Date: Sun, 8 Aug 2021 19:51:29 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 2a51e8823a60 - main - fork(2): comment about doubtful use of stdio and exit(3) in example Message-ID: <202108081951.178JpTuo030424@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=2a51e8823a60180feb534176bc41d5d10e2a01b1 commit 2a51e8823a60180feb534176bc41d5d10e2a01b1 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-08-05 16:03:03 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2021-08-08 19:38:59 +0000 fork(2): comment about doubtful use of stdio and exit(3) in example Add fflush(stdout) as the common idiom. Explain the need to use exit() but advise against it. Reviewed by: emaste, markj Sponsored by: The FreeBSD Foundation MFC after: 3 days Differential revision: https://reviews.freebsd.org/D31425 --- 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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