On 29 March 2006 17:21, Claus Reinke wrote:
all of the concurrency implementations discussed so far seem to be based on a mixture of preemptive and non-premptive scheduling. context-switches happen only on specific events, which every thread will usually engage in, although it need not always do so:
1 only calls to yield 2 any calls to concurrency library api 3 any allocation
Not true - in GHC with SMP a thread doing no allocation can be running concurrently with any number of other threads. It's only the single-threaded implementation that has this bug where a thread that doesn't allocate can starve the other threads. In fact, even on a uniprocessor, you can use GHC's SMP mode to work around the bug by pretending you have 2 CPUs. GHC's SMP mode is truly preemptive, operations from multiple threads can be arbitrarily interleaved. So let's stop saying that all known implementations are non-preemptive, please ;-) Cheers, Simon