diff --git a/hphp/runtime/ext/simplelock/ext_simplelock.cpp b/hphp/runtime/ext/simplelock/ext_simplelock.cpp
index 49caad6568f70f..7cbaec8d2e4078 100644
--- a/hphp/runtime/ext/simplelock/ext_simplelock.cpp
+++ b/hphp/runtime/ext/simplelock/ext_simplelock.cpp
@@ -134,6 +134,11 @@ void HHVM_FUNCTION(unlock_mutex, const String& name) {
   unlock(l);
 }
 
+bool HHVM_FUNCTION(is_held, const String& name) {
+  auto const l = get_lock(name.toCppString());
+  return l->load(std::memory_order_relaxed) != UNLOCKED;
+}
+
 struct SimpleLockExtension final : Extension {
   SimpleLockExtension() : Extension("simplelock", "1.0", "sandbox_infra") {}
 
@@ -142,6 +147,7 @@ struct SimpleLockExtension final : Extension {
   void moduleRegisterNative() override {
     HHVM_NAMED_FE(HH\\SimpleLock\\lock, HHVM_FN(lock_mutex));
     HHVM_NAMED_FE(HH\\SimpleLock\\try_lock, HHVM_FN(try_lock_mutex));
+    HHVM_NAMED_FE(HH\\SimpleLock\\is_held, HHVM_FN(is_held));
     HHVM_NAMED_FE_STR(
       "HH\\SimpleLock\\unlock", HHVM_FN(unlock_mutex), nativeFuncs()
     );
diff --git a/hphp/runtime/ext/simplelock/ext_simplelock.php b/hphp/runtime/ext/simplelock/ext_simplelock.php
index c72b7348f1aa29..4e2f2e4c257915 100644
--- a/hphp/runtime/ext/simplelock/ext_simplelock.php
+++ b/hphp/runtime/ext/simplelock/ext_simplelock.php
@@ -37,6 +37,16 @@ function unlock(string $name): void;
 <<__Native>>
 function try_lock(string $name): bool;
 
+/*
+ * Checks if any thread (including the current request) is holding a lock with a
+ * unique name.
+ *
+ * @param string $name - the name of the lock
+ * @return bool - whether someone is holding the lock
+ */
+<<__Native>>
+function is_held(string $name): bool;
+
 /*
  * Acquired a cross-request mutual exclusion lock with a unique name and a
  * timeout.
diff --git a/hphp/test/slow/simplelock/isheld.php b/hphp/test/slow/simplelock/isheld.php
new file mode 100644
index 00000000000000..f4b007b9df7bcc
--- /dev/null
+++ b/hphp/test/slow/simplelock/isheld.php
@@ -0,0 +1,61 @@
+<?hh
+
+async function thread_func() {
+  echo "thread\n";
+
+  await HH\SimpleLock\lock('thread_lock1');
+  await HH\SimpleLock\lock('thread_lock2');
+  await HH\SimpleLock\lock('end_lock');
+
+  echo 'thread: '; var_dump(HH\SimpleLock\is_held('main_lock1'));
+  echo 'thread: '; var_dump(HH\SimpleLock\is_held('main_lock2'));
+  echo 'thread: '; var_dump(HH\SimpleLock\is_held('thread_lock1'));
+  echo 'thread: '; var_dump(HH\SimpleLock\is_held('thread_lock2'));
+
+  $_ = true;
+  $t = apc_inc('threads', 1, inout $_);
+
+  await HH\SimpleLock\lock('sync');
+  HH\SimpleLock\unlock('thread_lock2');
+}
+
+function thread_main() {
+  HH\Asio\join(thread_func());
+}
+
+<<__EntryPoint>>
+async function main() {
+  if (HH\execution_context() === "xbox") return;
+
+  await HH\SimpleLock\lock('main_lock1');
+  await HH\SimpleLock\lock('main_lock2');
+  await HH\SimpleLock\lock('sync');
+  apc_store('threads', 0);
+
+  $func = fb_call_user_func_async(
+    __FILE__,
+    'thread_main'
+  );
+
+  $_ = true;
+  while (apc_fetch('threads', inout $_) !== 1) usleep(10);
+
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('main_lock1'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('main_lock2'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('thread_lock1'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('thread_lock2'));
+
+  HH\SimpleLock\unlock('sync');
+  fb_end_user_func_async($func);
+
+  HH\SimpleLock\unlock('main_lock2');
+  await HH\SimpleLock\lock('end_lock');
+
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('main_lock1'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('main_lock2'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('thread_lock1'));
+  echo 'main: '; var_dump(HH\SimpleLock\is_held('thread_lock2'));
+
+  echo "Main done.\n";
+}
+
diff --git a/hphp/test/slow/simplelock/isheld.php.expect b/hphp/test/slow/simplelock/isheld.php.expect
new file mode 100644
index 00000000000000..1477831ca668fe
--- /dev/null
+++ b/hphp/test/slow/simplelock/isheld.php.expect
@@ -0,0 +1,14 @@
+thread
+thread: bool(true)
+thread: bool(true)
+thread: bool(true)
+thread: bool(true)
+main: bool(true)
+main: bool(true)
+main: bool(true)
+main: bool(true)
+main: bool(true)
+main: bool(false)
+main: bool(false)
+main: bool(false)
+Main done.
diff --git a/hphp/test/slow/simplelock/isheld.php.norepo b/hphp/test/slow/simplelock/isheld.php.norepo
new file mode 100644
index 00000000000000..e69de29bb2d1d6