From a7344320998fab8822c9f89744bf6a102e478d09 Mon Sep 17 00:00:00 2001 From: Eric Wong Date: Sun, 20 Oct 2013 04:03:40 +0000 Subject: [PATCH] io.c: make IO#reopen("pathname") atomic Since rb_sysopen releases the GVL, calling close(fptr->fd) would leave a window where accessing the file from another thread can hit IOError on a closed stream Instead, create a new, temporary FD via rb_sysopen and call rb_cloexec_dup2 on it to atomically replace the file fptr->fd points to. This leaves no possible window where fptr->fd is invalid to userspace (even for any threads running w/o GVL). Without this patch, I need to maintain separate code paths for atomically reopening (e.g. log rotation) std{in,out,err} vs other files in a multithreaded application. --- io.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/io.c b/io.c index 47b86ed..66e19aa 100644 --- a/io.c +++ b/io.c @@ -6665,10 +6665,16 @@ rb_io_reopen(int argc, VALUE *argv, VALUE file) } } else { - if (close(fptr->fd) < 0) + int tmpfd = rb_sysopen(fptr->pathv, oflags, 0666); + int err = 0; + + if (rb_cloexec_dup2(tmpfd, fptr->fd) < 0) + err = errno; + (void)close(tmpfd); + if (err) { + errno = err; rb_sys_fail_path(fptr->pathv); - fptr->fd = -1; - fptr->fd = rb_sysopen(fptr->pathv, oflags, 0666); + } } return file; -- 1.8.4.483.g7fe67e6.dirty