The branch stable/13 has been updated by kib:
URL:
https://cgit.FreeBSD.org/src/commit/?id=5d7b612949c1c7f8a284d69e6db48a6c65cd16d3
commit 5d7b612949c1c7f8a284d69e6db48a6c65cd16d3
Author: Konstantin Belousov <k...@freebsd.org>
AuthorDate: 2021-08-05 16:03:03 +0000
Commit: Konstantin Belousov <k...@freebsd.org>
CommitDate: 2021-08-12 12:37:54 +0000
fork(2): comment about doubtful use of stdio and exit(3) in example
(cherry picked from commit 2a51e8823a60180feb534176bc41d5d10e2a01b1)
---
lib/libc/sys/fork.2 | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/lib/libc/sys/fork.2 b/lib/libc/sys/fork.2
index d841b0bc38e1..dbde8f5275aa 100644
--- a/lib/libc/sys/fork.2
+++ b/lib/libc/sys/fork.2
@@ -28,7 +28,7 @@
.\" @(#)fork.2 8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
-.Dd August 2, 2021
+.Dd August 5, 2021
.Dt FORK 2
.Os
.Sh NAME
@@ -172,11 +172,28 @@ main(void)
{
pid_t pid;
+ /*
+ * If child is expected to use stdio(3), state of
+ * the reused io streams must be synchronized between
+ * parent and child, to avoid double output and other
+ * possible issues.
+ */
+ fflush(stdout);
+
switch (pid = fork()) {
case -1:
err(1, "Failed to fork");
case 0:
printf("Hello from child process!\en");
+
+ /*
+ * Since we wrote into stdout, child needs to use
+ * exit(3) and not _exit(2). This causes handlers
+ * registered with atexit(3) to be called twice,
+ * once in parent, and once in the child. If such
+ * behavior is undesirable, consider
+ * terminating child with _exit(2) or _Exit(3).
+ */
exit(0);
default:
break;
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