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feat (core): Contexts 🧿 put things into perspective!
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# SPDX-License-Identifier: Apache-2.0 | ||
# | ||
# Copyright 2023 The Enola <https://enola.dev> Authors | ||
# | ||
# Licensed under the Apache License, Version 2.0 (the "License"); | ||
# you may not use this file except in compliance with the License. | ||
# You may obtain a copy of the License at | ||
# | ||
# https://www.apache.org/licenses/LICENSE-2.0 | ||
# | ||
# Unless required by applicable law or agreed to in writing, software | ||
# distributed under the License is distributed on an "AS IS" BASIS, | ||
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
# See the License for the specific language governing permissions and | ||
# limitations under the License. | ||
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load("@rules_java//java:defs.bzl", "java_library") | ||
load("//tools/bazel:junit.bzl", "junit_tests") | ||
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java_library( | ||
name = "context", | ||
srcs = glob( | ||
["*.java"], | ||
exclude = ["*Test.java"], | ||
), | ||
visibility = ["//:__subpackages__"], | ||
deps = [ | ||
"//java/dev/enola/common", | ||
"@maven//:com_google_errorprone_error_prone_annotations", | ||
# "@maven//:com_google_guava_guava", | ||
"@maven//:org_jspecify_jspecify", | ||
"@maven//:org_slf4j_slf4j_api", | ||
], | ||
) | ||
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junit_tests( | ||
name = "tests", | ||
srcs = glob(["**/*Test.java"]), | ||
deps = [ | ||
":context", | ||
], | ||
) |
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/* | ||
* SPDX-License-Identifier: Apache-2.0 | ||
* | ||
* Copyright 2024 The Enola <https://enola.dev> Authors | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* https://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
package dev.enola.common.context; | ||
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import static java.util.Objects.requireNonNull; | ||
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import org.jspecify.annotations.Nullable; | ||
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/** | ||
* Contexts 🧿 put things into perspective! | ||
* | ||
* <p>This class is NOT thread safe. Might you want to use {@link TLC} instead? | ||
* | ||
* @author <a href="http://www.vorburger.ch">Michael Vorburger.ch</a> | ||
*/ | ||
public class Context implements AutoCloseable { | ||
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private final @Nullable Context parent; | ||
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private @Nullable Entry last = null; | ||
private boolean closed = false; | ||
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public Context(Context parent) { | ||
this.parent = requireNonNull(parent); | ||
} | ||
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public Context() { | ||
this.parent = null; | ||
} | ||
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/** | ||
* Push, but not too hard… | ||
* | ||
* @param key Key, which must implement {@link #equals(Object)} correctly, and should have a | ||
* useful {@link #toString()}} implementation; in practice, it often IS actually simply a | ||
* {@link String} (but it technically does not necessarily have to be). | ||
* @param value Value to associate with the key. | ||
* @return this, for chaining. | ||
*/ | ||
public Context push(Object key, Object value) { | ||
check(); | ||
last = new Entry(key, value, last); | ||
return this; | ||
} | ||
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/** Get the value for the given key from this or its parent context. */ | ||
public @Nullable Object get(Object key) { | ||
check(); | ||
var current = last; | ||
while (current != null) { | ||
if (current.key.equals(key)) { | ||
return current.value; | ||
} | ||
current = current.previous; | ||
} | ||
if (parent != null) return parent.get(key); | ||
else return null; | ||
} | ||
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// Nota bene: This (kind of) Stack-like data structure (intentionally) | ||
// does not have (need) any pop() ("goes the weasel”) kind of method! | ||
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/** Close this context. Don't use it anymore! */ | ||
@Override | ||
public void close() { | ||
closed = true; | ||
// Free up memory! | ||
last = null; | ||
TLC.reset(parent); | ||
} | ||
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private void check() { | ||
if (closed) { | ||
throw new IllegalStateException("Context already closed"); | ||
} | ||
} | ||
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private static class Entry { | ||
final Object key; | ||
final Object value; | ||
final @Nullable Entry previous; | ||
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Entry(Object key, Object value, @Nullable Entry previous) { | ||
this.key = key; | ||
this.value = value; | ||
this.previous = previous; | ||
} | ||
} | ||
} |
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/* | ||
* SPDX-License-Identifier: Apache-2.0 | ||
* | ||
* Copyright 2024 The Enola <https://enola.dev> Authors | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* https://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
package dev.enola.common.context; | ||
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import com.google.errorprone.annotations.ThreadSafe; | ||
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import org.jspecify.annotations.Nullable; | ||
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/** | ||
* TLC is the Thread Local {@link Context}. (Also known as "Tender Loving Care".) | ||
* | ||
* @author <a href="http://www.vorburger.ch">Michael Vorburger.ch</a> | ||
*/ | ||
@ThreadSafe | ||
public final class TLC { | ||
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private static final ThreadLocal<Context> threadLocalContext = new ThreadLocal<>(); | ||
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/** | ||
* Opens a new (!) {@link Context}, "stacked" over the current one (if any). | ||
* | ||
* <p>This is typically invoked from a try-with-resources, as she returned context must be | ||
* closed again at some point; so . | ||
*/ | ||
public static Context open() { | ||
Context next; | ||
var previous = threadLocalContext.get(); | ||
if (previous != null) { | ||
next = new Context(previous); | ||
} else { | ||
next = new Context(); | ||
} | ||
threadLocalContext.set(next); | ||
return next; | ||
} | ||
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/** See {@link dev.enola.common.context.Context#get(java.lang.Object). */ | ||
public static @Nullable Object get(Object key) { | ||
var tlc = threadLocalContext.get(); | ||
if (tlc == null) { | ||
throw new IllegalStateException("open() first!"); | ||
} | ||
return tlc.get(key); | ||
} | ||
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/* package-local, always keep; never make public! */ | ||
static void reset(@Nullable Context context) { | ||
threadLocalContext.set(context); | ||
} | ||
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private TLC() {} | ||
} |
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/* | ||
* SPDX-License-Identifier: Apache-2.0 | ||
* | ||
* Copyright 2024 The Enola <https://enola.dev> Authors | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* https://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
package dev.enola.common.context; | ||
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import static com.google.common.truth.Truth.assertThat; | ||
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import static org.junit.Assert.assertThrows; | ||
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import org.junit.Test; | ||
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public class TLCTest { | ||
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@Test | ||
public void empty() { | ||
assertThrows(IllegalStateException.class, () -> TLC.get("whatever")); | ||
} | ||
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@Test | ||
public void one() { | ||
try (var ctx = TLC.open()) { | ||
assertThat(ctx.get("unset")).isNull(); | ||
ctx.push("foo", "bar"); | ||
assertThat(TLC.get("foo")).isEqualTo("bar"); | ||
assertThat(ctx.get("unset")).isNull(); | ||
} | ||
} | ||
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@Test | ||
public void nested() { | ||
try (var ctx1 = TLC.open()) { | ||
ctx1.push("foo", "bar"); | ||
assertThat(TLC.get("foo")).isEqualTo("bar"); | ||
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try (var ctx2 = TLC.open()) { | ||
ctx2.push("foo", "baz"); | ||
assertThat(TLC.get("foo")).isEqualTo("baz"); | ||
} | ||
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assertThat(TLC.get("foo")).isEqualTo("bar"); | ||
} | ||
} | ||
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@Test | ||
public void useAfterClose() { | ||
Context ctx = TLC.open(); | ||
ctx.close(); | ||
assertThrows(IllegalStateException.class, () -> ctx.get("whatever")); | ||
} | ||
} |
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/* | ||
* SPDX-License-Identifier: Apache-2.0 | ||
* | ||
* Copyright 2024 The Enola <https://enola.dev> Authors | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* https://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
@NullMarked | ||
package dev.enola.common.context; | ||
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import org.jspecify.annotations.NullMarked; |