[jira] [Created] (LOG4J2-2671) Improve the performance of adding and removing multiple values from the ThreadContext

["Luke Butters (JIRA)" <ji...@apache.org>]

Luke Butters created LOG4J2-2671:
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             Summary: Improve the performance of adding and removing multiple values from the ThreadContext
                 Key: LOG4J2-2671
                 URL: https://issues.apache.org/jira/browse/LOG4J2-2671
             Project: Log4j 2
          Issue Type: Improvement
            Reporter: Luke Butters


I notice in profiling that a bunch of time is spent under ThreadContext specifically in DefaultThreadContextMap.

What my code does is put a few things into the map e.g.
{code:java}
ThreadContext.put("a", "b");{code}
This actually results in [DefaultThreadContextMap|https://github.com/apache/logging-log4j2/blob/master/log4j-api/src/main/java/org/apache/logging/log4j/spi/DefaultThreadContextMap.java#L83] creating a copy of the existing map, updating that copy and setting it back. So if I want to set 5 things we end up copying the map 4 times.
This also happens when calling:
{code:java}
ThreadContext.remove("a");{code}

What could be done instead is for {{ThreadContext}} to take multiple values {{similar to the exiting }}{{putAll}} available on {{Map}} that way I can pass in all values at once avoiding making (n -1) copies of the Map. It might make sense for this method to take{{}} a {{Collection}} of {{Map.Entry}} as that way the caller doesn't need to construct a Map and can instead construct a cheaper list of Entries to be added to the map.

some sample code of how this would look:


{code:java}
    public void putAll(Collection<Map.Entry<String, String>> toAdd) {
        if (!useMap) {
            return;
        }
        Map<String, String> map = localMap.get();
        map = map == null ? new HashMap<String, String>() : new HashMap<>(map);
        for(Map.Entry<String, String> e : toAdd) {
            map.put(e.getKey(), e.getValue());
        }
        localMap.set(Collections.unmodifiableMap(map));
    }{code}


The remove method should also be improved to take a List entries that way we can avoid making multiple copies of the map an example of how this might look:


{code:java}
    public void remove(final Collection<String> keys) {
        final Map<String, String> map = localMap.get();
        if (map != null) {
            final Map<String, String> copy = new HashMap<>(map);
            for(String key : keys) {
                copy.remove(key);
            }
            localMap.set(Collections.unmodifiableMap(copy));
        }
    }{code}
 

Running a test which attempts to add 5 values and then remove those 5 values 1 million times, repeated ten times. I then averaged the results of how long that took for all ten results to come up with:
*current:* 1093ms

*new:* 310ms



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