[[concurrency]]
= Concurrency Support

In most environments, Security is stored on a per-`Thread` basis.
This means that when work is done on a new `Thread`, the `SecurityContext` is lost.
Spring Security provides some infrastructure to help make this much easier to manage.
Spring Security provides low-level abstractions for working with Spring Security in multi-threaded environments.
In fact, this is what Spring Security builds on to integrate with xref:servlet/integrations/servlet-api.adoc#servletapi-start-runnable[`AsyncContext.start(Runnable)`] and xref:servlet/integrations/mvc.adoc#mvc-async[Spring MVC Async Integration].

== DelegatingSecurityContextRunnable

One of the most fundamental building blocks within Spring Security's concurrency support is the `DelegatingSecurityContextRunnable`.
It wraps a delegate `Runnable` to initialize the `SecurityContextHolder` with a specified `SecurityContext` for the delegate.
It then invokes the delegate `Runnable`, ensuring to clear the `SecurityContextHolder` afterwards.
The `DelegatingSecurityContextRunnable` looks something like this:

[source,java]
----
public void run() {
try {
	SecurityContextHolder.setContext(securityContext);
	delegate.run();
} finally {
	SecurityContextHolder.clearContext();
}
}
----

While very simple, it makes it seamless to transfer the `SecurityContext` from one `Thread` to another.
This is important since, in most cases, the `SecurityContextHolder` acts on a per-`Thread` basis.
For example, you might have used Spring Security's xref:servlet/appendix/namespace/method-security.adoc#nsa-global-method-security[`<global-method-security>`] support to secure one of your services.
You can now transfer the `SecurityContext` of the current `Thread` to the `Thread` that invokes the secured service.
The following example show how you might do so:

[source,java]
----
Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

SecurityContext context = SecurityContextHolder.getContext();
DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable, context);

new Thread(wrappedRunnable).start();
----

The preceding code:

* Creates a `Runnable` that invokes our secured service.
Note that it is not aware of Spring Security.
* Obtains the `SecurityContext` that we wish to use from the `SecurityContextHolder` and initializes the `DelegatingSecurityContextRunnable`.
* Uses the `DelegatingSecurityContextRunnable` to create a `Thread`.
* Starts the `Thread` we created.

Since it is common to create a `DelegatingSecurityContextRunnable` with the `SecurityContext` from the `SecurityContextHolder`, there is a shortcut constructor for it.
The following code has the same effect as the preceding code:


[source,java]
----
Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable);

new Thread(wrappedRunnable).start();
----

The code we have is simple to use, but it still requires knowledge that we are using Spring Security.
In the next section we will take a look at how we can utilize `DelegatingSecurityContextExecutor` to hide the fact that we are using Spring Security.

== DelegatingSecurityContextExecutor

In the previous section, we found that it was easy to use the `DelegatingSecurityContextRunnable`, but it was not ideal since we had to be aware of Spring Security to use it.
Now we look at how `DelegatingSecurityContextExecutor` can shield our code from any knowledge that we are using Spring Security.

The design of `DelegatingSecurityContextExecutor` is similar to that of `DelegatingSecurityContextRunnable`, except that it accepts a delegate `Executor` instead of a delegate `Runnable`.
The following example shows how to use it:

[source,java]
----
SecurityContext context = SecurityContextHolder.createEmptyContext();
Authentication authentication =
	UsernamePasswordAuthenticationToken.authenticated("user","doesnotmatter", AuthorityUtils.createAuthorityList("ROLE_USER"));
context.setAuthentication(authentication);

SimpleAsyncTaskExecutor delegateExecutor =
	new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor, context);

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

executor.execute(originalRunnable);
----

This code:

Note that, in this example, we create the `SecurityContext` by hand.
However, it does not matter where or how we get the `SecurityContext` (for example, we could obtain it from the `SecurityContextHolder`).
* Creates a `delegateExecutor` that is in charge of executing submitted `Runnable` objects.
* Finally, we create a `DelegatingSecurityContextExecutor`, which is in charge of wrapping any `Runnable` that is passed into the `execute` method with a `DelegatingSecurityContextRunnable`.
It then passes the wrapped `Runnable` to the `delegateExecutor`.
In this case, the same `SecurityContext` is used for every `Runnable` submitted to our `DelegatingSecurityContextExecutor`.
This is nice if we run background tasks that need to be run by a user with elevated privileges.
* At this point, you may ask yourself, "`How does this shield my code of any knowledge of Spring Security?`" Instead of creating the `SecurityContext` and the `DelegatingSecurityContextExecutor` in our own code, we can inject an already initialized instance of `DelegatingSecurityContextExecutor`.

Consider the following example:

[source,java]
----
@Autowired
private Executor executor; // becomes an instance of our DelegatingSecurityContextExecutor

public void submitRunnable() {
Runnable originalRunnable = new Runnable() {
	public void run() {
	// invoke secured service
	}
};
executor.execute(originalRunnable);
}
----

Now our code is unaware that the `SecurityContext` is being propagated to the `Thread`, the `originalRunnable` is run, and the `SecurityContextHolder` is cleared out.
In this example, the same user is being used to run each thread.
What if we wanted to use the user from `SecurityContextHolder` (that is, the currently logged in-user) at the time we invoked `executor.execute(Runnable)` to process `originalRunnable`?
You can do so by removing the `SecurityContext` argument from our `DelegatingSecurityContextExecutor` constructor:

[source,java]
----
SimpleAsyncTaskExecutor delegateExecutor = new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor);
----

Now, any time `executor.execute(Runnable)` is run, the `SecurityContext` is first obtained by the `SecurityContextHolder` and then that `SecurityContext` is used to create our `DelegatingSecurityContextRunnable`.
This means that we are running our `Runnable` with the same user that was used to invoke the `executor.execute(Runnable)` code.

== Spring Security Concurrency Classes

See the {security-api-url}index.html[Javadoc] for additional integrations with both the Java concurrent APIs and the Spring Task abstractions.
They are self-explanatory once you understand the previous code.

* {security-api-url}org/springframework/security/concurrent/DelegatingSecurityContextCallable.html[`DelegatingSecurityContextCallable`]
* {security-api-url}org/springframework/security/concurrent/DelegatingSecurityContextExecutor.html[`DelegatingSecurityContextExecutor`]
* {security-api-url}org/springframework/security/concurrent/DelegatingSecurityContextExecutorService.html[`DelegatingSecurityContextExecutorService`]
* {security-api-url}org/springframework/security/concurrent/DelegatingSecurityContextRunnable.html[`DelegatingSecurityContextRunnable`]
* {security-api-url}org/springframework/security/concurrent/DelegatingSecurityContextScheduledExecutorService.html[`DelegatingSecurityContextScheduledExecutorService`]
* {security-api-url}org/springframework/security/scheduling/DelegatingSecurityContextSchedulingTaskExecutor.html[`DelegatingSecurityContextSchedulingTaskExecutor`]
* {security-api-url}org/springframework/security/task/DelegatingSecurityContextAsyncTaskExecutor.html[`DelegatingSecurityContextAsyncTaskExecutor`]
* {security-api-url}org/springframework/security/task/DelegatingSecurityContextTaskExecutor.html[`DelegatingSecurityContextTaskExecutor`]
* {security-api-url}org/springframework/security/scheduling/DelegatingSecurityContextTaskScheduler.html[`DelegatingSecurityContextTaskScheduler`]
