On 01/08/13 08:43, Andrew Haley wrote:
One random thought. Linux x86 has very fast access to thread local variables: it's just a segment prefix on a load instruction. I wonder if the JVM could utilize something like this and so improve performance for thread locals that don't require non-null initial values.
Thanks. Yes, I've had discussions with various people over the years about somehow exploiting native thread-local support for simple scalars. I don't think there is a great scheme to be had here though. Problems include (1) fixed arena sizes on some/most platforms. (2) no good way to coordinate slot-grabbing with native uses (3) no good way to relinquish (4) no good emulation scheme for systems without support But mostly: The space for "permanent" thread-locals needs to be placed somewhere; why not choose the place that presents the fewest logistics problems? Note that class java.lang.Thread is only the visible tip of the iceberg of per-thread storage on systems. so adding 16bytes is all but undetectable. -Doug
