Date: Thu, 12 Aug 2021 12:39:29 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 5d7b612949c1 - stable/13 - fork(2): comment about doubtful use of stdio and exit(3) in example Message-ID: <202108121239.17CCdTqm059020@gitrepo.freebsd.org>
next in thread | raw e-mail | index | archive | help
The branch stable/13 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=5d7b612949c1c7f8a284d69e6db48a6c65cd16d3 commit 5d7b612949c1c7f8a284d69e6db48a6c65cd16d3 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-08-05 16:03:03 +0000 Commit: Konstantin Belousov <kib@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;
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202108121239.17CCdTqm059020>