// Running under TSAN, this fails with "signal handler
// spoils errno".

/*
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>

void go_callback();

static void *thr(void *arg) {
	int i;
	for (i = 0; i < 10; i++)
		go_callback();
	return 0;
}

static void *sendthr(void *arg) {
	pthread_t th = *(pthread_t*)arg;
	while (1) {
		int r = pthread_kill(th, SIGWINCH);
		if (r < 0)

    MockCallback callback = new MockCallback("foo");
    addCallback(f, callback, directExecutor());
    f.set("foo");
  }

  public void testExecutorSuccess() {
    CountingSameThreadExecutor ex = new CountingSameThreadExecutor();
    SettableFuture<String> f = SettableFuture.create();
    MockCallback callback = new MockCallback("foo");
    Futures.addCallback(f, callback, ex);
    f.set("foo");

	"runtime"
	"unsafe"
)

var callback func()

//go:noinline
//go:uintptrescapes
func F(ptr uintptr) { callback() }

//go:noinline
//go:uintptrescapes
func Fv(ptrs ...uintptr) { callback() }

type T struct{}

//go:noinline
//go:uintptrescapes
func (T) M(ptr uintptr) { callback() }

//go:noinline
//go:uintptrescapes
func (T) Mv(ptrs ...uintptr) { callback() }

    boolean isCancellationRequested();

    /**
     * Adds a callback that will be executed when cancel event is triggered.
     * It can be run synchronously if the token is already cancelled.
     *
     * @param cancellationHandler callback to be executed when cancel is requested.
     * @return current state of cancellation request before callback was added.
     */
    boolean addCallback(Runnable cancellationHandler);

    MockCallback callback = new MockCallback("foo");
    addCallback(f, callback, directExecutor());
    f.set("foo");
  }

  public void testExecutorSuccess() {
    CountingSameThreadExecutor ex = new CountingSameThreadExecutor();
    SettableFuture<String> f = SettableFuture.create();
    MockCallback callback = new MockCallback("foo");
    Futures.addCallback(f, callback, ex);
    f.set("foo");

        if (queryLambda != null) {
            queryLambda.callback(cq);
        }
        FilterAggregationBuilder builder = regFilterA(name, cq.getQuery());
        if (opLambda != null) {
            opLambda.callback(builder);
        }
        if (aggsLambda != null) {
            RoleCA ca = new RoleCA();
            aggsLambda.callback(ca);
            ca.getAggregationBuilderList().forEach(builder::subAggregation);

// _cgo_getstackbound, then writes to the same G can be seen on multiple
// threads (when the G is reused after thread exit). This would trigger TSAN.

/*
#include <pthread.h>

void go_callback();

static void *thr(void *arg) {
    go_callback();
    return 0;
}

static void foo() {
    pthread_t th;
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setstacksize(&attr, 256 << 10);

            Consumer<RESPONSE> callback;
            while ((callback = doneCallbacks.poll()) != null) {
                executeCallbacks.add(callback);
            }
        }
        if (executeCallbacks.size() > 0) {
            try {
                executeCallbacks.stream().forEach(callback -> callback.accept(response));
            } catch (final Exception ignore) {}
        }

    }

    def 'removed callback is not notified'() {
        def token = new DefaultBuildCancellationToken()

        def callback = Mock(Runnable)
        token.addCallback(callback)
        token.removeCallback(callback)

        when:
        token.cancel()

        then:
        token.cancellationRequested
        0 * callback.run()
    }

## Die normale **FastAPI**-Anwendung

Sehen wir uns zunächst an, wie die normale API-Anwendung aussehen würde, bevor wir den Callback hinzufügen.

Sie verfügt über eine *Pfadoperation*, die einen `Invoice`-Body empfängt, und einen Query-Parameter `callback_url`, der die URL für den Callback enthält.