From: Eric Wong Date: 2017-11-15T09:20:04+00:00 Subject: [ruby-core:83782] Re: [Ruby trunk Bug#14108] Seg Fault with MinGW on svn 60769 "U.NAKAMURA" wrote: > Hi, Eric, > > In message "[ruby-core:83779] Re: [Ruby trunk Bug#14108] Seg Fault with MinGW on svn 60769" > on Wed, 15 Nov 2017 07:12:42 +0000, normalperson@yhbt.net wrote: > > > You can see our implementation of readdir on Windows in > > > win32/win32.c (rb_w32_readdir). > > > I doubt the second argument (rb_encoding *enc) is the cause. > > As Nobu said at [ruby-core:83776] (thank you Nobu!), my guess was wrong > and the cause was touching GVL before running VM. > Therefore r60770 is the right way to resolve the problem. Right, that was a real bug, too. > > Right, enc is no problem. The problem is using DIR * from stdio > > is not reentrant or thread-safe. readdir_r is deprecated, even, > > and so it is up to the application to provide thread-safety when > > reading directories. > > Our readdir implementation for Win32 is expected to be thread-safe. > And, it seems that there is no platform which uses non thread-safe > readdir. OK, but do we know all platforms? Reading glibc, it seems readdir(3) is thread-safe (but not reentrant) at dirstream level (see below) > > Usually on modern platforms (but not guaranteed), readdir on > > different DIR * pointers is safe from multiple threads, so maybe > > we can add a mutex to "struct dir_data". > > > > I will revert r60772, r60770, and r60769 for now... > > So, IMO you don't need to revert them. > (but this mail is too late...) Linux readdir(3) man-page says: In the current POSIX.1 specification (POSIX.1-2008), readdir() is not required to be thread-safe. However, in modern implementations (including the glibc implementation), concurrent calls to readdir() that specify different directory streams are thread-safe. In cases where multiple threads must read from the same directory stream, using readdir() with external synchronization is still preferable to the use of the deprecated readdir_r(3) function. It is expected that a future version of POSIX.1 will require that readdir() be thread-safe when con��� currently employed on different directory streams. So based on that paragraph alone, my revert seems correct. Ruby Dir#read method can be called in multiple threads on the same Dir object. That is dangerous. However; when reading glibc source[1], I noticed every DIR stream has a lock which guards readdir calls since 1996[2]. So maybe whitelist glibc (and maybe win32) implementations for GVL release on readdir? [1] git://sourceware.org/git/glibc.git - sysdeps/posix/readdir.c [2] commit c150923988933b5db75a974d4cc08cd7f7aaf3dc in glibc[1] Unsubscribe: