Is it OK to modify different histogram bins from different threads using `AddBinContent`?

Newbie
1

If I don’t care about mean/stddev/entries consistency.

2

HI,
I don’t think is safe because two updates of the same bin can happen at the same time and then the result might not be correct. I would create an histogram for each thread or lock when calling the AddBinContent function (but will kill all performances)

Lorenzo

3

The sets of bins for each thread are not overlapping.

4

The playground for disaster is greater than the size of a bin content storage - it’s a cache line. But in practice we are aware of people doing what you say, and they survive :wink: But it’s risky, there’s no guarantee that the result is guaranteed to be correct. As Lorenzo said, you could use TThreadedObject https://root.cern/doc/master/classROOT_1_1TThreadedObject.html

5

I can random shuffle the bin numbers to the threads won’t content for a cache line.

is very slow.

6

TThreadedObject is much faster than locking a single histogram :slight_smile: It’s all relative…

I don’t understand the random shuffle comment - but that’s not needed for it to work! Glad you have a solution!