handle reentrancy during initialization

src/snmalloc/global/threadalloc.h

@@ -180,8 +180,15 @@ namespace snmalloc
 
     /**
      * Used to give correct signature to teardown required by atexit.
+     * If [[gnu::destructor]] is available, we use the attribute to register
+     * the finalisation statically. In VERY rare cases, dynamic registration
+     * can trigger deadlocks.
      */
-    static void pthread_cleanup_main_thread()
+#    if __has_attribute(destructor)
+    [[gnu::destructor]]
+#    endif
+    static void
+    pthread_cleanup_main_thread()
     {
       ThreadAlloc::teardown();
     }
@@ -198,7 +205,9 @@ namespace snmalloc
       // run at least once.  If the main thread exits with `pthread_exit` then
       // it will be called twice but this case is already handled because other
       // destructors can cause the per-thread allocator to be recreated.
+#    if !__has_attribute(destructor)
       atexit(&pthread_cleanup_main_thread);
+#    endif
     }
 
   public:

src/test/func/multi_atexit/multi_atexit.cc

@@ -0,0 +1,42 @@
+#ifndef __has_feature
+#  define __has_feature(x) 0
+#endif
+
+#if defined(__linux__) && !__has_feature(address_sanitizer) && \
+  !__has_feature(thread_sanitizer) && \
+  !__has_feature(undefined_behavior_sanitizer) && \
+  !defined(__SANITIZE_ADDRESS__) && !defined(__SANITIZE_THREAD__) && \
+  !defined(__SANITIZE_UNDEFINED__)
+#  define RUN_TEST
+#endif
+
+#ifdef RUN_TEST
+#  include <snmalloc/snmalloc.h>
+#  include <stdlib.h>
+
+void do_nothing() {}
+
+// We only selectively override these functions. Otherwise, malloc may be called
+// before atexit triggers the first initialization attempt.
+
+extern "C" void* calloc(size_t num, size_t size)
+{
+  return snmalloc::libc::calloc(num, size);
+}
+
+extern "C" void free(void* p)
+{
+  if (snmalloc::is_owned(p))
+    return snmalloc::libc::free(p);
+  // otherwise, just leak the memory
+}
+
+#endif
+
+int main()
+{
+#ifdef RUN_TEST
+  for (int i = 0; i < 8192; ++i)
+    atexit(do_nothing);
+#endif
+}