[RFC][PATCH v2 1/2][PR gdb/24069] [delete] Not-so-harmless spurious call to `wait4`

[Philippe Blain]

From: Dominique Quatravaux <dominique.quatravaux@epfl.ch>

As seen in https://sourceware.org/bugzilla/show_bug.cgi?id=24069 this
code will typically wait4() a second time on the same process that was
already wait4()'d a few lines above. While this used to be
harmless/idempotent (when we assumed that the process already exited),
this now causes a deadlock in the WIFSTOPPED case.

The early (~2019) history of bug #24069 cautiously suggests to use
WNOHANG instead of outright deleting the call. However, tests on the
current version of Darwin (Big Sur) demonstrate that gdb runs just
fine without a redundant call to wait4(), as would be expected.
Notwithstanding the debatable value of conserving bug compatibility
with an OS release that is more than a decade old, there is scant
evidence of what that double-wait4() was supposed to achieve in the
first place - A cursory investigation with `git blame` pinpoints
commits bb00b29d7802 and a80b95ba67e2 from the 2008-2009 era, but
fails to answer the “why” question conclusively.

ChangeLog:

2022-02-05  Dominique Quatravaux <dominique.quatravaux@epfl.ch>

        PR gdb/24609
        * gdb/darwin-nat.c (darwin_nat_target::decode_message): Remove
	spurious call to wait4.
---
 gdb/darwin-nat.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
index d96ce1a6c65..8b0ecfd5b77 100644
--- a/gdb/darwin-nat.c
+++ b/gdb/darwin-nat.c
@@ -1113,9 +1113,6 @@ darwin_nat_target::decode_message (mach_msg_header_t *hdr,
 	      inferior_debug (4, _("darwin_wait: pid=%d exit, status=0x%x\n"),
 			      res_pid, wstatus);
 
-	      /* Looks necessary on Leopard and harmless...  */
-	      wait4 (inf->pid, &wstatus, 0, NULL);
-
 	      return ptid_t (inf->pid);
 	    }
 	  else
-- 
2.29.2