Re: Followup to "Serious concurrency problems on fast systems"

Lew <>
Mon, 05 Jul 2010 23:09:58 -0400
Kevin McMurtrie wrote:

ALL thread interaction on a multi-CPU system is slow. Try 10 threads
writing to adjacent memory in a shared array compared to 10 threads
writing to memory in their own array. Not only is that a baseline for
all concurrency techniques, but it can hinder performance in non-obvious

In my benchmarks, a 'synchronized' block has less overhead than all of
the Java 1.5 lock mechanisms. If you must alter a set of data in a
consistent state, it seems to be the way to go.

Robert Klemme wrote:

The demo code shows that although you can get pretty fast with
synchronized there are faster alternatives. Especially the variant with
an AtomicReference (or plain volatile) is dramatically faster. It
depends on the situation what to choose. synchronize is not the one size
fits all solution to concurrency issues.

Kevin McMurtrie wrote:

Its downside is that a
thread can use up its CPU quanta while holding the lock and everything
else piles up for a while. Java 1.5 locks give you options for shared
read locks and fail-fast lock acquisition that may reduce blocking.

Knute Johnson wrote:

Just as there is a diminishing return to more threads.

Or more CPUs on a board, or more nodes in a cluster, or more programmers on a
team, ...


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