1 files changed, 136 insertions, 0 deletions
diff --git a/devtools/server/actors/resources/thread-states.js b/devtools/server/actors/resources/thread-states.js
new file mode 100644
index 0000000000..9ac79088d2
--- /dev/null
+++ b/devtools/server/actors/resources/thread-states.js
@@ -0,0 +1,136 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  TYPES: { THREAD_STATE },
+} = require("resource://devtools/server/actors/resources/index.js");
+
+const {
+  PAUSE_REASONS,
+  STATES: THREAD_STATES,
+} = require("resource://devtools/server/actors/thread.js");
+
+// Possible values of breakpoint's resource's `state` attribute
+const STATES = {
+  PAUSED: "paused",
+  RESUMED: "resumed",
+};
+
+/**
+ * Emit THREAD_STATE resources, which is emitted each time the target's thread pauses or resumes.
+ * So that there is two distinct values for this resource: pauses and resumes.
+ * These values are distinguished by `state` attribute which can be either "paused" or "resumed".
+ *
+ * Resume events, won't expose any other attribute other than `resourceType` and `state`.
+ *
+ * Pause events will expose the following attributes:
+ * - why {Object}: Description of why the thread pauses. See ThreadActor's PAUSE_REASONS definition for more information.
+ * - frame {Object}: Description of the frame where we just paused. This is a FrameActor's form.
+ */
+class BreakpointWatcher {
+  constructor() {
+    this.onPaused = this.onPaused.bind(this);
+    this.onResumed = this.onResumed.bind(this);
+  }
+
+  /**
+   * Start watching for state changes of the thread actor.
+   * This will notify whenever the thread actor pause and resume.
+   *
+   * @param TargetActor targetActor
+   *        The target actor from which we should observe breakpoints
+   * @param Object options
+   *        Dictionary object with following attributes:
+   *        - onAvailable: mandatory function
+   *          This will be called for each resource.
+   */
+  async watch(targetActor, { onAvailable }) {
+    const { threadActor } = targetActor;
+    this.threadActor = threadActor;
+    this.onAvailable = onAvailable;
+
+    // If this watcher is created during target creation, attach the thread actor automatically.
+    // Otherwise it would not pause on anything (especially debugger statements).
+    // However, do not attach the thread actor for Workers. They use a codepath
+    // which releases the worker on `attach`. For them, the client will call `attach`. (bug 1691986)
+    const isTargetCreation = this.threadActor.state == THREAD_STATES.DETACHED;
+    if (isTargetCreation && !targetActor.targetType.endsWith("worker")) {
+      await this.threadActor.attach({});
+    }
+
+    this.isInterrupted = false;
+
+    threadActor.on("paused", this.onPaused);
+    threadActor.on("resumed", this.onResumed);
+
+    // For top-level targets, the thread actor may have been attached by the frontend
+    // on toolbox opening, and we start observing for thread state updates much later.
+    // In which case, the thread actor may already be paused and we handle this here.
+    // It will also occurs for all other targets once bug 1681698 lands,
+    // as the thread actor will be initialized before the target starts loading.
+    // And it will occur for all targets once bug 1686748 lands.
+    //
+    // Note that we have to check if we have a "lastPausedPacket",
+    // because the thread Actor is immediately set as being paused,
+    // but the pause packet is built asynchronously and available slightly later.
+    // If the "lastPausedPacket" is null, while the thread actor is paused,
+    // it is fine to ignore as the "paused" event will be fire later.
+    if (threadActor.isPaused() && threadActor.lastPausedPacket()) {
+      this.onPaused(threadActor.lastPausedPacket());
+    }
+  }
+
+  /**
+   * Stop watching for breakpoints
+   */
+  destroy() {
+    this.threadActor.off("paused", this.onPaused);
+    this.threadActor.off("resumed", this.onResumed);
+  }
+
+  onPaused(packet) {
+    // If paused by an explicit interrupt, which are generated by the
+    // slow script dialog and internal events such as setting
+    // breakpoints, ignore the event.
+    const { why } = packet;
+    if (why.type === PAUSE_REASONS.INTERRUPTED && !why.onNext) {
+      this.isInterrupted = true;
+      return;
+    }
+
+    // Ignore attached events because they are not useful to the user.
+    if (why.type == PAUSE_REASONS.ALREADY_PAUSED) {
+      return;
+    }
+
+    this.onAvailable([
+      {
+        resourceType: THREAD_STATE,
+        state: STATES.PAUSED,
+        why,
+        frame: packet.frame.form(),
+      },
+    ]);
+  }
+
+  onResumed(packet) {
+    // NOTE: resumed events are suppressed while interrupted
+    // to prevent unintentional behavior.
+    if (this.isInterrupted) {
+      this.isInterrupted = false;
+      return;
+    }
+
+    this.onAvailable([
+      {
+        resourceType: THREAD_STATE,
+        state: STATES.RESUMED,
+      },
+    ]);
+  }
+}
+
+module.exports = BreakpointWatcher;