我对在 Java 中的线程之间安全地共享数组感到困惑，特别是内存栅栏和关键字synchronized.
此问答很有帮助，但不能回答我的所有问题：Java 数组：同步 + 原子*，还是同步就足够了？
以下是演示该问题的示例代码。假设有一个填充SharedTablevia 方法的工作线程池add(...)。在所有工作线程完成后，最后一个线程读取并保存数据。
演示问题的示例代码：
public final class SharedTable {
// Column-oriented data entries
private final String[] data1Arr;
private final int[] data2Arr;
private final long[] data3Arr;
private final AtomicInteger nextIndex;
public SharedTable(int size) {
this.data1Arr = new String[size];
this.data2Arr = new int[size];
this.data3Arr = new long[size];
this.nextIndex = new AtomicInteger(0);
}
// Thread-safe: Called by worker threads
public void addEntry(String data1, int data2, long data3) {
final int index = nextIndex.getAndIncrement();
data1Arr[index] = data1;
data2Arr[index] = data2;
data3Arr[index] = data3;
}
// Not thread-safe: Called by clean-up/joiner/collator thread...
// after worker threads are complete
public void save() {
// Does this induce a full memory fence to ensure thread-safe reading of
synchronized (this) {
final int usedSide = nextIndex.get();
for (int i = 0; i < usedSide; ++i) {
final String data1 = data1Arr[i];
final int data2 = data2Arr[i];
final long data3 = data3Arr[i];
// TODO: Save data here
}
}
}
}
上面的示例代码也可以使用 来实现Atomic*Array，它充当“易失性值/引用的数组”。
public final class SharedTable2 {
// Column-oriented data entries
private final AtomicReferenceArray<String> data1Arr;
private final AtomicIntegerArray data2Arr;
private final AtomicLongArray data3Arr;
private final AtomicInteger nextIndex;
public SharedTable2(int size) { ... }
// Thread-safe: Called by worker threads
public void addEntry(String data1, int data2, long data3) {
final int index = nextIndex.getAndIncrement();
data1Arr.set(index, data1);
...
}
// Not thread-safe: Called by clean-up/joiner/collator thread...
// after worker threads are complete
public void save() {
final int usedSide = nextIndex.get();
for (int i = 0; i < usedSide; ++i) {
final String data1 = data1Arr.get(i);
final int data2 = data2Arr.get(i);
final long data3 = data3Arr.get(i);
// TODO: Save data here
}
}
}
SharedTable线程安全（和缓存一致）吗？- （很多？
SharedTable）效率更高，因为只需要一个内存栅栏，而SharedTable2每次调用都调用一个内存栅栏Atomic*Array.set(...)？
如果有帮助，我将在 64 位 x86 硬件（Windows 和 Linux）上使用 Java 8。