only interrupt during an eval

mlx/transforms.cpp

@@ -2,6 +2,7 @@
 #include <algorithm>
 #include <deque>
 #include <future>
+#include <mutex>
 #include <numeric>
 #include <set>
 #include <sstream>
@@ -35,11 +36,42 @@ class Synchronizer : public Primitive {
   DEFINE_PRINT(Synchronize);
 };
 
-std::atomic<bool>& interrupt_flag() {
+class Interrupt {
-  static std::atomic<bool> interrupt_{false};
+ private:
+  static std::mutex mutex_;
+  static bool eval_running_;
+  static bool interrupt_;
+
+ public:
+  Interrupt() {
+    std::unique_lock lk(mutex_);
+    eval_running_ = true;
+  }
+
+  static bool interrupt() {
+    std::unique_lock lk(mutex_);
+    if (eval_running_) {
+      interrupt_ = true;
+      return true;
+    }
+    return false;
+  }
+
+  static bool interrupted() {
+    std::unique_lock lk(mutex_);
     return interrupt_;
   }
 
+  ~Interrupt() {
+    std::unique_lock lk(mutex_);
+    eval_running_ = false;
+    interrupt_ = false;
+  }
+};
+std::mutex Interrupt::mutex_{};
+bool Interrupt::eval_running_ = false;
+bool Interrupt::interrupt_ = false;
+
 // Initialize the static tracing members from transforms_impl.h
 //
 // These are used to implement the in_tracing() function the returns true if we
@@ -50,6 +82,8 @@ std::vector<char> detail::InTracing::trace_stack{};
 int detail::RetainGraph::tracing_counter{0};
 
 array eval_impl(std::vector<array> outputs, bool async) {
+  Interrupt interrupt;
+
   std::deque<array> tape;
 
   // Make an effort to choose a good output stream
@@ -255,8 +289,7 @@ array eval_impl(std::vector<array> outputs, bool async) {
       arr.detach();
     }
 
-    if (interrupt_flag()) {
+    if (Interrupt::interrupted()) {
-      interrupt_flag() = false;
       synchronizer.attach_event(Event{stream});
       break;
     }
@@ -274,8 +307,8 @@ array eval_impl(std::vector<array> outputs, bool async) {
   return synchronizer;
 }
 
-void interrupt_eval() {
+bool interrupt_eval() {
-  interrupt_flag() = true;
+  return Interrupt::interrupt();
 }
 
 void async_eval(std::vector<array> outputs) {

mlx/transforms.h

@@ -23,9 +23,12 @@ void eval(Arrays&&... outputs) {
 }
 
 /**
- * Interrupt an ongoing eval. Leaves the graph in a valid state.
+ * Interrupt an ongoing eval.
+ *
+ * Leaves the graph in a valid state. Returns true if an ongoing eval was
+ * interrupted and false otherwise.
  */
-void interrupt_eval();
+bool interrupt_eval();
 
 /**
  *  Computes the output and vector-Jacobian product (VJP) of a function.

tests/eval_tests.cpp

@@ -97,7 +97,8 @@ TEST_CASE("test interrupt eval") {
     x = x + 1;
   }
   std::thread t([x]() { eval(x); });
-  interrupt_eval();
+  while (!interrupt_eval()) {
+  }
   t.join();
   // Check that x is not evaluated
   CHECK(!x.is_available());