presto-main/src/main/java/io/prestosql/execution/MemoryRevokingScheduler.java/MemoryRevokingScheduler/runMemoryRevoking
class MemoryRevokingScheduler:    private synchronized void runMemoryRevoking()
    {
        if (checkPending.getAndSet(false)) {
            Collection<SqlTask> sqlTasks = null;
            for (MemoryPool memoryPool : memoryPools) {
                if (!memoryRevokingNeeded(memoryPool)) {
                    continue;
                }

                if (sqlTasks == null) {
                    sqlTasks = requireNonNull(currentTasksSupplier.get());
                }

                requestMemoryRevoking(memoryPool, sqlTasks);
            }
        }
    }