diff options
| -rw-r--r-- | ChangeLog | 6 | ||||
| -rw-r--r-- | manual/filesys.texi | 29 |
2 files changed, 26 insertions, 9 deletions
@@ -1,3 +1,9 @@ +2017-04-11 Florian Weimer <fweimer@redhat.com> + Zack Weinberg <zackw@panix.com> + + * manual/filesys.texi (Reading/Closing Directory): Mark readdir, + readdir64 as thread-safe. Update warning about readdir_r. + 2017-04-10 Adhemerval Zanella <adhemerval.zanella@linaro.org> * sysdeps/unix/sysv/linux/x86/Implies: New file. diff --git a/manual/filesys.texi b/manual/filesys.texi index edc7c64..a255c8f 100644 --- a/manual/filesys.texi +++ b/manual/filesys.texi @@ -478,7 +478,7 @@ symbols are declared in the header file @file{dirent.h}. @comment dirent.h @comment POSIX.1 @deftypefun {struct dirent *} readdir (DIR *@var{dirstream}) -@safety{@prelim{}@mtunsafe{@mtasurace{:dirstream}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}} +@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}} @c This function holds dirstream's non-recursive lock, which brings @c about the usual issues with locks and async signals and cancellation, @c but the lock taking is not enough to make the returned value safe to @@ -507,13 +507,24 @@ must set @code{errno} to zero before calling @code{readdir}. To avoid entering an infinite loop, you should stop reading from the directory after the first error. -In POSIX.1-2008, @code{readdir} is not thread-safe. In @theglibc{} -implementation, it is safe to call @code{readdir} concurrently on -different @var{dirstream}s, but multiple threads accessing the same -@var{dirstream} result in undefined behavior. @code{readdir_r} is a -fully thread-safe alternative, but suffers from poor portability (see -below). It is recommended that you use @code{readdir}, with external -locking if multiple threads access the same @var{dirstream}. +@strong{Caution:} The pointer returned by @code{readdir} points to +a buffer within the @code{DIR} object. The data in that buffer will +be overwritten by the next call to @code{readdir}. You must take care, +for instance, to copy the @code{d_name} string if you need it later. + +Because of this, it is not safe to share a @code{DIR} object among +multiple threads, unless you use your own locking to ensure that +no thread calls @code{readdir} while another thread is still using the +data from the previous call. In @theglibc{}, it is safe to call +@code{readdir} from multiple threads as long as each thread uses +its own @code{DIR} object. POSIX.1-2008 does not require this to +be safe, but we are not aware of any operating systems where it +does not work. + +@code{readdir_r} allows you to provide your own buffer for the +@code{struct dirent}, but it is less portable than @code{readdir}, and +has problems with very long filenames (see below). We recommend +you use @code{readdir}, but do not share @code{DIR} objects. @end deftypefun @comment dirent.h @@ -592,7 +603,7 @@ of the last two functions. @comment dirent.h @comment LFS @deftypefun {struct dirent64 *} readdir64 (DIR *@var{dirstream}) -@safety{@prelim{}@mtunsafe{@mtasurace{:dirstream}}@asunsafe{@asulock{}}@acunsafe{@aculock{}}} +@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}} The @code{readdir64} function is just like the @code{readdir} function except that it returns a pointer to a record of type @code{struct dirent64}. Some of the members of this data type (notably @code{d_ino}) |