The nxt_unit_ctx_port_recv() function may return the NXT_UNIT_AGAIN code, in
which case an attempt to reread the message should be made.
The issue was reproduced in load testing with response sizes 16k and up.
In the rare case of a NXT_UNIT_AGAIN result, a buffer of size -1 was processed,
which triggered a 'message too small' alert; after that, the app process was
terminated.
Under high load, a queue synchonization issue may occur, starting from the
steady state when an app queue message is dequeued immediately after it has been
enqueued. In this state, the router always puts the first message in the queue
and is forced to notify the app about a new message in an empty queue using a
socket pair. On the other hand, the application dequeues and processes the
message without reading the notification from the socket, so the socket buffer
overflows with notifications.
The issue was reproduced during Unit load tests. After a socket buffer
overflow, the router is unable to notify the app about a new first message.
When another message is enqueued, a notification is not required, so the queue
grows without being read by the app. As a result, request processing stops.
This patch changes the notification algorithm by counting the notifications in
the pipe instead of getting the number of messages in the queue.
Multithreaded application may create different shared memory segments in
different threads. The segments then passed to different router threads.
Because of this multithreading, the order of adding incoming segments is
not determined and there can be situation when some of the incoming segments
are not initialized yet.
This patch simply adds check for NULL to skip non-initialized segments.
Crash reproduced during load tests with high number of simultaneous
connections (1024 and more).
Ruby threads need to be created with GVL; otherwise, an attempt to access
locked resources may occur, causing a crash.
The issue was occasionally reproduced on Ubuntu 18.04 with Ruby 2.5.1
while running test_ruby_application_threads.
According to Section #3.1.2 of RFC 7230, after the status code
there must be a space even if the reason phrase is empty.
Also, only 3 digits allowed.
This closes#507 issue on GitHub.
