Add m-esr52 at 52.6.0

13 files changed, 1569 insertions, 0 deletions

diff --git a/devtools/client/memory/actions/allocations.js b/devtools/client/memory/actions/allocations.js
new file mode 100644
index 000000000..521319925
--- /dev/null
+++ b/devtools/client/memory/actions/allocations.js
@@ -0,0 +1,20 @@
+/* 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 { actions, ALLOCATION_RECORDING_OPTIONS } = require("../constants");
+
+exports.toggleRecordingAllocationStacks = function (front) {
+  return function* (dispatch, getState) {
+    dispatch({ type: actions.TOGGLE_RECORD_ALLOCATION_STACKS_START });
+
+    if (getState().recordingAllocationStacks) {
+      yield front.stopRecordingAllocations();
+    } else {
+      yield front.startRecordingAllocations(ALLOCATION_RECORDING_OPTIONS);
+    }
+
+    dispatch({ type: actions.TOGGLE_RECORD_ALLOCATION_STACKS_END });
+  };
+};
diff --git a/devtools/client/memory/actions/census-display.js b/devtools/client/memory/actions/census-display.js
new file mode 100644
index 000000000..348a8951a
--- /dev/null
+++ b/devtools/client/memory/actions/census-display.js
@@ -0,0 +1,34 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+const { actions } = require("../constants");
+const { refresh } = require("./refresh");
+
+exports.setCensusDisplayAndRefresh = function (heapWorker, display) {
+  return function* (dispatch, getState) {
+    dispatch(setCensusDisplay(display));
+    yield dispatch(refresh(heapWorker));
+  };
+};
+
+/**
+ * Clears out all cached census data in the snapshots and sets new display data
+ * for censuses.
+ *
+ * @param {censusDisplayModel} display
+ */
+const setCensusDisplay = exports.setCensusDisplay = function (display) {
+  assert(typeof display === "object"
+         && display
+         && display.breakdown
+         && display.breakdown.by,
+    `Breakdowns must be an object with a \`by\` property, attempted to set: ${uneval(display)}`);
+
+  return {
+    type: actions.SET_CENSUS_DISPLAY,
+    display,
+  };
+};
diff --git a/devtools/client/memory/actions/diffing.js b/devtools/client/memory/actions/diffing.js
new file mode 100644
index 000000000..70af307bb
--- /dev/null
+++ b/devtools/client/memory/actions/diffing.js
@@ -0,0 +1,201 @@
+/* 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 { assert, reportException } = require("devtools/shared/DevToolsUtils");
+const { actions, diffingState, viewState } = require("../constants");
+const telemetry = require("../telemetry");
+const {
+  getSnapshot,
+  censusIsUpToDate,
+  snapshotIsDiffable,
+  findSelectedSnapshot,
+} = require("../utils");
+// This is a circular dependency, so do not destructure the needed properties.
+const snapshotActions = require("./snapshot");
+
+/**
+ * Toggle diffing mode on or off.
+ */
+const toggleDiffing = exports.toggleDiffing = function () {
+  return function (dispatch, getState) {
+    dispatch({
+      type: actions.CHANGE_VIEW,
+      newViewState: getState().diffing ? viewState.CENSUS : viewState.DIFFING,
+      oldDiffing: getState().diffing,
+      oldSelected: findSelectedSnapshot(getState()),
+    });
+  };
+};
+
+/**
+ * Select the given snapshot for diffing.
+ *
+ * @param {snapshotModel} snapshot
+ */
+const selectSnapshotForDiffing = exports.selectSnapshotForDiffing = function (snapshot) {
+  assert(snapshotIsDiffable(snapshot),
+         "To select a snapshot for diffing, it must be diffable");
+  return { type: actions.SELECT_SNAPSHOT_FOR_DIFFING, snapshot };
+};
+
+/**
+ * Compute the difference between the first and second snapshots.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotModel} first
+ * @param {snapshotModel} second
+ */
+const takeCensusDiff = exports.takeCensusDiff = function (heapWorker, first, second) {
+  return function* (dispatch, getState) {
+    assert(snapshotIsDiffable(first),
+           `First snapshot must be in a diffable state, found ${first.state}`);
+    assert(snapshotIsDiffable(second),
+           `Second snapshot must be in a diffable state, found ${second.state}`);
+
+    let report, parentMap;
+    let display = getState().censusDisplay;
+    let filter = getState().filter;
+
+    if (censusIsUpToDate(filter, display, getState().diffing.census)) {
+      return;
+    }
+
+    do {
+      if (!getState().diffing
+          || getState().diffing.firstSnapshotId !== first.id
+          || getState().diffing.secondSnapshotId !== second.id) {
+        // If we stopped diffing or stopped and then started diffing a different
+        // pair of snapshots, then just give up with diffing this pair. In the
+        // latter case, a newly spawned task will handle the diffing for the new
+        // pair.
+        return;
+      }
+
+      display = getState().censusDisplay;
+      filter = getState().filter;
+
+      dispatch({
+        type: actions.TAKE_CENSUS_DIFF_START,
+        first,
+        second,
+        filter,
+        display,
+      });
+
+      let opts = display.inverted
+        ? { asInvertedTreeNode: true }
+        : { asTreeNode: true };
+      opts.filter = filter || null;
+
+      try {
+        ({ delta: report, parentMap } = yield heapWorker.takeCensusDiff(
+          first.path,
+          second.path,
+          { breakdown: display.breakdown },
+          opts));
+      } catch (error) {
+        reportException("actions/diffing/takeCensusDiff", error);
+        dispatch({ type: actions.DIFFING_ERROR, error });
+        return;
+      }
+    }
+    while (filter !== getState().filter
+           || display !== getState().censusDisplay);
+
+    dispatch({
+      type: actions.TAKE_CENSUS_DIFF_END,
+      first,
+      second,
+      report,
+      parentMap,
+      filter,
+      display,
+    });
+
+    telemetry.countDiff({ filter, display });
+  };
+};
+
+/**
+ * Ensure that the current diffing data is up to date with the currently
+ * selected display, filter, etc. If the state is not up-to-date, then a
+ * recompute is triggered.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const refreshDiffing = exports.refreshDiffing = function (heapWorker) {
+  return function* (dispatch, getState) {
+    if (getState().diffing.secondSnapshotId === null) {
+      return;
+    }
+
+    assert(getState().diffing.firstSnapshotId,
+           "Should have first snapshot id");
+
+    if (getState().diffing.state === diffingState.TAKING_DIFF) {
+      // There is an existing task that will ensure that the diffing data is
+      // up-to-date.
+      return;
+    }
+
+    const { firstSnapshotId, secondSnapshotId } = getState().diffing;
+
+    const first = getSnapshot(getState(), firstSnapshotId);
+    const second = getSnapshot(getState(), secondSnapshotId);
+    dispatch(takeCensusDiff(heapWorker, first, second));
+  };
+};
+
+/**
+ * Select the given snapshot for diffing and refresh the diffing data if
+ * necessary (for example, if two snapshots are now selected for diffing).
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotModel} snapshot
+ */
+const selectSnapshotForDiffingAndRefresh = exports.selectSnapshotForDiffingAndRefresh = function (heapWorker, snapshot) {
+  return function* (dispatch, getState) {
+    assert(getState().diffing,
+           "If we are selecting for diffing, we must be in diffing mode");
+    dispatch(selectSnapshotForDiffing(snapshot));
+    yield dispatch(refreshDiffing(heapWorker));
+  };
+};
+
+/**
+ * Expand the given node in the diffing's census's delta-report.
+ *
+ * @param {CensusTreeNode} node
+ */
+const expandDiffingCensusNode = exports.expandDiffingCensusNode = function (node) {
+  return {
+    type: actions.EXPAND_DIFFING_CENSUS_NODE,
+    node,
+  };
+};
+
+/**
+ * Collapse the given node in the diffing's census's delta-report.
+ *
+ * @param {CensusTreeNode} node
+ */
+const collapseDiffingCensusNode = exports.collapseDiffingCensusNode = function (node) {
+  return {
+    type: actions.COLLAPSE_DIFFING_CENSUS_NODE,
+    node,
+  };
+};
+
+/**
+ * Focus the given node in the snapshot's census's report.
+ *
+ * @param {DominatorTreeNode} node
+ */
+const focusDiffingCensusNode = exports.focusDiffingCensusNode = function (node) {
+  return {
+    type: actions.FOCUS_DIFFING_CENSUS_NODE,
+    node,
+  };
+};
diff --git a/devtools/client/memory/actions/filter.js b/devtools/client/memory/actions/filter.js
new file mode 100644
index 000000000..c578b037a
--- /dev/null
+++ b/devtools/client/memory/actions/filter.js
@@ -0,0 +1,35 @@
+/* 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 { actions } = require("../constants");
+const { refresh } = require("./refresh");
+
+const setFilterString = exports.setFilterString = function (filterString) {
+  return {
+    type: actions.SET_FILTER_STRING,
+    filter: filterString
+  };
+};
+
+// The number of milliseconds we should wait before kicking off a new census
+// when the filter string is updated. This helps us avoid doing any work while
+// the user is still typing.
+const FILTER_INPUT_DEBOUNCE_MS = 250;
+
+// The timer id for the debounced census refresh.
+let timerId = null;
+
+exports.setFilterStringAndRefresh = function (filterString, heapWorker) {
+  return function* (dispatch, getState) {
+    dispatch(setFilterString(filterString));
+
+    if (timerId !== null) {
+      clearTimeout(timerId);
+    }
+
+    timerId = setTimeout(() => dispatch(refresh(heapWorker)),
+                         FILTER_INPUT_DEBOUNCE_MS);
+  };
+};
diff --git a/devtools/client/memory/actions/io.js b/devtools/client/memory/actions/io.js
new file mode 100644
index 000000000..10b45aee5
--- /dev/null
+++ b/devtools/client/memory/actions/io.js
@@ -0,0 +1,97 @@
+/* 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 { immutableUpdate, reportException, assert } = require("devtools/shared/DevToolsUtils");
+const { snapshotState: states, actions, viewState } = require("../constants");
+const { L10N, openFilePicker, createSnapshot } = require("../utils");
+const telemetry = require("../telemetry");
+const { OS } = require("resource://gre/modules/osfile.jsm");
+const {
+  selectSnapshot,
+  computeSnapshotData,
+  readSnapshot,
+  takeCensus,
+  takeTreeMap
+} = require("./snapshot");
+const VALID_EXPORT_STATES = [states.SAVED, states.READ];
+
+exports.pickFileAndExportSnapshot = function (snapshot) {
+  return function* (dispatch, getState) {
+    let outputFile = yield openFilePicker({
+      title: L10N.getFormatStr("snapshot.io.save.window"),
+      defaultName: OS.Path.basename(snapshot.path),
+      filters: [[L10N.getFormatStr("snapshot.io.filter"), "*.fxsnapshot"]],
+      mode: "save",
+    });
+
+    if (!outputFile) {
+      return;
+    }
+
+    yield dispatch(exportSnapshot(snapshot, outputFile.path));
+  };
+};
+
+const exportSnapshot = exports.exportSnapshot = function (snapshot, dest) {
+  return function* (dispatch, getState) {
+    telemetry.countExportSnapshot();
+
+    dispatch({ type: actions.EXPORT_SNAPSHOT_START, snapshot });
+
+    assert(VALID_EXPORT_STATES.includes(snapshot.state),
+      `Snapshot is in invalid state for exporting: ${snapshot.state}`);
+
+    try {
+      yield OS.File.copy(snapshot.path, dest);
+    } catch (error) {
+      reportException("exportSnapshot", error);
+      dispatch({ type: actions.EXPORT_SNAPSHOT_ERROR, snapshot, error });
+    }
+
+    dispatch({ type: actions.EXPORT_SNAPSHOT_END, snapshot });
+  };
+};
+
+const pickFileAndImportSnapshotAndCensus = exports.pickFileAndImportSnapshotAndCensus = function (heapWorker) {
+  return function* (dispatch, getState) {
+    let input = yield openFilePicker({
+      title: L10N.getFormatStr("snapshot.io.import.window"),
+      filters: [[L10N.getFormatStr("snapshot.io.filter"), "*.fxsnapshot"]],
+      mode: "open",
+    });
+
+    if (!input) {
+      return;
+    }
+
+    yield dispatch(importSnapshotAndCensus(heapWorker, input.path));
+  };
+};
+
+const importSnapshotAndCensus = exports.importSnapshotAndCensus = function (heapWorker, path) {
+  return function* (dispatch, getState) {
+    telemetry.countImportSnapshot();
+
+    const snapshot = immutableUpdate(createSnapshot(getState()), {
+      path,
+      state: states.IMPORTING,
+      imported: true,
+    });
+    const id = snapshot.id;
+
+    dispatch({ type: actions.IMPORT_SNAPSHOT_START, snapshot });
+    dispatch(selectSnapshot(snapshot.id));
+
+    try {
+      yield dispatch(readSnapshot(heapWorker, id));
+      yield dispatch(computeSnapshotData(heapWorker, id));
+    } catch (error) {
+      reportException("importSnapshot", error);
+      dispatch({ type: actions.IMPORT_SNAPSHOT_ERROR, error, id });
+    }
+
+    dispatch({ type: actions.IMPORT_SNAPSHOT_END, id });
+  };
+};
diff --git a/devtools/client/memory/actions/label-display.js b/devtools/client/memory/actions/label-display.js
new file mode 100644
index 000000000..6e68293ab
--- /dev/null
+++ b/devtools/client/memory/actions/label-display.js
@@ -0,0 +1,38 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+const { actions } = require("../constants");
+const { refresh } = require("./refresh");
+
+/**
+ * Change the display we use for labeling individual nodes and refresh the
+ * current data.
+ */
+exports.setLabelDisplayAndRefresh = function (heapWorker, display) {
+  return function* (dispatch, getState) {
+    // Clears out all stored census data and sets the display.
+    dispatch(setLabelDisplay(display));
+    yield dispatch(refresh(heapWorker));
+  };
+};
+
+/**
+ * Change the display we use for labeling individual nodes.
+ *
+ * @param {labelDisplayModel} display
+ */
+const setLabelDisplay = exports.setLabelDisplay = function (display) {
+  assert(typeof display === "object"
+         && display
+         && display.breakdown
+         && display.breakdown.by,
+    `Breakdowns must be an object with a \`by\` property, attempted to set: ${uneval(display)}`);
+
+  return {
+    type: actions.SET_LABEL_DISPLAY,
+    display,
+  };
+};
diff --git a/devtools/client/memory/actions/moz.build b/devtools/client/memory/actions/moz.build
new file mode 100644
index 000000000..8b26aff9f
--- /dev/null
+++ b/devtools/client/memory/actions/moz.build
@@ -0,0 +1,19 @@
+# vim: set filetype=python:
+# 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/.
+
+DevToolsModules(
+    'allocations.js',
+    'census-display.js',
+    'diffing.js',
+    'filter.js',
+    'io.js',
+    'label-display.js',
+    'refresh.js',
+    'sizes.js',
+    'snapshot.js',
+    'task-cache.js',
+    'tree-map-display.js',
+    'view.js',
+)
diff --git a/devtools/client/memory/actions/refresh.js b/devtools/client/memory/actions/refresh.js
new file mode 100644
index 000000000..801a4f867
--- /dev/null
+++ b/devtools/client/memory/actions/refresh.js
@@ -0,0 +1,44 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+const { viewState } = require("../constants");
+const { refreshDiffing } = require("./diffing");
+const snapshot = require("./snapshot");
+
+/**
+ * Refresh the main thread's data from the heap analyses worker, if needed.
+ *
+ * @param {HeapAnalysesWorker} heapWorker
+ */
+exports.refresh = function (heapWorker) {
+  return function* (dispatch, getState) {
+    switch (getState().view.state) {
+      case viewState.DIFFING:
+        assert(getState().diffing, "Should have diffing state if in diffing view");
+        yield dispatch(refreshDiffing(heapWorker));
+        return;
+
+      case viewState.CENSUS:
+        yield dispatch(snapshot.refreshSelectedCensus(heapWorker));
+        return;
+
+      case viewState.DOMINATOR_TREE:
+        yield dispatch(snapshot.refreshSelectedDominatorTree(heapWorker));
+        return;
+
+      case viewState.TREE_MAP:
+        yield dispatch(snapshot.refreshSelectedTreeMap(heapWorker));
+        return;
+
+      case viewState.INDIVIDUALS:
+        yield dispatch(snapshot.refreshIndividuals(heapWorker));
+        return;
+
+      default:
+        assert(false, `Unexpected view state: ${getState().view.state}`);
+    }
+  };
+};
diff --git a/devtools/client/memory/actions/sizes.js b/devtools/client/memory/actions/sizes.js
new file mode 100644
index 000000000..7239803e7
--- /dev/null
+++ b/devtools/client/memory/actions/sizes.js
@@ -0,0 +1,13 @@
+/* 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 { actions } = require("../constants");
+
+exports.resizeShortestPaths = function (newSize) {
+  return {
+    type: actions.RESIZE_SHORTEST_PATHS,
+    size: newSize,
+  };
+};
diff --git a/devtools/client/memory/actions/snapshot.js b/devtools/client/memory/actions/snapshot.js
new file mode 100644
index 000000000..adb24977e
--- /dev/null
+++ b/devtools/client/memory/actions/snapshot.js
@@ -0,0 +1,865 @@
+/* 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 { Preferences } = require("resource://gre/modules/Preferences.jsm");
+const { assert, reportException, isSet } = require("devtools/shared/DevToolsUtils");
+const {
+  censusIsUpToDate,
+  getSnapshot,
+  createSnapshot,
+  dominatorTreeIsComputed,
+} = require("../utils");
+const {
+  actions,
+  snapshotState: states,
+  viewState,
+  censusState,
+  treeMapState,
+  dominatorTreeState,
+  individualsState,
+} = require("../constants");
+const telemetry = require("../telemetry");
+const view = require("./view");
+const refresh = require("./refresh");
+const diffing = require("./diffing");
+const TaskCache = require("./task-cache");
+
+/**
+ * A series of actions are fired from this task to save, read and generate the
+ * initial census from a snapshot.
+ *
+ * @param {MemoryFront}
+ * @param {HeapAnalysesClient}
+ * @param {Object}
+ */
+const takeSnapshotAndCensus = exports.takeSnapshotAndCensus = function (front, heapWorker) {
+  return function* (dispatch, getState) {
+    const id = yield dispatch(takeSnapshot(front));
+    if (id === null) {
+      return;
+    }
+
+    yield dispatch(readSnapshot(heapWorker, id));
+    if (getSnapshot(getState(), id).state !== states.READ) {
+      return;
+    }
+
+    yield dispatch(computeSnapshotData(heapWorker, id));
+  };
+};
+
+/**
+ * Create the census for the snapshot with the provided snapshot id. If the
+ * current view is the DOMINATOR_TREE view, create the dominator tree for this
+ * snapshot as well.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotId} id
+ */
+const computeSnapshotData = exports.computeSnapshotData = function (heapWorker, id) {
+  return function* (dispatch, getState) {
+    if (getSnapshot(getState(), id).state !== states.READ) {
+      return;
+    }
+
+    // Decide which type of census to take.
+    const censusTaker = getCurrentCensusTaker(getState().view.state);
+    yield dispatch(censusTaker(heapWorker, id));
+
+    if (getState().view.state === viewState.DOMINATOR_TREE &&
+        !getSnapshot(getState(), id).dominatorTree) {
+      yield dispatch(computeAndFetchDominatorTree(heapWorker, id));
+    }
+  };
+};
+
+/**
+ * Selects a snapshot and if the snapshot's census is using a different
+ * display, take a new census.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotId} id
+ */
+const selectSnapshotAndRefresh = exports.selectSnapshotAndRefresh = function (heapWorker, id) {
+  return function* (dispatch, getState) {
+    if (getState().diffing || getState().individuals) {
+      dispatch(view.changeView(viewState.CENSUS));
+    }
+
+    dispatch(selectSnapshot(id));
+    yield dispatch(refresh.refresh(heapWorker));
+  };
+};
+
+/**
+ * Take a snapshot and return its id on success, or null on failure.
+ *
+ * @param {MemoryFront} front
+ * @returns {Number|null}
+ */
+const takeSnapshot = exports.takeSnapshot = function (front) {
+  return function* (dispatch, getState) {
+    telemetry.countTakeSnapshot();
+
+    if (getState().diffing || getState().individuals) {
+      dispatch(view.changeView(viewState.CENSUS));
+    }
+
+    const snapshot = createSnapshot(getState());
+    const id = snapshot.id;
+    dispatch({ type: actions.TAKE_SNAPSHOT_START, snapshot });
+    dispatch(selectSnapshot(id));
+
+    let path;
+    try {
+      path = yield front.saveHeapSnapshot();
+    } catch (error) {
+      reportException("takeSnapshot", error);
+      dispatch({ type: actions.SNAPSHOT_ERROR, id, error });
+      return null;
+    }
+
+    dispatch({ type: actions.TAKE_SNAPSHOT_END, id, path });
+    return snapshot.id;
+  };
+};
+
+/**
+ * Reads a snapshot into memory; necessary to do before taking
+ * a census on the snapshot. May only be called once per snapshot.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotId} id
+ */
+const readSnapshot = exports.readSnapshot =
+TaskCache.declareCacheableTask({
+  getCacheKey(_, id) {
+    return id;
+  },
+
+  task: function* (heapWorker, id, removeFromCache, dispatch, getState) {
+    const snapshot = getSnapshot(getState(), id);
+    assert([states.SAVED, states.IMPORTING].includes(snapshot.state),
+           `Should only read a snapshot once. Found snapshot in state ${snapshot.state}`);
+
+    let creationTime;
+
+    dispatch({ type: actions.READ_SNAPSHOT_START, id });
+    try {
+      yield heapWorker.readHeapSnapshot(snapshot.path);
+      creationTime = yield heapWorker.getCreationTime(snapshot.path);
+    } catch (error) {
+      removeFromCache();
+      reportException("readSnapshot", error);
+      dispatch({ type: actions.SNAPSHOT_ERROR, id, error });
+      return;
+    }
+
+    removeFromCache();
+    dispatch({ type: actions.READ_SNAPSHOT_END, id, creationTime });
+  }
+});
+
+let takeCensusTaskCounter = 0;
+
+/**
+ * Census and tree maps both require snapshots. This function shares the logic
+ * of creating snapshots, but is configurable with specific actions for the
+ * individual census types.
+ *
+ * @param {getDisplay} Get the display object from the state.
+ * @param {getCensus} Get the census from the snapshot.
+ * @param {beginAction} Action to send at the beginning of a heap snapshot.
+ * @param {endAction} Action to send at the end of a heap snapshot.
+ * @param {errorAction} Action to send if a snapshot has an error.
+ */
+function makeTakeCensusTask({ getDisplay, getFilter, getCensus, beginAction,
+                              endAction, errorAction, canTakeCensus }) {
+  /**
+   * @param {HeapAnalysesClient} heapWorker
+   * @param {snapshotId} id
+   *
+   * @see {Snapshot} model defined in devtools/client/memory/models.js
+   * @see `devtools/shared/heapsnapshot/HeapAnalysesClient.js`
+   * @see `js/src/doc/Debugger/Debugger.Memory.md` for breakdown details
+   */
+  let thisTakeCensusTaskId = ++takeCensusTaskCounter;
+  return TaskCache.declareCacheableTask({
+    getCacheKey(_, id) {
+      return `take-census-task-${thisTakeCensusTaskId}-${id}`;
+    },
+
+    task: function* (heapWorker, id, removeFromCache, dispatch, getState) {
+      const snapshot = getSnapshot(getState(), id);
+      if (!snapshot) {
+        removeFromCache();
+        return;
+      }
+
+      // Assert that snapshot is in a valid state
+      assert(canTakeCensus(snapshot),
+             `Attempting to take a census when the snapshot is not in a ready state. snapshot.state = ${snapshot.state}, census.state = ${(getCensus(snapshot) || { state: null }).state}`);
+
+      let report, parentMap;
+      let display = getDisplay(getState());
+      let filter = getFilter(getState());
+
+      // If display, filter and inversion haven't changed, don't do anything.
+      if (censusIsUpToDate(filter, display, getCensus(snapshot))) {
+        removeFromCache();
+        return;
+      }
+
+      // Keep taking a census if the display changes while our request is in
+      // flight. Recheck that the display used for the census is the same as the
+      // state's display.
+      do {
+        display = getDisplay(getState());
+        filter = getState().filter;
+
+        dispatch({
+          type: beginAction,
+          id,
+          filter,
+          display
+        });
+
+        let opts = display.inverted
+          ? { asInvertedTreeNode: true }
+          : { asTreeNode: true };
+
+        opts.filter = filter || null;
+
+        try {
+          ({ report, parentMap } = yield heapWorker.takeCensus(
+            snapshot.path,
+            { breakdown: display.breakdown },
+            opts));
+        } catch (error) {
+          removeFromCache();
+          reportException("takeCensus", error);
+          dispatch({ type: errorAction, id, error });
+          return;
+        }
+      }
+      while (filter !== getState().filter ||
+             display !== getDisplay(getState()));
+
+      removeFromCache();
+      dispatch({
+        type: endAction,
+        id,
+        display,
+        filter,
+        report,
+        parentMap
+      });
+
+      telemetry.countCensus({ filter, display });
+    }
+  });
+}
+
+/**
+ * Take a census.
+ */
+const takeCensus = exports.takeCensus = makeTakeCensusTask({
+  getDisplay: (state) => state.censusDisplay,
+  getFilter: (state) => state.filter,
+  getCensus: (snapshot) => snapshot.census,
+  beginAction: actions.TAKE_CENSUS_START,
+  endAction: actions.TAKE_CENSUS_END,
+  errorAction: actions.TAKE_CENSUS_ERROR,
+  canTakeCensus: snapshot =>
+    snapshot.state === states.READ &&
+    (!snapshot.census || snapshot.census.state === censusState.SAVED),
+});
+
+/**
+ * Take a census for the treemap.
+ */
+const takeTreeMap = exports.takeTreeMap = makeTakeCensusTask({
+  getDisplay: (state) => state.treeMapDisplay,
+  getFilter: () => null,
+  getCensus: (snapshot) => snapshot.treeMap,
+  beginAction: actions.TAKE_TREE_MAP_START,
+  endAction: actions.TAKE_TREE_MAP_END,
+  errorAction: actions.TAKE_TREE_MAP_ERROR,
+  canTakeCensus: snapshot =>
+    snapshot.state === states.READ &&
+    (!snapshot.treeMap || snapshot.treeMap.state === treeMapState.SAVED),
+});
+
+/**
+ * Define what should be the default mode for taking a census based on the
+ * default view of the tool.
+ */
+const defaultCensusTaker = takeTreeMap;
+
+/**
+ * Pick the default census taker when taking a snapshot. This should be
+ * determined by the current view. If the view doesn't include a census, then
+ * use the default one defined above. Some census information is always needed
+ * to display some basic information about a snapshot.
+ *
+ * @param {string} value from viewState
+ */
+const getCurrentCensusTaker = exports.getCurrentCensusTaker = function (currentView) {
+  switch (currentView) {
+    case viewState.TREE_MAP:
+      return takeTreeMap;
+    case viewState.CENSUS:
+      return takeCensus;
+    default:
+      return defaultCensusTaker;
+  }
+};
+
+/**
+ * Focus the given node in the individuals view.
+ *
+ * @param {DominatorTreeNode} node.
+ */
+const focusIndividual = exports.focusIndividual = function (node) {
+  return {
+    type: actions.FOCUS_INDIVIDUAL,
+    node,
+  };
+};
+
+/**
+ * Fetch the individual `DominatorTreeNodes` for the census group specified by
+ * `censusBreakdown` and `reportLeafIndex`.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {SnapshotId} id
+ * @param {Object} censusBreakdown
+ * @param {Set<Number> | Number} reportLeafIndex
+ */
+const fetchIndividuals = exports.fetchIndividuals =
+function (heapWorker, id, censusBreakdown, reportLeafIndex) {
+  return function* (dispatch, getState) {
+    if (getState().view.state !== viewState.INDIVIDUALS) {
+      dispatch(view.changeView(viewState.INDIVIDUALS));
+    }
+
+    const snapshot = getSnapshot(getState(), id);
+    assert(snapshot && snapshot.state === states.READ,
+           "The snapshot should already be read into memory");
+
+    if (!dominatorTreeIsComputed(snapshot)) {
+      yield dispatch(computeAndFetchDominatorTree(heapWorker, id));
+    }
+
+    const snapshot_ = getSnapshot(getState(), id);
+    assert(snapshot_.dominatorTree && snapshot_.dominatorTree.root,
+           "Should have a dominator tree with a root.");
+
+    const dominatorTreeId = snapshot_.dominatorTree.dominatorTreeId;
+
+    const indices = isSet(reportLeafIndex)
+      ? reportLeafIndex
+      : new Set([reportLeafIndex]);
+
+    let labelDisplay;
+    let nodes;
+    do {
+      labelDisplay = getState().labelDisplay;
+      assert(labelDisplay && labelDisplay.breakdown && labelDisplay.breakdown.by,
+             `Should have a breakdown to label nodes with, got: ${uneval(labelDisplay)}`);
+
+      if (getState().view.state !== viewState.INDIVIDUALS) {
+        // We switched views while in the process of fetching individuals -- any
+        // further work is useless.
+        return;
+      }
+
+      dispatch({ type: actions.FETCH_INDIVIDUALS_START });
+
+      try {
+        ({ nodes } = yield heapWorker.getCensusIndividuals({
+          dominatorTreeId,
+          indices,
+          censusBreakdown,
+          labelBreakdown: labelDisplay.breakdown,
+          maxRetainingPaths: Preferences.get("devtools.memory.max-retaining-paths"),
+          maxIndividuals: Preferences.get("devtools.memory.max-individuals"),
+        }));
+      } catch (error) {
+        reportException("actions/snapshot/fetchIndividuals", error);
+        dispatch({ type: actions.INDIVIDUALS_ERROR, error });
+        return;
+      }
+    }
+    while (labelDisplay !== getState().labelDisplay);
+
+    dispatch({
+      type: actions.FETCH_INDIVIDUALS_END,
+      id,
+      censusBreakdown,
+      indices,
+      labelDisplay,
+      nodes,
+      dominatorTree: snapshot_.dominatorTree,
+    });
+  };
+};
+
+/**
+ * Refresh the current individuals view.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const refreshIndividuals = exports.refreshIndividuals = function (heapWorker) {
+  return function* (dispatch, getState) {
+    assert(getState().view.state === viewState.INDIVIDUALS,
+           "Should be in INDIVIDUALS view.");
+
+    const { individuals } = getState();
+
+    switch (individuals.state) {
+      case individualsState.COMPUTING_DOMINATOR_TREE:
+      case individualsState.FETCHING:
+        // Nothing to do here.
+        return;
+
+      case individualsState.FETCHED:
+        if (getState().individuals.labelDisplay === getState().labelDisplay) {
+          return;
+        }
+        break;
+
+      case individualsState.ERROR:
+        // Doesn't hurt to retry: maybe we won't get an error this time around?
+        break;
+
+      default:
+        assert(false, `Unexpected individuals state: ${individuals.state}`);
+        return;
+    }
+
+    yield dispatch(fetchIndividuals(heapWorker,
+                                    individuals.id,
+                                    individuals.censusBreakdown,
+                                    individuals.indices));
+  };
+};
+
+/**
+ * Refresh the selected snapshot's census data, if need be (for example,
+ * display configuration changed).
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const refreshSelectedCensus = exports.refreshSelectedCensus = function (heapWorker) {
+  return function* (dispatch, getState) {
+    let snapshot = getState().snapshots.find(s => s.selected);
+    if (!snapshot || snapshot.state !== states.READ) {
+      return;
+    }
+
+    // Intermediate snapshot states will get handled by the task action that is
+    // orchestrating them. For example, if the snapshot census's state is
+    // SAVING, then the takeCensus action will keep taking a census until
+    // the inverted property matches the inverted state. If the snapshot is
+    // still in the process of being saved or read, the takeSnapshotAndCensus
+    // task action will follow through and ensure that a census is taken.
+    if ((snapshot.census && snapshot.census.state === censusState.SAVED) ||
+        !snapshot.census) {
+      yield dispatch(takeCensus(heapWorker, snapshot.id));
+    }
+  };
+};
+
+/**
+ * Refresh the selected snapshot's tree map data, if need be (for example,
+ * display configuration changed).
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const refreshSelectedTreeMap = exports.refreshSelectedTreeMap = function (heapWorker) {
+  return function* (dispatch, getState) {
+    let snapshot = getState().snapshots.find(s => s.selected);
+    if (!snapshot || snapshot.state !== states.READ) {
+      return;
+    }
+
+    // Intermediate snapshot states will get handled by the task action that is
+    // orchestrating them. For example, if the snapshot census's state is
+    // SAVING, then the takeCensus action will keep taking a census until
+    // the inverted property matches the inverted state. If the snapshot is
+    // still in the process of being saved or read, the takeSnapshotAndCensus
+    // task action will follow through and ensure that a census is taken.
+    if ((snapshot.treeMap && snapshot.treeMap.state === treeMapState.SAVED) ||
+        !snapshot.treeMap) {
+      yield dispatch(takeTreeMap(heapWorker, snapshot.id));
+    }
+  };
+};
+
+/**
+ * Request that the `HeapAnalysesWorker` compute the dominator tree for the
+ * snapshot with the given `id`.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {SnapshotId} id
+ *
+ * @returns {Promise<DominatorTreeId>}
+ */
+const computeDominatorTree = exports.computeDominatorTree =
+TaskCache.declareCacheableTask({
+  getCacheKey(_, id) {
+    return id;
+  },
+
+  task: function* (heapWorker, id, removeFromCache, dispatch, getState) {
+    const snapshot = getSnapshot(getState(), id);
+    assert(!(snapshot.dominatorTree && snapshot.dominatorTree.dominatorTreeId),
+           "Should not re-compute dominator trees");
+
+    dispatch({ type: actions.COMPUTE_DOMINATOR_TREE_START, id });
+
+    let dominatorTreeId;
+    try {
+      dominatorTreeId = yield heapWorker.computeDominatorTree(snapshot.path);
+    } catch (error) {
+      removeFromCache();
+      reportException("actions/snapshot/computeDominatorTree", error);
+      dispatch({ type: actions.DOMINATOR_TREE_ERROR, id, error });
+      return null;
+    }
+
+    removeFromCache();
+    dispatch({ type: actions.COMPUTE_DOMINATOR_TREE_END, id, dominatorTreeId });
+    return dominatorTreeId;
+  }
+});
+
+/**
+ * Get the partial subtree, starting from the root, of the
+ * snapshot-with-the-given-id's dominator tree.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {SnapshotId} id
+ *
+ * @returns {Promise<DominatorTreeNode>}
+ */
+const fetchDominatorTree = exports.fetchDominatorTree =
+TaskCache.declareCacheableTask({
+  getCacheKey(_, id) {
+    return id;
+  },
+
+  task: function* (heapWorker, id, removeFromCache, dispatch, getState) {
+    const snapshot = getSnapshot(getState(), id);
+    assert(dominatorTreeIsComputed(snapshot),
+           "Should have dominator tree model and it should be computed");
+
+    let display;
+    let root;
+    do {
+      display = getState().labelDisplay;
+      assert(display && display.breakdown,
+             `Should have a breakdown to describe nodes with, got: ${uneval(display)}`);
+
+      dispatch({ type: actions.FETCH_DOMINATOR_TREE_START, id, display });
+
+      try {
+        root = yield heapWorker.getDominatorTree({
+          dominatorTreeId: snapshot.dominatorTree.dominatorTreeId,
+          breakdown: display.breakdown,
+          maxRetainingPaths: Preferences.get("devtools.memory.max-retaining-paths"),
+        });
+      } catch (error) {
+        removeFromCache();
+        reportException("actions/snapshot/fetchDominatorTree", error);
+        dispatch({ type: actions.DOMINATOR_TREE_ERROR, id, error });
+        return null;
+      }
+    }
+    while (display !== getState().labelDisplay);
+
+    removeFromCache();
+    dispatch({ type: actions.FETCH_DOMINATOR_TREE_END, id, root });
+    telemetry.countDominatorTree({ display });
+    return root;
+  }
+});
+
+/**
+ * Fetch the immediately dominated children represented by the placeholder
+ * `lazyChildren` from snapshot-with-the-given-id's dominator tree.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {SnapshotId} id
+ * @param {DominatorTreeLazyChildren} lazyChildren
+ */
+const fetchImmediatelyDominated = exports.fetchImmediatelyDominated =
+TaskCache.declareCacheableTask({
+  getCacheKey(_, id, lazyChildren) {
+    return `${id}-${lazyChildren.key()}`;
+  },
+
+  task: function* (heapWorker, id, lazyChildren, removeFromCache, dispatch, getState) {
+    const snapshot = getSnapshot(getState(), id);
+    assert(snapshot.dominatorTree, "Should have dominator tree model");
+    assert(snapshot.dominatorTree.state === dominatorTreeState.LOADED ||
+           snapshot.dominatorTree.state === dominatorTreeState.INCREMENTAL_FETCHING,
+           "Cannot fetch immediately dominated nodes in a dominator tree unless " +
+           " the dominator tree has already been computed");
+
+    let display;
+    let response;
+    do {
+      display = getState().labelDisplay;
+      assert(display, "Should have a display to describe nodes with.");
+
+      dispatch({ type: actions.FETCH_IMMEDIATELY_DOMINATED_START, id });
+
+      try {
+        response = yield heapWorker.getImmediatelyDominated({
+          dominatorTreeId: snapshot.dominatorTree.dominatorTreeId,
+          breakdown: display.breakdown,
+          nodeId: lazyChildren.parentNodeId(),
+          startIndex: lazyChildren.siblingIndex(),
+          maxRetainingPaths: Preferences.get("devtools.memory.max-retaining-paths"),
+        });
+      } catch (error) {
+        removeFromCache();
+        reportException("actions/snapshot/fetchImmediatelyDominated", error);
+        dispatch({ type: actions.DOMINATOR_TREE_ERROR, id, error });
+        return null;
+      }
+    }
+    while (display !== getState().labelDisplay);
+
+    removeFromCache();
+    dispatch({
+      type: actions.FETCH_IMMEDIATELY_DOMINATED_END,
+      id,
+      path: response.path,
+      nodes: response.nodes,
+      moreChildrenAvailable: response.moreChildrenAvailable,
+    });
+  }
+});
+
+/**
+ * Compute and then fetch the dominator tree of the snapshot with the given
+ * `id`.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {SnapshotId} id
+ *
+ * @returns {Promise<DominatorTreeNode>}
+ */
+const computeAndFetchDominatorTree = exports.computeAndFetchDominatorTree =
+TaskCache.declareCacheableTask({
+  getCacheKey(_, id) {
+    return id;
+  },
+
+  task: function* (heapWorker, id, removeFromCache, dispatch, getState) {
+    const dominatorTreeId = yield dispatch(computeDominatorTree(heapWorker, id));
+    if (dominatorTreeId === null) {
+      removeFromCache();
+      return null;
+    }
+
+    const root = yield dispatch(fetchDominatorTree(heapWorker, id));
+    removeFromCache();
+
+    if (!root) {
+      return null;
+    }
+
+    return root;
+  }
+});
+
+/**
+ * Update the currently selected snapshot's dominator tree.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const refreshSelectedDominatorTree = exports.refreshSelectedDominatorTree = function (heapWorker) {
+  return function* (dispatch, getState) {
+    let snapshot = getState().snapshots.find(s => s.selected);
+    if (!snapshot) {
+      return;
+    }
+
+    if (snapshot.dominatorTree &&
+        !(snapshot.dominatorTree.state === dominatorTreeState.COMPUTED ||
+          snapshot.dominatorTree.state === dominatorTreeState.LOADED ||
+          snapshot.dominatorTree.state === dominatorTreeState.INCREMENTAL_FETCHING)) {
+      return;
+    }
+
+    if (snapshot.state === states.READ) {
+      if (snapshot.dominatorTree) {
+        yield dispatch(fetchDominatorTree(heapWorker, snapshot.id));
+      } else {
+        yield dispatch(computeAndFetchDominatorTree(heapWorker, snapshot.id));
+      }
+    } else {
+        // If there was an error, we can't continue. If we are still saving or
+        // reading the snapshot, then takeSnapshotAndCensus will finish the job
+        // for us.
+      return;
+    }
+  };
+};
+
+/**
+ * Select the snapshot with the given id.
+ *
+ * @param {snapshotId} id
+ * @see {Snapshot} model defined in devtools/client/memory/models.js
+ */
+const selectSnapshot = exports.selectSnapshot = function (id) {
+  return {
+    type: actions.SELECT_SNAPSHOT,
+    id
+  };
+};
+
+/**
+ * Delete all snapshots that are in the READ or ERROR state
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+const clearSnapshots = exports.clearSnapshots = function (heapWorker) {
+  return function* (dispatch, getState) {
+    let snapshots = getState().snapshots.filter(s => {
+      let snapshotReady = s.state === states.READ || s.state === states.ERROR;
+      let censusReady = (s.treeMap && s.treeMap.state === treeMapState.SAVED) ||
+                        (s.census && s.census.state === censusState.SAVED);
+
+      return snapshotReady && censusReady;
+    });
+
+    let ids = snapshots.map(s => s.id);
+
+    dispatch({ type: actions.DELETE_SNAPSHOTS_START, ids });
+
+    if (getState().diffing) {
+      dispatch(diffing.toggleDiffing());
+    }
+    if (getState().individuals) {
+      dispatch(view.popView());
+    }
+
+    yield Promise.all(snapshots.map(snapshot => {
+      return heapWorker.deleteHeapSnapshot(snapshot.path).catch(error => {
+        reportException("clearSnapshots", error);
+        dispatch({ type: actions.SNAPSHOT_ERROR, id: snapshot.id, error });
+      });
+    }));
+
+    dispatch({ type: actions.DELETE_SNAPSHOTS_END, ids });
+  };
+};
+
+/**
+ * Delete a snapshot
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ * @param {snapshotModel} snapshot
+ */
+const deleteSnapshot = exports.deleteSnapshot = function (heapWorker, snapshot) {
+  return function* (dispatch, getState) {
+    dispatch({ type: actions.DELETE_SNAPSHOTS_START, ids: [snapshot.id] });
+
+    try {
+      yield heapWorker.deleteHeapSnapshot(snapshot.path);
+    } catch (error) {
+      reportException("deleteSnapshot", error);
+      dispatch({ type: actions.SNAPSHOT_ERROR, id: snapshot.id, error });
+    }
+
+    dispatch({ type: actions.DELETE_SNAPSHOTS_END, ids: [snapshot.id] });
+  };
+};
+
+/**
+ * Expand the given node in the snapshot's census report.
+ *
+ * @param {CensusTreeNode} node
+ */
+const expandCensusNode = exports.expandCensusNode = function (id, node) {
+  return {
+    type: actions.EXPAND_CENSUS_NODE,
+    id,
+    node,
+  };
+};
+
+/**
+ * Collapse the given node in the snapshot's census report.
+ *
+ * @param {CensusTreeNode} node
+ */
+const collapseCensusNode = exports.collapseCensusNode = function (id, node) {
+  return {
+    type: actions.COLLAPSE_CENSUS_NODE,
+    id,
+    node,
+  };
+};
+
+/**
+ * Focus the given node in the snapshot's census's report.
+ *
+ * @param {SnapshotId} id
+ * @param {DominatorTreeNode} node
+ */
+const focusCensusNode = exports.focusCensusNode = function (id, node) {
+  return {
+    type: actions.FOCUS_CENSUS_NODE,
+    id,
+    node,
+  };
+};
+
+/**
+ * Expand the given node in the snapshot's dominator tree.
+ *
+ * @param {DominatorTreeTreeNode} node
+ */
+const expandDominatorTreeNode = exports.expandDominatorTreeNode = function (id, node) {
+  return {
+    type: actions.EXPAND_DOMINATOR_TREE_NODE,
+    id,
+    node,
+  };
+};
+
+/**
+ * Collapse the given node in the snapshot's dominator tree.
+ *
+ * @param {DominatorTreeTreeNode} node
+ */
+const collapseDominatorTreeNode = exports.collapseDominatorTreeNode = function (id, node) {
+  return {
+    type: actions.COLLAPSE_DOMINATOR_TREE_NODE,
+    id,
+    node,
+  };
+};
+
+/**
+ * Focus the given node in the snapshot's dominator tree.
+ *
+ * @param {SnapshotId} id
+ * @param {DominatorTreeNode} node
+ */
+const focusDominatorTreeNode = exports.focusDominatorTreeNode = function (id, node) {
+  return {
+    type: actions.FOCUS_DOMINATOR_TREE_NODE,
+    id,
+    node,
+  };
+};
diff --git a/devtools/client/memory/actions/task-cache.js b/devtools/client/memory/actions/task-cache.js
new file mode 100644
index 000000000..14e44d0c3
--- /dev/null
+++ b/devtools/client/memory/actions/task-cache.js
@@ -0,0 +1,99 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+
+/**
+ * The `TaskCache` allows for re-using active tasks when spawning a second task
+ * would simply duplicate work and is unnecessary. It maps from a task's unique
+ * key to the promise of its result.
+ */
+const TaskCache = module.exports = class TaskCache {
+  constructor() {
+    this._cache = new Map();
+  }
+
+  /**
+   * Get the promise keyed by the given unique `key`, if one exists.
+   *
+   * @param {Any} key
+   * @returns {Promise<Any> | undefined}
+   */
+  get(key) {
+    return this._cache.get(key);
+  }
+
+  /**
+   * Put the task result promise in the cache and associate it with the given
+   * `key` which must not already have an entry in the cache.
+   *
+   * @param {Any} key
+   * @param {Promise<Any>} promise
+   */
+  put(key, promise) {
+    assert(!this._cache.has(key),
+           "We should not override extant entries");
+
+    this._cache.set(key, promise);
+  }
+
+  /**
+   * Remove the cache entry with the given key.
+   *
+   * @param {Any} key
+   */
+  remove(key) {
+    assert(this._cache.has(key),
+           `Should have an extant entry for key = ${key}`);
+
+    this._cache.delete(key);
+  }
+};
+
+/**
+ * Create a new action-orchestrating task that is automatically cached. The
+ * tasks themselves are responsible from removing themselves from the cache.
+ *
+ * @param {Function(...args) -> Any} getCacheKey
+ * @param {Generator(...args) -> Any} task
+ *
+ * @returns Cacheable, Action-Creating Task
+ */
+TaskCache.declareCacheableTask = function ({ getCacheKey, task }) {
+  const cache = new TaskCache();
+
+  return function (...args) {
+    return function* (dispatch, getState) {
+      const key = getCacheKey(...args);
+
+      const extantResult = cache.get(key);
+      if (extantResult) {
+        return extantResult;
+      }
+
+      // Ensure that we have our new entry in the cache *before* dispatching the
+      // task!
+      let resolve;
+      cache.put(key, new Promise(r => {
+        resolve = r;
+      }));
+
+      resolve(dispatch(function* () {
+        try {
+          args.push(() => cache.remove(key), dispatch, getState);
+          return yield* task(...args);
+        } catch (error) {
+          // Don't perma-cache errors.
+          if (cache.get(key)) {
+            cache.remove(key);
+          }
+          throw error;
+        }
+      }));
+
+      return yield cache.get(key);
+    };
+  };
+};
diff --git a/devtools/client/memory/actions/tree-map-display.js b/devtools/client/memory/actions/tree-map-display.js
new file mode 100644
index 000000000..e4ab9988c
--- /dev/null
+++ b/devtools/client/memory/actions/tree-map-display.js
@@ -0,0 +1,37 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+const { actions } = require("../constants");
+const { refresh } = require("./refresh");
+/**
+ * Sets the tree map display as the current display and refreshes the tree map
+ * census.
+ */
+exports.setTreeMapAndRefresh = function (heapWorker, display) {
+  return function* (dispatch, getState) {
+    dispatch(setTreeMap(display));
+    yield dispatch(refresh(heapWorker));
+  };
+};
+
+/**
+ * Clears out all cached census data in the snapshots and sets new display data
+ * for tree maps.
+ *
+ * @param {treeMapModel} display
+ */
+const setTreeMap = exports.setTreeMap = function (display) {
+  assert(typeof display === "object"
+         && display
+         && display.breakdown
+         && display.breakdown.by,
+    `Breakdowns must be an object with a \`by\` property, attempted to set: ${uneval(display)}`);
+
+  return {
+    type: actions.SET_TREE_MAP_DISPLAY,
+    display,
+  };
+};
diff --git a/devtools/client/memory/actions/view.js b/devtools/client/memory/actions/view.js
new file mode 100644
index 000000000..5ff508840
--- /dev/null
+++ b/devtools/client/memory/actions/view.js
@@ -0,0 +1,67 @@
+/* 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 { assert } = require("devtools/shared/DevToolsUtils");
+const { actions } = require("../constants");
+const { findSelectedSnapshot } = require("../utils");
+const refresh = require("./refresh");
+
+/**
+ * Change the currently selected view.
+ *
+ * @param {viewState} view
+ */
+const changeView = exports.changeView = function (view) {
+  return function (dispatch, getState) {
+    dispatch({
+      type: actions.CHANGE_VIEW,
+      newViewState: view,
+      oldDiffing: getState().diffing,
+      oldSelected: findSelectedSnapshot(getState()),
+    });
+  };
+};
+
+/**
+ * Given that we are in the INDIVIDUALS view state, go back to the state we were
+ * in before.
+ */
+const popView = exports.popView = function () {
+  return function (dispatch, getState) {
+    const { previous } = getState().view;
+    assert(previous);
+    dispatch({
+      type: actions.POP_VIEW,
+      previousView: previous,
+    });
+  };
+};
+
+/**
+ * Change the currently selected view and ensure all our data is up to date from
+ * the heap worker.
+ *
+ * @param {viewState} view
+ * @param {HeapAnalysesClient} heapWorker
+ */
+exports.changeViewAndRefresh = function (view, heapWorker) {
+  return function* (dispatch, getState) {
+    dispatch(changeView(view));
+    yield dispatch(refresh.refresh(heapWorker));
+  };
+};
+
+/**
+ * Given that we are in the INDIVIDUALS view state, go back to the state we were
+ * previously in and refresh our data.
+ *
+ * @param {HeapAnalysesClient} heapWorker
+ */
+exports.popViewAndRefresh = function (heapWorker) {
+  return function* (dispatch, getState) {
+    dispatch(popView());
+    yield dispatch(refresh.refresh(heapWorker));
+  };
+};