From c751f42f5f6a5e54a399df472015ab6d2ffc3f7a Mon Sep 17 00:00:00 2001 From: Eric Wong Date: Sun, 30 Dec 2012 11:43:10 +0000 Subject: accept: do not set blocking if non-blocking is set This is prone to race conditions in multiprocess situations where one process is relying on non-blocking operation while another (likely newer process) relies on blocking operation. Since the blocking process can always fall back to calling rb_io_wait_readable(), use that instead and give up some scalability for higher reliability. Those interested in avoiding thundering herds will have to stop/start their processes using blocking sockets (and tolerate some downtime). --- ext/kgio/accept.c | 36 +++--------------------------------- 1 file changed, 3 insertions(+), 33 deletions(-) diff --git a/ext/kgio/accept.c b/ext/kgio/accept.c index f8a073f..5f07532 100644 --- a/ext/kgio/accept.c +++ b/ext/kgio/accept.c @@ -79,15 +79,6 @@ static VALUE xaccept(void *ptr) #ifdef HAVE_RB_THREAD_BLOCKING_REGION # include # include "blocking_io_region.h" -/* - * Try to use a (real) blocking accept() since that can prevent - * thundering herds under Linux: - * http://www.citi.umich.edu/projects/linux-scalability/reports/accept.html - * - * So we periodically disable non-blocking, but not too frequently - * because other processes may set non-blocking (especially during - * a process upgrade) with Rainbows! concurrency model changes. - */ static int thread_accept(struct accept_args *a, int force_nonblock) { if (force_nonblock) @@ -95,28 +86,6 @@ static int thread_accept(struct accept_args *a, int force_nonblock) return (int)rb_thread_io_blocking_region(xaccept, a, a->fd); } -static void set_blocking_or_block(int fd) -{ - static time_t last_set_blocking; - time_t now = time(NULL); - - if (last_set_blocking == 0) { - last_set_blocking = now; - (void)rb_io_wait_readable(fd); - } else if ((now - last_set_blocking) <= 5) { - (void)rb_io_wait_readable(fd); - } else { - int flags = fcntl(fd, F_GETFL); - if (flags == -1) - rb_sys_fail("fcntl(F_GETFL)"); - if (flags & O_NONBLOCK) { - flags = fcntl(fd, F_SETFL, flags & ~O_NONBLOCK); - if (flags == -1) - rb_sys_fail("fcntl(F_SETFL)"); - } - last_set_blocking = now; - } -} #else /* ! HAVE_RB_THREAD_BLOCKING_REGION */ # include static int thread_accept(struct accept_args *a, int force_nonblock) @@ -134,7 +103,6 @@ static int thread_accept(struct accept_args *a, int force_nonblock) TRAP_END; return rv; } -#define set_blocking_or_block(fd) (void)rb_io_wait_readable(fd) #endif /* ! HAVE_RB_THREAD_BLOCKING_REGION */ static void @@ -209,7 +177,8 @@ retry: return Qnil; a->fd = my_fileno(a->accept_io); errno = EAGAIN; - set_blocking_or_block(a->fd); + (void)rb_io_wait_readable(a->fd); + /* fall-through to EINTR case */ #ifdef ECONNABORTED case ECONNABORTED: #endif /* ECONNABORTED */ @@ -217,6 +186,7 @@ retry: case EPROTO: #endif /* EPROTO */ case EINTR: + /* raise IOError if closed during sleep */ a->fd = my_fileno(a->accept_io); goto retry; case ENOMEM: -- cgit v1.2.3-24-ge0c7