Lock cfunction trampoline cache and freelist accesses. (#39621)

Co-authored-by: Valentin Churavy <v.churavy@gmail.com>

Author: maleadt

src/runtime_ccall.cpp

@@ -210,9 +210,11 @@ extern "C" JL_DLLEXPORT char *jl_format_filename(const char *output_pattern)
 }
 
 
+static jl_mutex_t trampoline_lock;          // for accesses to the cache and freelist
+
 static void *trampoline_freelist;
 
-static void *trampoline_alloc()
+static void *trampoline_alloc()             // lock taken by caller
 {
     const int sz = 64; // oversized for most platforms. todo: use precise value?
     if (!trampoline_freelist) {
@@ -245,7 +247,7 @@ static void *trampoline_alloc()
     return tramp;
 }
 
-static void trampoline_free(void *tramp)
+static void trampoline_free(void *tramp)    // lock taken by caller
 {
     *(void**)tramp = trampoline_freelist;
     trampoline_freelist = tramp;
@@ -260,17 +262,18 @@ static void trampoline_deleter(void **f)
     f[0] = NULL;
     f[2] = NULL;
     f[3] = NULL;
+    JL_LOCK_NOGC(&trampoline_lock);
     if (tramp)
         trampoline_free(tramp);
     if (fobj && cache)
         ptrhash_remove((htable_t*)cache, fobj);
     if (nval)
         free(nval);
+    JL_UNLOCK_NOGC(&trampoline_lock);
 }
 
 // Use of `cache` is not clobbered in JL_TRY
 JL_GCC_IGNORE_START("-Wclobbered")
-// TODO: need a thread lock around the cache access parts of this function
 extern "C" JL_DLLEXPORT
 jl_value_t *jl_get_cfunction_trampoline(
     // dynamic inputs:
@@ -284,6 +287,7 @@ jl_value_t *jl_get_cfunction_trampoline(
     jl_value_t **vals)
 {
     // lookup (fobj, vals) in cache
+    JL_LOCK_NOGC(&trampoline_lock);
     if (!cache->table)
         htable_new(cache, 1);
     if (fill != jl_emptysvec) {
@@ -295,6 +299,7 @@ jl_value_t *jl_get_cfunction_trampoline(
         }
     }
     void *tramp = ptrhash_get(cache, (void*)fobj);
+    JL_UNLOCK_NOGC(&trampoline_lock);
     if (tramp != HT_NOTFOUND) {
         assert((jl_datatype_t*)jl_typeof(tramp) == result_type);
         return (jl_value_t*)tramp;
@@ -347,10 +352,12 @@ jl_value_t *jl_get_cfunction_trampoline(
         free(nval);
         jl_rethrow();
     }
+    JL_LOCK_NOGC(&trampoline_lock);
     tramp = trampoline_alloc();
     ((void**)result)[0] = tramp;
     tramp = init_trampoline(tramp, nval);
     ptrhash_put(cache, (void*)fobj, result);
+    JL_UNLOCK_NOGC(&trampoline_lock);
     return result;
 }
 JL_GCC_IGNORE_STOP

test/threads_exec.jl

@@ -471,7 +471,6 @@ end
 
 function test_thread_cfunction()
     # ensure a runtime call to `get_trampoline` will be created
-    # TODO: get_trampoline is not thread-safe (as this test shows)
     fs = [ Core.Box() for i in 1:1000 ]
     @noinline cf(f) = @cfunction $f Float64 ()
     cfs = Vector{Base.CFunction}(undef, length(fs))
@@ -494,11 +493,7 @@ function test_thread_cfunction()
     @test sum(ok) == 10000
 end
 if cfunction_closure
-    if nthreads() == 1
-        test_thread_cfunction()
-    else
-        @test_broken "cfunction trampoline code not thread-safe"
-    end
+    test_thread_cfunction()
 end
 
 # Compare the two ways of checking if threading is enabled.