Upon every task completion, PythonAccumulatorParam constructs a new socket to the Accumulator server running inside the pyspark daemon. This can cause a buildup of used ephemeral ports from sockets in the TIME_WAIT termination stage, which will cause the SparkContext to crash if too many tasks complete too quickly. We ran into this bug with 17k tasks completing in 15 seconds.
This bug can be fixed outside of Spark by ensuring these properties are set (on a linux server);
echo "1" > /proc/sys/net/ipv4/tcp_tw_reuse
echo "1" > /proc/sys/net/ipv4/tcp_tw_recycle
or by adding the SO_REUSEADDR option to the Socket creation within Spark.