList<>();
+        expected.add(1);
+        expected.add(3);
+        for (int i : m.keySet())
+            output.add(i);
+        assert output.equals(expected);
+    }
+}

rootfs_overlay/lkmc/java/Makefile

@@ -0,0 +1,40 @@
+IN_EXT ?= .java
+OUT_EXT ?= .class
+RUN ?= Main
+TEST ?= test
+
+OUTS := $(addsuffix $(OUT_EXT), $(basename $(wildcard *$(IN_EXT))))
+
+-include Makefile_params
+
+.PHONY: all clean run
+
+all:
+	javac *.java
+
+clean:
+	rm -f *$(OUT_EXT)
+
+run: all
+	java -ea $(RUN)
+
+test: all
+	@\
+	if [ -x $(TEST) ]; then \
+	  ./$(TEST) '$(OUTS)' ;\
+	else\
+	  fail=false ;\
+	  for t in $(basename $(OUTS)); do\
+	    if ! java -ea "$$t"; then \
+	      fail=true ;\
+	      break ;\
+	    fi ;\
+	  done ;\
+	  if $$fail; then \
+	    echo "TEST FAILED: $$t" ;\
+	    exit 1 ;\
+	  else \
+	    echo 'ALL TESTS PASSED' ;\
+	    exit 0 ;\
+	  fi ;\
+	fi ;\