TA貢獻(xiàn)1824條經(jīng)驗 獲得超8個贊
理想的 trySplit 方法有效地（無需遍歷）將其元素精確地一分為二，從而實現(xiàn)平衡的并行計算。許多偏離這一理想的方法仍然非常有效；例如，僅對近似平衡的樹進(jìn)行近似分裂，或者對于葉子節(jié)點可能包含一個或兩個元素的樹，未能進(jìn)一步分裂這些節(jié)點。然而，平衡的大偏差和/或過度低效的 trySplit 機制通常會導(dǎo)致并行性能不佳。
以及帶有注釋的方法結(jié)構(gòu)
public Spliterator<T> trySplit() {
int lo = origin; // divide range in half
int mid = ((lo + fence) >>> 1) & ~1; // force midpoint to be even
if (lo < mid) { // split out left half
origin = mid; // reset this Spliterator's origin
return new TaggedArraySpliterator<>(array, lo, mid);
}
else // too small to split
return null;
}
更多信息請閱讀https://docs.oracle.com/javase/8/docs/api/java/util/Spliterator.html
TA貢獻(xiàn)1796條經(jīng)驗 獲得超10個贊
這是實現(xiàn) Spliterator 的示例。
public class Payment {
private String category;
private double amount;
public Payment(double amount, String category) {
this.amount = amount;
this.category = category;
}
public String getCategory() {
return category;
}
public double getAmount() {
return amount;
}
}
TrySplit 實現(xiàn)：
import java.util.List;
import java.util.Spliterator;
import java.util.function.Consumer;
public class PaymentBatchSpliterator implements Spliterator<Payment> {
private List<Payment> paymentList;
private int current;
private int last; // inclusive
public PaymentBatchSpliterator(List<Payment> payments) {
this.paymentList = payments;
last = paymentList.size() - 1;
}
public PaymentBatchSpliterator(List<Payment> payments, int start, int last) {
this.paymentList = payments;
this.current = start;
this.last = last;
}
@Override
public boolean tryAdvance(Consumer<? super Payment> action) {
if (current <= last) {
action.accept(paymentList.get(current));
current++;
return true;
}
return false;
}
@Override
public Spliterator<Payment> trySplit() {
if ((last - current) < 100) {
return null;
}
// first stab at finding a split position
int splitPosition = current + (last - current) / 2;
// if the categories are the same, we can't split here, as we are in the middle of a batch
String categoryBeforeSplit = paymentList.get(splitPosition-1).getCategory();
String categoryAfterSplit = paymentList.get(splitPosition).getCategory();
// keep moving forward until we reach a split between categories
while (categoryBeforeSplit.equals(categoryAfterSplit)) {
splitPosition++;
categoryBeforeSplit = categoryAfterSplit;
categoryAfterSplit = paymentList.get(splitPosition).getCategory();
}
// safe to create a new spliterator
PaymentBatchSpliterator secondHalf = new PaymentBatchSpliterator(paymentList,splitPosition,last);
// reset our own last value
last = splitPosition - 1;
return secondHalf;
}
@Override
public long estimateSize() {
return last - current;
}
@Override
public int characteristics() {
return 0;
}
}
是來自 GitHub參考的示例
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