From 9ffe88841c86fd0c9845eee95640b59eeb837730 Mon Sep 17 00:00:00 2001
From: Awni Hannun <awni@apple.com>
Date: Tue, 18 Mar 2025 17:23:31 -0700
Subject: [PATCH] interruptable eval

---
 mlx/transforms.cpp   | 15 +++++++++++++++
 mlx/transforms.h     |  5 +++++
 tests/eval_tests.cpp | 14 +++++++++++++-
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/mlx/transforms.cpp b/mlx/transforms.cpp
index f01082418..5949a40bb 100644
--- a/mlx/transforms.cpp
+++ b/mlx/transforms.cpp
@@ -35,6 +35,11 @@ class Synchronizer : public Primitive {
   DEFINE_PRINT(Synchronize);
 };
 
+std::atomic<bool>& interrupt_flag() {
+  static std::atomic<bool> interrupt_{false};
+  return interrupt_;
+}
+
 // Initialize the static tracing members from transforms_impl.h
 //
 // These are used to implement the in_tracing() function the returns true if we
@@ -249,6 +254,12 @@ array eval_impl(std::vector<array> outputs, bool async) {
     if (!arr.is_tracer()) {
       arr.detach();
     }
+
+    if (interrupt_flag()) {
+      interrupt_flag() = false;
+      synchronizer.attach_event(Event{stream});
+      break;
+    }
   }
 
   // Signal the event in its stream
@@ -263,6 +274,10 @@ array eval_impl(std::vector<array> outputs, bool async) {
   return synchronizer;
 }
 
+void interrupt_eval() {
+  interrupt_flag() = true;
+}
+
 void async_eval(std::vector<array> outputs) {
   if (outputs.empty()) {
     return;
diff --git a/mlx/transforms.h b/mlx/transforms.h
index 4afb21e23..89b37c720 100644
--- a/mlx/transforms.h
+++ b/mlx/transforms.h
@@ -22,6 +22,11 @@ void eval(Arrays&&... outputs) {
   eval(std::vector<array>{std::forward<Arrays>(outputs)...});
 }
 
+/**
+ * Interrupt an ongoing eval. Leaves the graph in a valid state.
+ */
+void interrupt_eval();
+
 /**
  *  Computes the output and vector-Jacobian product (VJP) of a function.
  *
diff --git a/tests/eval_tests.cpp b/tests/eval_tests.cpp
index ce4bc980f..cd1b5dcaa 100644
--- a/tests/eval_tests.cpp
+++ b/tests/eval_tests.cpp
@@ -1,5 +1,4 @@
 // Copyright © 2023 Apple Inc.
-
 #include "doctest/doctest.h"
 
 #include "mlx/mlx.h"
@@ -91,3 +90,16 @@ TEST_CASE("test eval graph retention when not tracing") {
   CHECK(!a.has_primitive());
   CHECK(a.is_available());
 }
+
+TEST_CASE("test interrupt eval") {
+  auto x = zeros({1024}, int32);
+  for (int i = 0; i < 1000; ++i) {
+    x = x + 1;
+  }
+  std::thread t([x]() { eval(x); });
+  interrupt_eval();
+  t.join();
+  // Check that x is not evaluated
+  CHECK(!x.is_available());
+  CHECK(array_equal(x, full({1024}, 1000, int32)).item<bool>());
+}