[06/20] git commit: TS-2187: use nonblock eventfd in EventNotify

[zw...@apache.org]

TS-2187: use nonblock eventfd in EventNotify

1) Use nonblock eventfd, so that we can tolerate write() failed with
   errno EAGANIN – which is acceptable as the signal receiver will be
   notified eventually in this case.

2) After using nonblock eventfd, read() will not block in wait(). So
   I use epoll_wait() to implement block behavior, just like timedwait().

3) nonblock eventfd can fix a potential problem: if receiver didn't
   read() data immediately, senders might block in write().

Signed-off-by: Yunkai Zhang <qi...@taobao.com>


Project: http://git-wip-us.apache.org/repos/asf/trafficserver/repo
Commit: http://git-wip-us.apache.org/repos/asf/trafficserver/commit/9a6fc2ab
Tree: http://git-wip-us.apache.org/repos/asf/trafficserver/tree/9a6fc2ab
Diff: http://git-wip-us.apache.org/repos/asf/trafficserver/diff/9a6fc2ab

Branch: refs/heads/5.0.x
Commit: 9a6fc2ab6b3147e82dfc229a7158083371d5545e
Parents: 40212d2
Author: Yunkai Zhang <qi...@taobao.com>
Authored: Sun Sep 8 23:35:39 2013 +0800
Committer: Yunkai Zhang <qi...@taobao.com>
Committed: Wed Sep 11 15:18:18 2013 +0800

----------------------------------------------------------------------
 CHANGES               |  2 ++
 lib/ts/EventNotify.cc | 42 +++++++++++++++++++++++++++++++-----------
 lib/ts/EventNotify.h  |  2 +-
 3 files changed, 34 insertions(+), 12 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/trafficserver/blob/9a6fc2ab/CHANGES
----------------------------------------------------------------------
diff --git a/CHANGES b/CHANGES
index d042183..adeb534 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,6 +1,8 @@
                                                          -*- coding: utf-8 -*-
 Changes with Apache Traffic Server 4.1.0
 
+  *) [TS-2187] failed assert `nr == sizeof(uint64_t)` in EventNotify::signal()
+
   *) [TS-2206] The trafficserver RC script does not use absolute path to
    traffic_line binary.
 

http://git-wip-us.apache.org/repos/asf/trafficserver/blob/9a6fc2ab/lib/ts/EventNotify.cc
----------------------------------------------------------------------
diff --git a/lib/ts/EventNotify.cc b/lib/ts/EventNotify.cc
index 3a499b6..feb9ad8 100644
--- a/lib/ts/EventNotify.cc
+++ b/lib/ts/EventNotify.cc
@@ -32,6 +32,7 @@
 
 #ifdef HAVE_EVENTFD
 #include <sys/eventfd.h>
+#include <sys/fcntl.h>
 #include <sys/epoll.h>
 #endif
 
@@ -41,11 +42,13 @@ EventNotify::EventNotify()
   int ret;
   struct epoll_event ev;
 
-  // Don't use noblock here!
-  m_event_fd = eventfd(0, EFD_CLOEXEC);
+  m_event_fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
   if (m_event_fd < 0) {
-    // EFD_CLOEXEC invalid in <= Linux 2.6.27
+    // EFD_NONBLOCK/EFD_CLOEXEC invalid in <= Linux 2.6.27
     m_event_fd = eventfd(0, 0);
+
+    fcntl(m_event_fd, F_SETFD, FD_CLOEXEC);
+    fcntl(m_event_fd, F_SETFL, O_NONBLOCK);
   }
   ink_release_assert(m_event_fd != -1);
 
@@ -69,23 +72,39 @@ EventNotify::signal(void)
 #ifdef HAVE_EVENTFD
   ssize_t nr;
   uint64_t value = 1;
+  //
+  // If the addition would cause the counter’s value of eventfd
+  // to exceed the maximum, write() will fail with the errno EAGAIN,
+  // which is acceptable as the receiver will be notified eventually.
+  //
   nr = write(m_event_fd, &value, sizeof(uint64_t));
-  ink_release_assert(nr == sizeof(uint64_t));
 #else
   ink_cond_signal(&m_cond);
 #endif
 }
 
-void
+int
 EventNotify::wait(void)
 {
 #ifdef HAVE_EVENTFD
-  ssize_t nr;
+  ssize_t nr, nr_fd;
   uint64_t value = 0;
+  struct epoll_event ev;
+
+  do {
+    nr_fd = epoll_wait(m_epoll_fd, &ev, 1, -1);
+  } while (nr_fd == -1 && errno == EINTR);
+
+  if (nr_fd == -1)
+    return errno;
+
   nr = read(m_event_fd, &value, sizeof(uint64_t));
-  ink_release_assert(nr == sizeof(uint64_t));
+  if (nr == sizeof(uint64_t))
+    return 0;
+  else
+    return errno;
 #else
-  ink_cond_wait(&m_cond, &m_mutex);
+  return ink_cond_wait(&m_cond, &m_mutex);
 #endif
 }
 
@@ -115,9 +134,10 @@ EventNotify::timedwait(int timeout) // milliseconds
     return errno;
 
   nr = read(m_event_fd, &value, sizeof(uint64_t));
-  ink_release_assert(nr == sizeof(uint64_t));
-
-  return 0;
+  if (nr == sizeof(uint64_t))
+    return 0;
+  else
+    return errno;
 #else
   ink_timestruc abstime;
   ink_hrtime curtime;

http://git-wip-us.apache.org/repos/asf/trafficserver/blob/9a6fc2ab/lib/ts/EventNotify.h
----------------------------------------------------------------------
diff --git a/lib/ts/EventNotify.h b/lib/ts/EventNotify.h
index b74e3af..7223e6d 100644
--- a/lib/ts/EventNotify.h
+++ b/lib/ts/EventNotify.h
@@ -38,7 +38,7 @@ class EventNotify
 public:
   EventNotify();
   void signal(void);
-  void wait(void);
+  int wait(void);
   int timedwait(int timeout); // milliseconds
   void lock(void);
   bool trylock(void);