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Diffstat (limited to 'man3/flockfile.3')
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diff --git a/man3/flockfile.3 b/man3/flockfile.3 new file mode 100644 index 000000000..91c503eef --- /dev/null +++ b/man3/flockfile.3 @@ -0,0 +1,88 @@ +.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>. +.\" +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" +.TH LOCKFILE 3 2001-10-18 "" "Linux Programmer's Manual" +.SH NAME +flockfile, ftrylockfile, funlockfile \- lock FILE for stdio +.SH SYNOPSIS +.nf +.B #include <stdio.h> +.sp +.BI "void flockfile(FILE *" filehandle ); +.br +.BI "int ftrylockfile(FILE *" filehandle ); +.br +.BI "void funlockfile(FILE *" filehandle ); +.fi +.SH DESCRIPTION +The stdio functions are thread-safe. This is achieved by assigning +to each FILE object a lockcount and (if the lockcount is nonzero) +an owning thread. +For each library call, these functions wait until the FILE object +is no longer locked by a different thread, then lock it, do the +requested I/O, and unlock the object again. +.LP +(Note: this locking has nothing to do with the file locking done +by functions like +.BR flock (2) +and +.BR lockf (3).) +.LP +All this is invisible to the C-programmer, but there may be two +reasons to wish for more detailed control. On the one hand, maybe +a series of I/O actions by one thread belongs together, and should +not be interrupted by the I/O of some other thread. +On the other hand, maybe the locking overhead should be avoided +for greater efficiency. +.LP +To this end, a thread can explicitly lock the FILE object, +then do its series of I/O actions, then unlock. This prevents +other threads from coming in between. If the reason for doing +this was to achieve greater efficiency, one does the I/O with +the non-locking versions of the stdio functions: with +\fIgetc_unlocked\fP() and \fIputc_unlocked\fP() instead of +\fIgetc\fP() and \fIputc\fP(). +.LP +The \fBflockfile()\fP function waits for *\fIfilehandle\fP to be +no longer locked by a different thread, then makes the +current thread owner of *\fIfilehandle\fP, and increments +the lockcount. +.LP +The \fBfunlockfile()\fP function decrements the lock count. +.LP +The \fBftrylockfile()\fP function is a non-blocking version +of \fBflockfile()\fP. It does nothing in case some other thread +owns *\fIfilehandle\fP, and it obtains ownership and increments +the lockcount otherwise. +.SH "RETURN VALUE" +The \fBftrylockfile()\fP function returns zero for success +(the lock was obtained), and nonzero for failure. +.SH ERRORS +None. +.SH AVAILABILITY +These functions are available when _POSIX_THREAD_SAFE_FUNCTIONS +is defined. They are in libc since libc 5.1.1 and in glibc +since glibc 2.0. +.SH "CONFORMING TO" +POSIX.1 +.SH "SEE ALSO" +.BR unlocked_stdio (3) |