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package kamon.trace
/**
* A means of storing and retrieving the currently active Span. The application code execution is always considered to
* contribute to the completion of the operation represented by the currently active Span.
*
* The activation of a Span is of temporary nature and users of this API must ensure that all Scopes created via calls
* to `activate(span)` are timely closed; failing to do so might lead to unexpected behavior. Typically, the same block
* of code designating a Span as currently active will close the created Scope after finishing execution.
*
*/
trait ActiveSpanStorage {
/**
* @return the currently active Span.
*/
def activeSpan(): Span
/**
* Sets
* @param span the Span to be set as currently active.
* @return a [[Scope]] that will finish the designation of the given Span as active once it's closed.
*/
def activate(span: Span): Scope
}
/**
* Encapsulates the state (if any) required to handle the removal of a Span from it's currently active designation.
*
* Typically a Scope will enclose the previously active Span and return the previously active Span when closed,
* although no assumptions are made.
*
*/
trait Scope extends AutoCloseable {
/**
* Removes the currently active Span from the ActiveSpanStorage.
*
*/
def close(): Unit
}
object ActiveSpanStorage {
/**
* A ActiveSpanStorage that uses a [[java.lang.ThreadLocal]] as the underlying storage.
*
*/
final class ThreadLocal extends ActiveSpanStorage {
private val emptySpan = Span.Empty(this)
private val storage: java.lang.ThreadLocal[Span] = new java.lang.ThreadLocal[Span] {
override def initialValue(): Span = emptySpan
}
override def activeSpan(): Span =
storage.get()
override def activate(span: Span): Scope = {
val previouslyActiveSpan = storage.get()
storage.set(span)
new Scope {
override def close(): Unit = {
storage.set(previouslyActiveSpan)
}
}
}
}
object ThreadLocal {
def apply(): ThreadLocal = new ThreadLocal()
}
}
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