1 files changed, 63 insertions, 0 deletions
diff --git a/devtools/client/debugger/src/utils/context.js b/devtools/client/debugger/src/utils/context.js
new file mode 100644
index 0000000000..ef7fd23bb6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/context.js
@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getThreadContext } from "../selectors";
+
+// Context encapsulates the main parameters of the current redux state, which
+// impact most other information tracked by the debugger.
+//
+// The main use of Context is to control when asynchronous operations are
+// allowed to make changes to the program state. Such operations might be
+// invalidated as the state changes from the time the operation was originally
+// initiated. For example, operations on pause state might still continue even
+// after the thread unpauses.
+//
+// The methods below can be used to compare an old context with the current one
+// and see if the operation is now invalid and should be abandoned. Actions can
+// also include a 'cx' Context property, which will be checked by the context
+// middleware. If the action fails validateContextAction() then it will not be
+// dispatched.
+//
+// Context can additionally be used as a shortcut to access the main properties
+// of the pause state.
+
+// A normal Context is invalidated if the target navigates.
+
+// A ThreadContext is invalidated if the target navigates, or if the current
+// thread changes, pauses, or resumes.
+
+export class ContextError extends Error {}
+
+export function validateNavigateContext(state, cx) {
+  const newcx = getThreadContext(state);
+
+  if (newcx.navigateCounter != cx.navigateCounter) {
+    throw new ContextError("Page has navigated");
+  }
+}
+
+export function validateThreadContext(state, cx) {
+  const newcx = getThreadContext(state);
+
+  if (cx.thread != newcx.thread) {
+    throw new ContextError("Current thread has changed");
+  }
+
+  if (cx.pauseCounter != newcx.pauseCounter) {
+    throw new ContextError("Current thread has paused or resumed");
+  }
+}
+
+export function validateContext(state, cx) {
+  validateNavigateContext(state, cx);
+
+  if ("thread" in cx) {
+    validateThreadContext(state, cx);
+  }
+}
+
+export function isValidThreadContext(state, cx) {
+  const newcx = getThreadContext(state);
+  return cx.thread == newcx.thread && cx.pauseCounter == newcx.pauseCounter;
+}