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The Cancellation library
========================
Intro
-----
This small library provides primitives for implementation of a cooperative cancellation of long running or asynchronous operations.
The design has been copied from the well-known CancellationTokenSource/CancellationToken classes of the .NET Framework
To use the library include `cancellation_token.h`.
Examples
--------
1. Simple check for cancellation
```c++
void LongRunningOperation(TCancellationToken token) {
...
if (token.IsCancellationRequested()) {
return;
}
...
}
TCancellationTokenSource source;
TThread thread([token = source.Token()]() { LongRunningOperation(std::move(token)); });
thread.Start();
...
source.Cancel();
thread.Join();
```
2. Exit via an exception
```c++
void LongRunningOperation(TCancellationToken token) {
try {
for (;;) {
...
token.ThrowIfCancellationRequested();
...
}
} catch (TOperationCancelledException const&) {
return;
} catch (...) {
Y_FAIL("Never should be there")
}
}
TCancellationTokenSource source;
TThread thread([token = source.Token()]() { LongRunningOperation(std::move(token)); });
thread.Start();
...
source.Cancel();
thread.Join();
```
3. Periodic poll with cancellation
```c++
void LongRunningOperation(TCancellationToken token) {
while (!token.Wait(PollInterval)) {
...
}
}
TCancellationTokenSource source;
TThread thread([token = source.Token()]() { LongRunningOperation(std::move(token)); });
thread.Start();
...
source.Cancel();
thread.Join();
```
4. Waiting on the future
```c++
TFuture<void> InnerOperation();
TFuture<void> OuterOperation(TCancellationToken token) {
return WaitAny(FirstOperation(), token.Future())
.Apply([token = std::move(token)](auto&&) {
token.ThrowIfCancellationRequested();
});
}
TCancellationTokenSource source;
auto future = OuterOperation();
...
source.Cancel()
...
try {
auto value = future.ExtractValueSync();
} catch (TOperationCancelledException const&) {
// cancelled
}
```
5. Using default token when no cancellation needed
```c++
void LongRunningOperation(TCancellationToken token) {
...
if (token.IsCancellationRequested()) {
return;
}
...
}
// We do not want to cancel the operation. So, there is no need to create a cancellation token source
LongRunningOperation(TCancellationToken::Default);
```
|
