Thread safety on `producer.metrics()`

[emeric254]

It's seems there is a thread safety issue when retrieving producer metrics from an independent thread.

We did not encounter this behavior on consumers but we checked the library code it should be affected too.

This is the error we got when reading metrics for a producer:

File "...\lib\site-packages\kafka\producer\kafka.py", line 722, in metrics
    for k, v in six.iteritems(self._metrics.metrics):
RuntimeError: dictionary changed size during iteration

Here is the current faulty code in the producer (note the direct use of self._metrics.metrics):

def metrics(self, raw=False):
    [...]
    metrics = {}
    for k, v in six.iteritems(self._metrics.metrics):
        if k.group not in metrics:
            metrics[k.group] = {}
        if k.name not in metrics[k.group]:
            metrics[k.group][k.name] = {}
        metrics[k.group][k.name] = v.value()
    return metrics

One solution is to return a copy of actual metrics :

def metrics(self, raw=False):
    [...]
    metrics = {}
    for k, v in six.iteritems(self._metrics.metrics.copy()):
        if k.group not in metrics:
            metrics[k.group] = {}
        if k.name not in metrics[k.group]:
            metrics[k.group][k.name] = {}
        metrics[k.group][k.name] = v.value()
    return metrics

I will create a PR for this

[emeric254]

see PR #1682

[tvoinarovskyi]

Well, it makes sense for Producer, as we declare it as Thread safe for sending.

[tvoinarovskyi]

Closing this, as the fix was merged. Thanks for the contribution!