IOError: [Errno 11] Resource temporarily unavailable

[marc1n]

uWSGI is failing when logging big string to stream logger (got EAGAIN from logger socket)

$ uwsgi --version
2.0.13.1

$ uname -a
Linux 4.4.0-22-generic #40-Ubuntu SMP Thu May 12 22:03:46 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

uwsgi.ini:

[uwsgi]
http-socket = :9090
processes = 2
logger = file:/tmp/uwsgi.log
log-master-stream = true 
wsgi-file=app.py

app.py:

def application(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    print 'x\n' * (1024 * 1024)
    return ['Hello']

1. Run uWSGI:
   $ pkill -9 uwsgi; pgrep uwsgi; rm -f /tmp/uwsgi.log; uwsgi --ini=uwsgi.ini
   [uWSGI] getting INI configuration from uwsgi.ini
2. From other terminal (sometimes error does not happen):
   $ curl http://localhost:9090; tail /tmp/uwsgi.log
   x
   x
   x
   x
   x
   Traceback (most recent call last):
   File "app.py", line 7, in application
   print big_log
   IOError: [Errno 11] Resource temporarily unavailable
   [pid: 23479|app: 0|req: 1/2] 127.0.0.1 () {24 vars in 249 bytes} [Wed May 25 11:25:27 2016] GET / => generated 0 bytes in 0 msecs (HTTP/1.1 200) 1 headers in 45 bytes (0 switches on core 0)

[marc1n]

Any ideas?

[marc1n]

Error happened event if I print 128kB data:

def application(environ, start_response):
start_response('200 OK', [('Content-Type', 'text/plain')])
print 'x\n' * (128 * 1024)
return ['Hello']

pkill -9 uwsgi; pgrep uwsgi; rm -f /tmp/uwsgi.log; uwsgi --ini=uwsgi.ini

curl http://localhost:9090 && tail /tmp/uwsgi.log

x
x
x
x
x
x
x
x
IOError: [Errno 11] Resource temporarily unavailable
[pid: 14245|app: 0|req: 1/1] 127.0.0.1 () {24 vars in 244 bytes} [Tue Oct 25 12:56:44 2016] GET / => generated 0 bytes in 0 msecs (HTTP/1.1 200) 1 headers in 45 bytes (0 switches on core 0)

[marc1n]

Probable reason is that uWSGI set stdout stream as non blocking if we set 'logger' option.

Errno 11 == EAGAIN and https://linux.die.net/man/2/send:
When the message does not fit into the send buffer of the socket, send() normally blocks, unless the socket has been placed in nonblocking I/O mode. In nonblocking mode it would fail with the error EAGAIN or EWOULDBLOCK in this case.

[marc1n]

See: https://stackoverflow.com/questions/41377059/how-to-solve-errno-11-resource-temporarily-unavailable-using-uwsgi-nginx

[marc1n]

If the option log-master-stream is false than there is other error: "[Errno 90] Message too long" (issue #1265):

Traceback (most recent call last):
File "app.py", line 3, in application
print 'x\n' * (1024 * 1024)
IOError: [Errno 90] Message too long

[marc1n]

I've finally found a workaround. Set option log-master-bufsize to value bigger than printed string (for example 2048577). Default is 8192.