From 0985c73c9ab92575ecb6b297c48e38735dfba4d7 Mon Sep 17 00:00:00 2001
From: Nathan Daly <nathan.daly@relational.ai>
Date: Wed, 20 Sep 2023 01:13:44 -0600
Subject: [PATCH]  Export num_stack_mappings to track the number of in-flight
 stack mappings and tasks in application (#51301)

---
 src/gc-stacks.c | 4 ++++
 test/threads.jl | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/src/gc-stacks.c b/src/gc-stacks.c
index c04e48821e46f..693cb8d0eadf0 100644
--- a/src/gc-stacks.c
+++ b/src/gc-stacks.c
@@ -76,6 +76,10 @@ static void free_stack(void *stkbuf, size_t bufsz)
 }
 #endif
 
+JL_DLLEXPORT uint32_t jl_get_num_stack_mappings(void)
+{
+    return jl_atomic_load_relaxed(&num_stack_mappings);
+}
 
 const unsigned pool_sizes[] = {
     128 * 1024,
diff --git a/test/threads.jl b/test/threads.jl
index 8189311739e31..14fe94408a050 100644
--- a/test/threads.jl
+++ b/test/threads.jl
@@ -327,3 +327,9 @@ end
     @test_throws ArgumentError @macroexpand(@threads 1) # arg isn't an Expr
     @test_throws ArgumentError @macroexpand(@threads if true 1 end) # arg doesn't start with for
 end
+
+@testset "num_stack_mappings metric" begin
+    @test @ccall(jl_get_num_stack_mappings()::Cint) >= 1
+    # There must be at least two: one for the root test task and one for the async task:
+    @test fetch(@async(@ccall(jl_get_num_stack_mappings()::Cint))) >= 2
+end