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fix future-scheduling problem related to custodians

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This commit is contained in:
Matthew Flatt 2011-05-16 18:37:32 -06:00
parent 4d4a94a38a
commit 11fa781652
1 changed files with 30 additions and 2 deletions
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28
src/racket/src/future.c
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@ -383,6 +383,12 @@ typedef struct Scheme_Future_Thread_State {
mzrt_sema *worker_can_continue_sema; mzrt_sema *worker_can_continue_sema;
intptr_t runstack_size; intptr_t runstack_size;
/* After a future thread starts, only the runtime thread
modifies the values at these pointers. Future threads
read them without any locks; assembly-level instructions,
such as mfence, ensure that future threads eventually see
changes made by the runtime thread, and the runtime thread
waits as needed. */
volatile int *fuel_pointer; volatile int *fuel_pointer;
volatile uintptr_t *stack_boundary_pointer; volatile uintptr_t *stack_boundary_pointer;
volatile int *need_gc_pointer; volatile int *need_gc_pointer;
@ -809,10 +815,12 @@ void scheme_future_block_until_gc()
for (i = 0; i < fs->thread_pool_size; i++) { for (i = 0; i < fs->thread_pool_size; i++) {
if (fs->pool_threads[i]) { if (fs->pool_threads[i]) {
*(fs->pool_threads[i]->need_gc_pointer) = 1; *(fs->pool_threads[i]->need_gc_pointer) = 1;
if (*(fs->pool_threads[i]->fuel_pointer)) {
*(fs->pool_threads[i]->fuel_pointer) = 0; *(fs->pool_threads[i]->fuel_pointer) = 0;
*(fs->pool_threads[i]->stack_boundary_pointer) += INITIAL_C_STACK_SIZE; *(fs->pool_threads[i]->stack_boundary_pointer) += INITIAL_C_STACK_SIZE;
} }
} }
}
if (cpucount > 1) { if (cpucount > 1) {
/* In principle, we need some sort of fence to ensure that future /* In principle, we need some sort of fence to ensure that future
@ -2103,6 +2111,8 @@ void *worker_thread_future_loop(void *arg)
trigger_added_touches(fs, ft); trigger_added_touches(fs, ft);
record_fevent(FEVENT_COMPLETE, fid); record_fevent(FEVENT_COMPLETE, fid);
fts->thread->current_ft = NULL;
} }
/* Clear stacks */ /* Clear stacks */
@ -2328,6 +2338,24 @@ void scheme_check_future_work()
} else } else
break; break;
} }
/* If any future thread has its fuel revoked (must have been a custodian
shutdown) but doesn't have a future (shutdown future must have been
handled), then we can restore the thread's fuel. Races are
possible, but they should be rare, and they lead at worst to bad
performance. */
{
int i;
for (i = 0; i < fs->thread_pool_size; i++) {
if (fs->pool_threads[i]) {
if (!*(fs->pool_threads[i]->fuel_pointer)
&& !fs->pool_threads[i]->thread->current_ft) {
*(fs->pool_threads[i]->fuel_pointer) = 1;
*(fs->pool_threads[i]->stack_boundary_pointer) -= INITIAL_C_STACK_SIZE;
}
}
}
}
} }
static void future_do_runtimecall(Scheme_Future_Thread_State *fts, static void future_do_runtimecall(Scheme_Future_Thread_State *fts,