processutils.execute causes high CPU usage under eventlet

[YAMADA Hideki]

It happens when processutils.execute has large stdin data.

We can reproduce the bug with this code snippet:

---
import eventlet
eventlet.monkey_patch()

from oslo_concurrency import processutils

# 100MB data
data = '0123456789' * 10 * 1024 * 1024
processutils.execute('cat', process_input=data)
---

The result is:

---
$ time python /tmp/test.py

real 0m14.839s
user 0m12.614s
sys 0m5.145s
---

And 100% CPU usage while running.

Without eventlet:

---
$ time python /tmp/test.py

real 0m0.367s
user 0m0.208s
sys 0m0.335s
---