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api: Add a Supplier overload to Context #12935

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api: Add a Supplier overload to Context
carl-mastrangelo Jul 27, 2026
55b44a9
Merge branch 'master' into contextsupplier
carl-mastrangelo Jul 28, 2026
f7faff8
must use
carl-mastrangelo Jul 30, 2026
6164702
Merge branch 'master' into contextsupplier
carl-mastrangelo Jul 30, 2026
afc76e4
Add experimental
carl-mastrangelo Jul 30, 2026
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16 changes: 16 additions & 0 deletions api/src/context/java/io/grpc/Context.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;

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package java.util.function does not exist
import java.util.logging.Level;
import java.util.logging.Logger;

Expand Down Expand Up @@ -554,6 +555,21 @@
}
}

/**
* Immediately supply a value from a {@link Supplier} with this context as the
* {@link #current} context.
* @param supplier {@link Supplier} to use to produce the value.
* @return result of supplier.
*/
public <V> V supply(Supplier<V> supplier) {

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Context previous = attach();
try {
return supplier.get();
} finally {
detach(previous);
}
}

/**
* Wrap a {@link Runnable} so that it executes with this context as the {@link #current} context.
*/
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41 changes: 41 additions & 0 deletions api/src/test/java/io/grpc/ContextTest.java
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Expand Up @@ -49,6 +49,7 @@
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.LogRecord;
Expand Down Expand Up @@ -553,6 +554,46 @@ public Object call() {
current.detach(Context.ROOT);
}

@Test
public void testSupply() throws Exception {

@kannanjgithub kannanjgithub Aug 10, 2026

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This single test is testing multiple different behaviors. We can rewrite it into 3 different behavior driven tests each following the Given-When-Then structure for testing each behavior:

supply_executesSupplierUnderTargetContextAndRestoresPrevious
supply_whenContextIsAlreadyCurrent_executesAndMaintainsContext
supply_whenSupplierThrows_propagatesExceptionAndRestoresPreviousContext

@carl-mastrangelo carl-mastrangelo Aug 10, 2026

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I think it would be better for the maintainers to take on that task. I wrote the test to match the existing style, and since I don't know your preferences, I think it would be better for you to adjust it the way you want.

Claude should be able to easily adjust and split these tests. How about we continue with the PR as is and the tests can be adjusted after?

Context base = Context.current().withValue(PET, "cat");
Context current = Context.current().withValue(PET, "fish");
current.attach();

final Object ret = new Object();
Supplier<Object> supplier = new Supplier<Object>() {
@Override
public Object get() {
runner.run();
return ret;
}
};

assertSame(ret, base.supply(supplier));
assertSame(base, observed);
assertSame(current, Context.current());

assertSame(ret, current.supply(supplier));
assertSame(current, observed);
assertSame(current, Context.current());

final TestError err = new TestError();
try {

@panchenko panchenko Jul 28, 2026

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TestError caught = assertThrows(TestError.class, ...

@carl-mastrangelo carl-mastrangelo Jul 28, 2026

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If you feel strongly I can, but I was keeping the style of the tests around it.

@panchenko panchenko Jul 30, 2026

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assertThrows() was not available back then, worth using in new code

base.supply(new Supplier<Object>() {
@Override
public Object get() {
throw err;
}
});
fail("Excepted exception");
} catch (TestError ex) {
assertSame(err, ex);
}
assertSame(current, Context.current());

current.detach(Context.ROOT);
}

@Test
public void currentContextExecutor() {
QueuedExecutor queuedExecutor = new QueuedExecutor();
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