Improve open-telemetry/context documentation (#830)

Author: Nevay

ContextInterface.php

@@ -4,39 +4,83 @@
 
 namespace OpenTelemetry\Context;
 
+/**
+ * Immutable execution scoped propagation mechanism.
+ *
+ * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#context
+ */
 interface ContextInterface
 {
     /**
-     * @param non-empty-string $key
+     * Creates a new context key.
      *
-     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/v1.6.1/specification/context/context.md#create-a-key
+     * @param non-empty-string $key name of the key
+     * @return ContextKeyInterface created key
+     *
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#create-a-key
      */
     public static function createKey(string $key): ContextKeyInterface;
 
+    /**
+     * Returns the current context.
+     *
+     * @return ContextInterface current context
+     *
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#get-current-context
+     */
     public static function getCurrent(): ContextInterface;
 
     /**
-     * Makes `$this` the currently active {@see ContextInterface}.
+     * Attaches this context as active context.
+     *
+     * The returned scope has to be {@link ScopeInterface::detach()}ed. In most
+     * cases this should be done using a `try-finally` statement:
+     * ```php
+     * $scope = $context->activate();
+     * try {
+     *     // ...
+     * } finally {
+     *     $scope->detach();
+     * }
+     * ```
+     *
+     * @return ScopeInterface scope to detach the context and restore the previous
+     *         context
+     *
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#attach-context
      */
     public function activate(): ScopeInterface;
 
     /**
-     * This adds a key/value pair to this Context.
+     * Returns a context with the given key set to the given value.
+     *
+     * @template T
+     * @param ContextKeyInterface<T> $key key to set
+     * @param T|null $value value to set
+     * @return ContextInterface a context with the given key set to `$value`
      *
-     * @psalm-template T
-     * @psalm-param ContextKeyInterface<T> $key
-     * @psalm-param T|null $value
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#set-value
      */
     public function with(ContextKeyInterface $key, $value): ContextInterface;
 
+    /**
+     * Returns a context with the given value set.
+     *
+     * @param ImplicitContextKeyedInterface $value value to set
+     * @return ContextInterface a context with the given `$value`
+     *
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#set-value
+     */
     public function withContextValue(ImplicitContextKeyedInterface $value): ContextInterface;
 
     /**
-     * Fetch a value from the Context given a key value.
+     * Returns the value assigned to the given key.
+     *
+     * @template T
+     * @param ContextKeyInterface<T> $key key to get
+     * @return T|null value assigned to `$key`, or null if no such value exists
      *
-     * @psalm-template T
-     * @psalm-param ContextKeyInterface<T> $key
-     * @psalm-return T|null
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#get-value
      */
     public function get(ContextKeyInterface $key);
 }

ContextStorageInterface.php

@@ -6,9 +6,27 @@
 
 interface ContextStorageInterface
 {
+    /**
+     * Returns the current scope.
+     *
+     * @return ContextStorageScopeInterface|null current scope, or null if no
+     *         scope was attached in the current execution unit
+     */
     public function scope(): ?ContextStorageScopeInterface;
 
+    /**
+     * Returns the current context.
+     *
+     * @return ContextInterface current context
+     */
     public function current(): ContextInterface;
 
+    /**
+     * Attaches the context as active context.
+     *
+     * @param ContextInterface $context context to attach
+     * @return ContextStorageScopeInterface scope to detach the context and
+     *         restore the previous context
+     */
     public function attach(ContextInterface $context): ContextStorageScopeInterface;
 }

ContextStorageScopeInterface.php

@@ -8,6 +8,11 @@
 
 interface ContextStorageScopeInterface extends ScopeInterface, ArrayAccess
 {
+    /**
+     * Returns the context associated with this scope.
+     *
+     * @return ContextInterface associated context
+     */
     public function context(): ContextInterface;
 
     /**

README.md

@@ -1 +1,52 @@
 # OpenTelemetry Context
+
+Immutable execution scoped propagation mechanism, for further details see [opentelemetry-specification][1].
+
+## Installation
+
+```shell
+composer require open-telemetry/context
+```
+
+## Usage
+
+### Implicit propagation
+
+```php
+$context = Context::getCurrent();
+// modify context
+$scope = $context->activate();
+try {
+    // run within new context
+} finally {
+    $scope->detach();
+}
+```
+
+It is recommended to use a `try-finally` statement after `::activate()` to ensure that the created scope is properly `::detach()`ed.
+
+## Async applications
+
+### Fiber support
+
+Requires `PHP >= 8.1`, `ext-ffi` and setting the environment variable `OTEL_PHP_FIBERS_ENABLED` to a truthy value. Additionally `vendor/autoload.php` has to be preloaded for non-CLI SAPIs if [`ffi.enable`](https://www.php.net/manual/en/ffi.configuration.php#ini.ffi.enable) is set to `preload`.
+
+### Event loops
+
+Event loops have to restore the original context on callback execution. A basic implementation could look like the following, though implementations should avoid keeping unnecessary references to arguments if possible:
+
+```php
+function bindContext(Closure $closure): Closure {
+    $context = Context::getCurrent();
+    return static function (mixed ...$args) use ($closure, $context): mixed {
+        $scope = $context->activate();
+        try {
+            return $closure(...$args);
+        } finally {
+            $scope->detach();
+        }
+    };
+}
+```
+
+[1]: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#context

ScopeInterface.php

@@ -8,8 +8,11 @@
 
 interface ScopeInterface
 {
+    /** Already detached. */
     public const DETACHED = 1 << (PHP_INT_SIZE << 3) - 1;
+    /** Execution context inactive. */
     public const INACTIVE = 1 << (PHP_INT_SIZE << 3) - 2;
+    /** Not current context. */
     public const MISMATCH = 1 << (PHP_INT_SIZE << 3) - 3;
 
     /**
@@ -23,7 +26,7 @@ interface ScopeInterface
      * @see self::INACTIVE
      * @see self::MISMATCH
      *
-     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/v1.7.0/specification/context/context.md#detach-context
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/README.md#detach-context
      */
     public function detach(): int;
 }

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "open-telemetry/context",
     "description": "Context implementation for OpenTelemetry PHP.",
-    "keywords": ["opentelemetry", "otel", "metrics", "tracing", "logging", "apm", "context"],
+    "keywords": ["opentelemetry", "otel", "context"],
     "type": "library",
     "license": "Apache-2.0",
     "authors": [