jobqueue: Introduce jobqueue backed by a postgres database

Co-authored-by: sanne <sanne.raymaekers@gmail.com>

vendor/github.com/jackc/pgconn/internal/ctxwatch/context_watcher.go

@@ -0,0 +1,64 @@
+package ctxwatch
+
+import (
+	"context"
+)
+
+// ContextWatcher watches a context and performs an action when the context is canceled. It can watch one context at a
+// time.
+type ContextWatcher struct {
+	onCancel             func()
+	onUnwatchAfterCancel func()
+	unwatchChan          chan struct{}
+	watchInProgress      bool
+	onCancelWasCalled    bool
+}
+
+// NewContextWatcher returns a ContextWatcher. onCancel will be called when a watched context is canceled.
+// OnUnwatchAfterCancel will be called when Unwatch is called and the watched context had already been canceled and
+// onCancel called.
+func NewContextWatcher(onCancel func(), onUnwatchAfterCancel func()) *ContextWatcher {
+	cw := &ContextWatcher{
+		onCancel:             onCancel,
+		onUnwatchAfterCancel: onUnwatchAfterCancel,
+		unwatchChan:          make(chan struct{}),
+	}
+
+	return cw
+}
+
+// Watch starts watching ctx. If ctx is canceled then the onCancel function passed to NewContextWatcher will be called.
+func (cw *ContextWatcher) Watch(ctx context.Context) {
+	if cw.watchInProgress {
+		panic("Watch already in progress")
+	}
+
+	cw.onCancelWasCalled = false
+
+	if ctx.Done() != nil {
+		cw.watchInProgress = true
+		go func() {
+			select {
+			case <-ctx.Done():
+				cw.onCancel()
+				cw.onCancelWasCalled = true
+				<-cw.unwatchChan
+			case <-cw.unwatchChan:
+			}
+		}()
+	} else {
+		cw.watchInProgress = false
+	}
+}
+
+// Unwatch stops watching the previously watched context. If the onCancel function passed to NewContextWatcher was
+// called then onUnwatchAfterCancel will also be called.
+func (cw *ContextWatcher) Unwatch() {
+	if cw.watchInProgress {
+		cw.unwatchChan <- struct{}{}
+		if cw.onCancelWasCalled {
+			cw.onUnwatchAfterCancel()
+		}
+		cw.watchInProgress = false
+	}
+}