details: http://hg.nginx.org/nginx/rev/f7849bfb6d21
branches:
changeset: 6536:f7849bfb6d21
user: Valentin Bartenev <vbart@nginx.com>
date: Fri May 13 17:19:23 2016 +0300
description:
Improved EPOLLRDHUP handling.

When it's known that the kernel supports EPOLLRDHUP, there is no need in
additional recv() call to get EOF or error when the flag is absent in the
event generated by the kernel. A special runtime test is done at startup
to detect if EPOLLRDHUP is actually supported by the kernel because
epoll_ctl() silently ignores unknown flags.

With this knowledge it's now possible to drop the "ready" flag for partial
read. Previously, the "ready" flag was kept until the recv() returned EOF
or error. In particular, this change allows the lingering close heuristics
(which relies on the "ready" flag state) to actually work on Linux, and not
wait for more data in most cases.

The "available" flag is now used in the read event with the semantics similar
to the corresponding counter in kqueue.

diffstat:

src/event/modules/ngx_epoll_module.c | 72 +++++++++++++++++++++++++++++++++++-
src/event/ngx_event.h | 7 +++
src/http/ngx_http_request.c | 6 ++-
src/http/ngx_http_upstream.c | 6 ++-
src/os/unix/ngx_readv_chain.c | 32 ++++++++++++++++
src/os/unix/ngx_recv.c | 33 ++++++++++++++++
6 files changed, 153 insertions(+), 3 deletions(-)

diffs (269 lines):

diff -r db699978a33f -r f7849bfb6d21 src/event/modules/ngx_epoll_module.c
--- a/src/event/modules/ngx_epoll_module.c Thu May 12 16:43:19 2016 +0300
+++ b/src/event/modules/ngx_epoll_module.c Fri May 13 17:19:23 2016 +0300
@@ -123,6 +123,7 @@ static ngx_int_t ngx_epoll_process_event
static void ngx_epoll_eventfd_handler(ngx_event_t *ev);
#endif

+static ngx_int_t ngx_epoll_module_init(ngx_cycle_t *cycle);
static void *ngx_epoll_create_conf(ngx_cycle_t *cycle);
static char *ngx_epoll_init_conf(ngx_cycle_t *cycle, void *conf);

@@ -146,6 +147,10 @@ static ngx_connection_t ngx_eventfd_

#endif

+#if (NGX_HAVE_EPOLLRDHUP)
+ngx_uint_t ngx_use_epoll_rdhup;
+#endif
+
static ngx_str_t epoll_name = ngx_string("epoll");

static ngx_command_t ngx_epoll_commands[] = {
@@ -197,7 +202,7 @@ ngx_module_t ngx_epoll_module = {
ngx_epoll_commands, /* module directives */
NGX_EVENT_MODULE, /* module type */
NULL, /* init master */
- NULL, /* init module */
+ ngx_epoll_module_init, /* init module */
NULL, /* init process */
NULL, /* init thread */
NULL, /* exit thread */
@@ -808,6 +813,8 @@ ngx_epoll_process_events(ngx_cycle_t *cy
if (revents & EPOLLRDHUP) {
rev->pending_eof = 1;
}
+
+ rev->available = 1;
#endif

rev->ready = 1;
@@ -943,6 +950,69 @@ ngx_epoll_eventfd_handler(ngx_event_t *e
#endif


+static ngx_int_t
+ngx_epoll_module_init(ngx_cycle_t *cycle)
+{
+#if (NGX_HAVE_EPOLLRDHUP)
+ int epfd, s[2], events;
+ struct epoll_event ee;
+
+ epfd = epoll_create(1);
+
+ if (epfd == -1) {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "epoll_create() failed");
+ return NGX_ERROR;
+ }
+
+ if (socketpair(AF_UNIX, SOCK_STREAM, 0, s) == -1) {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "socketpair() failed");
+ return NGX_ERROR;
+ }
+
+ ee.events = EPOLLET|EPOLLIN|EPOLLRDHUP;
+
+ if (epoll_ctl(epfd, EPOLL_CTL_ADD, s[0], &ee) == -1) {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "epoll_ctl() failed");
+ return NGX_ERROR;
+ }
+
+ if (close(s[1]) == -1) {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "close() failed");
+ return NGX_ERROR;
+ }
+
+ events = epoll_wait(epfd, &ee, 1, 5000);
+
+ if (events == -1) {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "epoll_wait() failed");
+ return NGX_ERROR;
+ }
+
+ (void) close(s[0]);
+ (void) close(epfd);
+
+ if (events) {
+ ngx_use_epoll_rdhup = ee.events & EPOLLRDHUP;
+
+ } else {
+ ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
+ "epoll_wait() timedout");
+ }
+
+ ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0,
+ "testing the EPOLLRDHUP flag: %s",
+ ngx_use_epoll_rdhup ? "success" : "fail");
+#endif
+
+ return NGX_OK;
+}
+
+
static void *
ngx_epoll_create_conf(ngx_cycle_t *cycle)
{
diff -r db699978a33f -r f7849bfb6d21 src/event/ngx_event.h
--- a/src/event/ngx_event.h Thu May 12 16:43:19 2016 +0300
+++ b/src/event/ngx_event.h Fri May 13 17:19:23 2016 +0300
@@ -96,6 +96,10 @@ struct ngx_event_s {
* write: available space in buffer when event is ready
* or lowat when event is set with NGX_LOWAT_EVENT flag
*
+ * epoll with EPOLLRDHUP:
+ * accept: 1 if accept many, 0 otherwise
+ * read: 1 if there can be data to read, 0 otherwise
+ *
* iocp: TODO
*
* otherwise:
@@ -196,6 +200,9 @@ typedef struct {


extern ngx_event_actions_t ngx_event_actions;
+#if (NGX_HAVE_EPOLLRDHUP)
+extern ngx_uint_t ngx_use_epoll_rdhup;
+#endif


/*
diff -r db699978a33f -r f7849bfb6d21 src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c Thu May 12 16:43:19 2016 +0300
+++ b/src/http/ngx_http_request.c Fri May 13 17:19:23 2016 +0300
@@ -2752,9 +2752,13 @@ ngx_http_test_reading(ngx_http_request_t

#if (NGX_HAVE_EPOLLRDHUP)

- if ((ngx_event_flags & NGX_USE_EPOLL_EVENT) && rev->pending_eof) {
+ if ((ngx_event_flags & NGX_USE_EPOLL_EVENT) && ngx_use_epoll_rdhup) {
socklen_t len;

+ if (!rev->pending_eof) {
+ return;
+ }
+
rev->eof = 1;
c->error = 1;

diff -r db699978a33f -r f7849bfb6d21 src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c Thu May 12 16:43:19 2016 +0300
+++ b/src/http/ngx_http_upstream.c Fri May 13 17:19:23 2016 +0300
@@ -1222,9 +1222,13 @@ ngx_http_upstream_check_broken_connectio

#if (NGX_HAVE_EPOLLRDHUP)

- if ((ngx_event_flags & NGX_USE_EPOLL_EVENT) && ev->pending_eof) {
+ if ((ngx_event_flags & NGX_USE_EPOLL_EVENT) && ngx_use_epoll_rdhup) {
socklen_t len;

+ if (!ev->pending_eof) {
+ return;
+ }
+
ev->eof = 1;
c->error = 1;

diff -r db699978a33f -r f7849bfb6d21 src/os/unix/ngx_readv_chain.c
--- a/src/os/unix/ngx_readv_chain.c Thu May 12 16:43:19 2016 +0300
+++ b/src/os/unix/ngx_readv_chain.c Fri May 13 17:19:23 2016 +0300
@@ -53,6 +53,20 @@ ngx_readv_chain(ngx_connection_t *c, ngx

#endif

+#if (NGX_HAVE_EPOLLRDHUP)
+
+ if (ngx_event_flags & NGX_USE_EPOLL_EVENT) {
+ ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+ "readv: eof:%d, avail:%d",
+ rev->pending_eof, rev->available);
+
+ if (!rev->available && !rev->pending_eof) {
+ return NGX_AGAIN;
+ }
+ }
+
+#endif
+
prev = NULL;
iov = NULL;
size = 0;
@@ -151,6 +165,24 @@ ngx_readv_chain(ngx_connection_t *c, ngx

#endif

+#if (NGX_HAVE_EPOLLRDHUP)
+
+ if ((ngx_event_flags & NGX_USE_EPOLL_EVENT)
+ && ngx_use_epoll_rdhup)
+ {
+ if (n < size) {
+ if (!rev->pending_eof) {
+ rev->ready = 0;
+ }
+
+ rev->available = 0;
+ }
+
+ return n;
+ }
+
+#endif
+
if (n < size && !(ngx_event_flags & NGX_USE_GREEDY_EVENT)) {
rev->ready = 0;
}
diff -r db699978a33f -r f7849bfb6d21 src/os/unix/ngx_recv.c
--- a/src/os/unix/ngx_recv.c Thu May 12 16:43:19 2016 +0300
+++ b/src/os/unix/ngx_recv.c Fri May 13 17:19:23 2016 +0300
@@ -50,6 +50,21 @@ ngx_unix_recv(ngx_connection_t *c, u_cha

#endif

+#if (NGX_HAVE_EPOLLRDHUP)
+
+ if (ngx_event_flags & NGX_USE_EPOLL_EVENT) {
+ ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+ "recv: eof:%d, avail:%d",
+ rev->pending_eof, rev->available);
+
+ if (!rev->available && !rev->pending_eof) {
+ rev->ready = 0;
+ return NGX_AGAIN;
+ }
+ }
+
+#endif
+
do {
n = recv(c->fd, buf, size, 0);

@@ -101,6 +116,24 @@ ngx_unix_recv(ngx_connection_t *c, u_cha

#endif

+#if (NGX_HAVE_EPOLLRDHUP)
+
+ if ((ngx_event_flags & NGX_USE_EPOLL_EVENT)
+ && ngx_use_epoll_rdhup)
+ {
+ if ((size_t) n < size) {
+ if (!rev->pending_eof) {
+ rev->ready = 0;
+ }
+
+ rev->available = 0;
+ }
+
+ return n;
+ }
+
+#endif
+
if ((size_t) n < size
&& !(ngx_event_flags & NGX_USE_GREEDY_EVENT))
{

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