是否可以安全地假设addAndGet之前的代码将始终在此调用之前执行，即JVM将不重新排序AtomicInteger调用的指令？
如果是，可以安全地假设检查同一if (a.compareAndSet(0, -1))实例（例如addAndGet）的状态的其他线程将在 public string digest()
{
String retVal = "";
try
{
string url = "https://YourSite.com/";
HttpClient client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true });
client.BaseAddress = new System.Uri(url);
string cmd = "_api/contextinfo";
client.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");
client.DefaultRequestHeaders.Add("ContentType", "application/json");
client.DefaultRequestHeaders.Add("ContentLength", "0");
StringContent httpContent = new StringContent("");
var response = client.PostAsync(cmd, httpContent).Result;
if (response.IsSuccessStatusCode)
{
string content = response.Content.ReadAsStringAsync().Result;
JsonObject val = JsonValue.Parse(content).GetObject();
JsonObject d = val.GetNamedObject("d");
JsonObject wi = d.GetNamedObject("GetContextWebInformation");
retVal = wi.GetNamedString("FormDigestValue");
}
}
catch
{ }
return retVal;
}
FileOpenPicker picker = new FileOpenPicker();
picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
picker.ViewMode = PickerViewMode.Thumbnail;
// Filter to include a sample subset of file types.
picker.FileTypeFilter.Clear();
picker.FileTypeFilter.Add(".bmp");
picker.FileTypeFilter.Add(".png");
picker.FileTypeFilter.Add(".jpeg");
picker.FileTypeFilter.Add(".jpg");
// Open the file picker.
StorageFile path = await picker.PickSingleFileAsync();
if (path != null)
{
string url = "https://YourSite.com/Subsite/";
HttpClient client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true });
client.BaseAddress = new System.Uri(url);
client.DefaultRequestHeaders.Clear();
client.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");
client.DefaultRequestHeaders.Add("X-RequestDigest", digest());
client.DefaultRequestHeaders.Add("X-HTTP-Method", "POST");
client.DefaultRequestHeaders.Add("binaryStringRequestBody", "true");
IRandomAccessStream fileStream = await path.OpenAsync(FileAccessMode.Read);
var reader = new DataReader(fileStream.GetInputStreamAt(0));
await reader.LoadAsync((uint)fileStream.Size);
Byte[] content = new byte[fileStream.Size];
reader.ReadBytes(content);
ByteArrayContent file = new ByteArrayContent(content);
HttpResponseMessage response = await client.PostAsync("_api/web/lists/getByTitle(@TargetLibrary)/RootFolder/Files/add(url=@TargetFileName,overwrite='true')?@TargetLibrary='Project Photos'&@TargetFileName='TestUpload.jpg'", file);
response.EnsureSuccessStatusCode();
if (response.IsSuccessStatusCode)
{ }
}
调用之前看到第一个线程已更改的所有内容？
答案 0 :(得分：6)
假设之前的代码（AtomicInteger a）.addAndGet（-1）将始终在此调用之前执行，即JVM 不会重新排序addAndGet调用的指令吗？
是的，没错。 addAndGet将发出易失性存储（或类似），因此其他负载和存储不能在其下重新排序。
编辑：感谢Soitrios链接https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/package-summary.html，这表明您已经建立了订购。
- get具有读取volatile变量的记忆效应。
- set具有写入（赋值）volatile变量的记忆效应。
- compareAndSet和所有其他读取和更新操作（如getAndIncrement）具有读取和写入volatile变量的内存效果。