fix: preserve the context state during evaluate — fixes #90, #93

src/main/java/com/dashjoin/jsonata/Jsonata.java

@@ -129,7 +129,17 @@ public void setEvaluateExitCallback(ExitCallback cb) {
     Object evaluate(Symbol expr, Object input, Frame environment) {
         // Thread safety:
         // Make sure each evaluate is executed on an instance per thread
-        return getPerThreadInstance()._evaluate(expr, input, environment);
+        Jsonata _this = getPerThreadInstance();
+        // Save and restore the evaluation context so that nested
+        // evaluations (e.g. $eval()) see the correct context.        
+        Object _input = _this.input;
+        Frame _environment = _this.environment;
+        try {
+          return _this._evaluate(expr, input, environment);
+        } finally {
+            _this.input = _input;
+            _this.environment = _environment;
+        }
     }
 
     Object _evaluate(Symbol expr, Object input, Frame environment) {

src/test/java/com/dashjoin/jsonata/ThreadSafetyTest.java

@@ -0,0 +1,296 @@
+package com.dashjoin.jsonata;
+
+import static com.dashjoin.jsonata.Jsonata.jsonata;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.*;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Thread safety and instance isolation tests for the Jsonata ThreadLocal fix.
+ * Covers GitHub issues #90 and #93, plus high-throughput concurrent scenarios.
+ */
+public class ThreadSafetyTest {
+
+    @Test
+    public void testTwoInstancesSameThread_bindingsDontLeak() {
+        Jsonata exprA = jsonata("$test");
+        Jsonata.Frame env = exprA.createFrame();
+        env.bind("test", "value_from_A");
+
+        // Constructing exprB must NOT corrupt exprA's evaluation context
+        Jsonata exprB = jsonata("$test");
+
+        Object resultA = exprA.evaluate("", env);
+        Object resultB = exprB.evaluate("");
+
+        assertEquals("value_from_A", resultA, "exprA should see its own binding");
+        assertNull(resultB, "exprB should NOT see exprA's binding");
+    }
+
+    @Test
+    public void testTwoInstancesSameThread_differentExpressions() {
+        Jsonata exprA = jsonata("a");
+        Jsonata exprB = jsonata("b");
+
+        assertEquals(1, exprA.evaluate(Map.of("a", 1, "b", 99)));
+        assertEquals(2, exprB.evaluate(Map.of("a", 99, "b", 2)));
+        // Re-evaluate exprA to confirm it still works correctly
+        assertEquals(3, exprA.evaluate(Map.of("a", 3, "b", 99)));
+    }
+
+    @Test
+    public void testManyInstancesSameThread_interleaved() {
+        Jsonata add = jsonata("a + b");
+        Jsonata mul = jsonata("a * b");
+        Jsonata evalExpr = jsonata("$eval('a')");
+
+        for (int i = 1; i <= 500; i++) {
+            assertEquals(i + 1, add.evaluate(Map.of("a", i, "b", 1)),
+                    "add failed at iteration " + i);
+            assertEquals(i * 2, mul.evaluate(Map.of("a", i, "b", 2)),
+                    "mul failed at iteration " + i);
+            assertEquals(i, evalExpr.evaluate(Map.of("a", i)),
+                    "eval failed at iteration " + i);
+        }
+    }
+
+    @Test
+    public void testEvalDeepContext() {
+        // This is the exact reproduction from issue #90
+        Jsonata expr = jsonata("$eval($.funcs.func)");
+        Object input = Map.of(
+                "funcs", Map.of("func", "$.a + $.b"),
+                "a", 3,
+                "b", 4
+        );
+        assertEquals(7, expr.evaluate(input));
+    }
+
+    @Test
+    public void testEvalWithSimplePath() {
+        Jsonata expr = jsonata("$eval('a')");
+        assertEquals(42, expr.evaluate(Map.of("a", 42)));
+    }
+
+    @Test
+    public void testEvalWithNestedPath() {
+        Jsonata expr = jsonata("$eval('a.b.c')");
+        assertEquals(99, expr.evaluate(
+                Map.of("a", Map.of("b", Map.of("c", 99)))));
+    }
+
+    @Test
+    public void testNestedEval() {
+        Jsonata expr = jsonata("$eval(\"$eval('a')\")");
+        assertEquals(7, expr.evaluate(Map.of("a", 7)));
+    }
+
+    @Test
+    public void testEvalWithinPathStepUsesCurrentItemContext() {
+        Jsonata expr = jsonata("items.$eval('a')");
+        Object input = Map.of(
+                "items", List.of(
+                        Map.of("a", 1),
+                        Map.of("a", 2)
+                )
+        );
+        assertEquals(List.of(1, 2), expr.evaluate(input));
+    }
+
+    @Test
+    public void testEvalWithinFilterUsesCurrentItemContext() {
+        Jsonata expr = jsonata("items[$eval('a') = 2].a");
+        Object input = Map.of(
+                "items", List.of(
+                        Map.of("a", 1),
+                        Map.of("a", 2)
+                )
+        );
+        assertEquals(2, expr.evaluate(input));
+    }
+
+    @Test
+    public void testCachedInstanceConcurrentThreads() throws Exception {
+        int threads = 10;
+        int itersPerThread = 1000;
+        Jsonata expr = jsonata("a + b");
+
+        CountDownLatch startGate = new CountDownLatch(1);
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        AtomicInteger errorCount = new AtomicInteger(0);
+        List<Future<?>> futures = new ArrayList<>();
+
+        for (int t = 0; t < threads; t++) {
+            final int threadId = t;
+            futures.add(pool.submit(() -> {
+                try {
+                    startGate.await();
+                } catch (InterruptedException e) { return; }
+
+                for (int i = 0; i < itersPerThread; i++) {
+                    Object result = expr.evaluate(Map.of("a", threadId, "b", 1));
+                    if (!Integer.valueOf(threadId + 1).equals(result)) {
+                        errorCount.incrementAndGet();
+                    }
+                }
+            }));
+        }
+
+        startGate.countDown(); // release all threads simultaneously
+        for (Future<?> f : futures) f.get(30, TimeUnit.SECONDS);
+        pool.shutdown();
+
+        assertEquals(0, errorCount.get(),
+                "Concurrent evaluation of cached instance produced wrong results");
+    }
+
+    @Test
+    public void testHighThroughputWithEval() throws Exception {
+        int threads = 16;
+        int itersPerThread = 2000;
+        Jsonata expr = jsonata("$eval('a') + b");
+
+        CountDownLatch startGate = new CountDownLatch(1);
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        AtomicInteger errorCount = new AtomicInteger(0);
+        List<String> sampleErrors = Collections.synchronizedList(new ArrayList<>());
+        List<Future<?>> futures = new ArrayList<>();
+
+        for (int t = 0; t < threads; t++) {
+            final int threadId = t;
+            futures.add(pool.submit(() -> {
+                try {
+                    startGate.await();
+                } catch (InterruptedException e) { return; }
+
+                int expected = threadId * 10 + threadId; // threadId * 11
+                for (int i = 0; i < itersPerThread; i++) {
+                    try {
+                        Object result = expr.evaluate(Map.of("a", threadId * 10, "b", threadId));
+                        if (!Integer.valueOf(expected).equals(result)) {
+                            errorCount.incrementAndGet();
+                            if (sampleErrors.size() < 5) {
+                                sampleErrors.add("thread-" + threadId + " iter-" + i +
+                                        ": expected " + expected + " got " + result);
+                            }
+                        }
+                    } catch (Exception e) {
+                        errorCount.incrementAndGet();
+                        if (sampleErrors.size() < 5) {
+                            sampleErrors.add("thread-" + threadId + " iter-" + i +
+                                    ": " + e.getClass().getSimpleName() + ": " + e.getMessage());
+                        }
+                    }
+                }
+            }));
+        }
+
+        startGate.countDown();
+        for (Future<?> f : futures) f.get(60, TimeUnit.SECONDS);
+        pool.shutdown();
+
+        assertEquals(0, errorCount.get(),
+                "High-throughput eval errors: " + sampleErrors);
+    }
+
+    @Test
+    public void testCustomFunctionMultiThread() throws Exception {
+        int threads = 10;
+        int itersPerThread = 500;
+        Jsonata expr = jsonata("$double(a)");
+        expr.registerFunction("double", (Integer x) -> x * 2);
+
+        CountDownLatch startGate = new CountDownLatch(1);
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        AtomicInteger errorCount = new AtomicInteger(0);
+        List<Future<?>> futures = new ArrayList<>();
+
+        for (int t = 0; t < threads; t++) {
+            final int threadId = t + 1; // 1-based to avoid $double(0)
+            futures.add(pool.submit(() -> {
+                try {
+                    startGate.await();
+                } catch (InterruptedException e) { return; }
+
+                int expected = threadId * 2;
+                for (int i = 0; i < itersPerThread; i++) {
+                    Object result = expr.evaluate(Map.of("a", threadId));
+                    if (!Integer.valueOf(expected).equals(result)) {
+                        errorCount.incrementAndGet();
+                    }
+                }
+            }));
+        }
+
+        startGate.countDown();
+        for (Future<?> f : futures) f.get(30, TimeUnit.SECONDS);
+        pool.shutdown();
+
+        assertEquals(0, errorCount.get(),
+                "Custom function multi-thread evaluation produced wrong results");
+    }
+
+    @Test
+    public void testCachedInstanceWithBindingsMultiThread() throws Exception {
+        int threads = 8;
+        int itersPerThread = 1000;
+        Jsonata expr = jsonata("$myVar + a");
+
+        CountDownLatch startGate = new CountDownLatch(1);
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        AtomicInteger errorCount = new AtomicInteger(0);
+        List<Future<?>> futures = new ArrayList<>();
+
+        for (int t = 0; t < threads; t++) {
+            final int threadId = t;
+            Jsonata.Frame frame = expr.createFrame();
+            frame.bind("myVar", threadId * 100);
+
+            futures.add(pool.submit(() -> {
+                try {
+                    startGate.await();
+                } catch (InterruptedException e) { return; }
+
+                int expected = threadId * 100 + threadId;
+                for (int i = 0; i < itersPerThread; i++) {
+                    Object result = expr.evaluate(Map.of("a", threadId), frame);
+                    if (!Integer.valueOf(expected).equals(result)) {
+                        errorCount.incrementAndGet();
+                    }
+                }
+            }));
+        }
+
+        startGate.countDown();
+        for (Future<?> f : futures) f.get(30, TimeUnit.SECONDS);
+        pool.shutdown();
+
+        assertEquals(0, errorCount.get(),
+                "Cached instance with per-thread bindings produced wrong results");
+    }
+
+    @Test
+    public void testNowWithCachedInstance() throws Exception {
+        Jsonata expr = jsonata("$now()");
+        Object r1 = expr.evaluate(null);
+        Thread.sleep(1100); // $now() has second-level precision
+        Object r2 = expr.evaluate(null);
+        assertNotNull(r1);
+        assertNotNull(r2);
+        assertNotEquals(r1, r2, "$now() should return different values on different calls");
+    }
+
+    @Test
+    public void testMillisWithCachedInstance() throws Exception {
+        Jsonata expr = jsonata("$millis()");
+        long r1 = ((Number) expr.evaluate(null)).longValue();
+        Thread.sleep(10);
+        long r2 = ((Number) expr.evaluate(null)).longValue();
+        assertTrue(r2 > r1, "$millis() should advance across separate evaluations");
+    }
+
+}