fix(stdune): fix TSAN warning in wait4_stubs (ocaml#10554)

Fixes ocaml#10553 Quoting @jmid, using a local variable without the runtime lock in place, is against the rules. For integer values, sometimes the rules are bent, but this is not a good idea. See ocaml/ocaml#12737. Signed-off-by: Etienne Millon <[email protected]>
anmonteiro · Nov 17, 2024 · 889ef63 · 889ef63
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diff --git a/doc/changes/10554.md b/doc/changes/10554.md
@@ -0,0 +1 @@
+- fix TSAN warning in wait4 stubs (#10554, fixes #10553, @emillon)
diff --git a/otherlibs/stdune/src/wait4_stubs.c b/otherlibs/stdune/src/wait4_stubs.c
@@ -52,15 +52,16 @@ value dune_wait4(value v_pid, value flags) {
   CAMLparam2(v_pid, flags);
   CAMLlocal2(times, res);
 
-  int pid, status, cv_flags;
+  int status, cv_flags;
   struct timeval tp;
   cv_flags = caml_convert_flag_list(flags, wait_flag_table);
+  pid_t pid = Int_val(v_pid);
 
   struct rusage ru;
 
   caml_enter_blocking_section();
   // returns the pid of the terminated process, or -1 on error
-  pid = wait4(Int_val(v_pid), &status, cv_flags, &ru);
+  pid = wait4(pid, &status, cv_flags, &ru);
   gettimeofday(&tp, NULL);
   caml_leave_blocking_section();
   if (pid == -1)