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diff --git a/js/src/vm/TraceLoggingGraph.h b/js/src/vm/TraceLoggingGraph.h
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+++ b/js/src/vm/TraceLoggingGraph.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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/. */
+
+#ifndef TraceLoggingGraph_h
+#define TraceLoggingGraph_h
+
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/TimeStamp.h"
+
+#include "js/TypeDecls.h"
+#include "vm/MutexIDs.h"
+#include "vm/TraceLoggingTypes.h"
+
+// clang-format off
+/*
+ * The output of a tracelogging session is saved in /tmp/tl-data.json.
+ * The format of that file is a JS array per tracelogger (=thread), with a map
+ * containing:
+ *  - dict:   Name of the file containing a json table with the log text.
+ *            All other files only contain a index to this table when logging.
+ *  - events: Name of the file containing a flat list of log events saved
+ *            in binary format.
+ *            (64bit: Time Stamp Counter, 32bit index to dict)
+ *  - tree:   Name of the file containing the events with duration. The content
+ *            is already in a tree data structure. This is also saved in a
+ *            binary file.
+ *  - treeFormat: The format used to encode the tree. By default "64,64,31,1,32".
+ *                There are currently no other formats to save the tree.
+ *     - 64,64,31,1,32 signifies how many bytes are used for the different
+ *       parts of the tree.
+ *       => 64 bits: Time Stamp Counter of start of event.
+ *       => 64 bits: Time Stamp Counter of end of event.
+ *       => 31 bits: Index to dict file containing the log text.
+ *       =>  1 bit:  Boolean signifying if this entry has children.
+ *                   When true, the child can be found just right after this
+ *                   entry.
+ *       => 32 bits: Containing the ID of the next event on the same depth
+ *                   or 0 if there isn't an event on the same depth anymore.
+ *
+ *        /-> The position in the file. Id is this divided by size of entry.
+ *        |   So in this case this would be 1 (192bits per entry).
+ *        |                              /-> Indicates there are children. The
+ *        |                              |   first child is located at current
+ *        |                              |   ID + 1. So 1 + 1 in this case: 2.
+ *        |                              |   Or 0x00180 in the tree file.
+ *        |                              | /-> Next event on the same depth is
+ *        |                              | |    located at 4. So 0x00300 in the
+ *        |                              | |    tree file.
+ *       0x0000C0: [start, end, dictId, 1, 4]
+ *
+ *
+ *       Example:
+ *                          0x0: [start, end, dictId, 1, 0]
+ *                                        |
+ *                      /----------------------------------\
+ *                      |                                  |
+ *       0xC0: [start, end, dictId, 0, 2]      0x180 [start, end, dictId, 1, 0]
+ *                                                      |
+ *                                  /----------------------------------\
+ *                                  |                                  |
+ *         0x240: [start, end, dictId, 0, 4]    0x300 [start, end, dictId, 0, 0]
+ */
+// clang-format on
+
+namespace js {
+void DestroyTraceLoggerGraphState();
+size_t SizeOfTraceLogGraphState(mozilla::MallocSizeOf mallocSizeOf);
+}  // namespace js
+
+class TraceLoggerGraphState {
+  uint32_t numLoggers;
+  uint32_t pid_;
+
+  // File pointer to the "tl-data.json" file. (Explained above).
+  FILE* out;
+
+#ifdef DEBUG
+  bool initialized;
+#endif
+
+ public:
+  js::Mutex lock;
+
+ public:
+  TraceLoggerGraphState()
+      : numLoggers(0),
+        pid_(0),
+        out(nullptr)
+#ifdef DEBUG
+        ,
+        initialized(false)
+#endif
+        ,
+        lock(js::mutexid::TraceLoggerGraphState) {
+  }
+
+  bool init();
+  ~TraceLoggerGraphState();
+
+  uint32_t nextLoggerId();
+  uint32_t pid() { return pid_; }
+
+  size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
+  size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
+    return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
+  }
+};
+
+namespace js {
+class TraceLoggerThread;
+}  // namespace js
+
+class TraceLoggerGraph {
+  // This is needed so that we can write the data to the JSON writer from the TL
+  // thread class.
+  friend class js::TraceLoggerThread;
+
+ private:
+  // The layout of the tree in memory and in the log file. Readable by JS
+  // using TypedArrays.
+  struct TreeEntry {
+    uint64_t start_;
+    uint64_t stop_;
+    union {
+      struct {
+        uint32_t textId_ : 31;
+        uint32_t hasChildren_ : 1;
+      } s;
+      uint32_t value_;
+    } u;
+    uint32_t nextId_;
+
+    TreeEntry(uint64_t start, uint64_t stop, uint32_t textId, bool hasChildren,
+              uint32_t nextId) {
+      start_ = start;
+      stop_ = stop;
+      u.s.textId_ = textId;
+      u.s.hasChildren_ = hasChildren;
+      nextId_ = nextId;
+    }
+    TreeEntry() : start_(0), stop_(0), u{}, nextId_(0) {}
+    uint64_t start() { return start_; }
+    uint64_t stop() { return stop_; }
+    uint32_t textId() { return u.s.textId_; }
+    bool hasChildren() { return u.s.hasChildren_; }
+    uint32_t nextId() { return nextId_; }
+    void setStart(uint64_t start) { start_ = start; }
+    void setStop(uint64_t stop) { stop_ = stop; }
+    void setTextId(uint32_t textId) {
+      MOZ_ASSERT(textId < uint32_t(1 << 31));
+      u.s.textId_ = textId;
+    }
+    void setHasChildren(bool hasChildren) { u.s.hasChildren_ = hasChildren; }
+    void setNextId(uint32_t nextId) { nextId_ = nextId; }
+  };
+
+  // Helper structure for keeping track of the current entries in
+  // the tree. Pushed by `start(id)`, popped by `stop(id)`. The active flag
+  // is used to know if a subtree doesn't need to get logged.
+  struct StackEntry {
+    uint32_t treeId_;
+    uint32_t lastChildId_;
+    struct {
+      uint32_t textId_ : 31;
+      uint32_t active_ : 1;
+    } s;
+    StackEntry(uint32_t treeId, uint32_t lastChildId, bool active = true)
+        : treeId_(treeId), lastChildId_(lastChildId) {
+      s.textId_ = 0;
+      s.active_ = active;
+    }
+    uint32_t treeId() { return treeId_; }
+    uint32_t lastChildId() { return lastChildId_; }
+    uint32_t textId() { return s.textId_; }
+    bool active() { return s.active_; }
+    void setTreeId(uint32_t treeId) { treeId_ = treeId; }
+    void setLastChildId(uint32_t lastChildId) { lastChildId_ = lastChildId; }
+    void setTextId(uint32_t textId) {
+      MOZ_ASSERT(textId < uint32_t(1 << 31));
+      s.textId_ = textId;
+    }
+    void setActive(bool active) { s.active_ = active; }
+  };
+
+ public:
+  TraceLoggerGraph() = default;
+  ~TraceLoggerGraph();
+
+  bool init(uint64_t timestamp, bool graphFileEnabled);
+
+  // Link a textId with a particular text.
+  void addTextId(uint32_t id, const char* text);
+  void addTextId(uint32_t id, const char* text, mozilla::Maybe<uint32_t>& line,
+                 mozilla::Maybe<uint32_t>& column);
+
+  // Create a tree out of all the given events.
+  void log(ContinuousSpace<EventEntry>& events, mozilla::TimeStamp startTime);
+
+  static size_t treeSizeFlushLimit() {
+    // Allow tree size to grow to 100MB.
+    return 100 * 1024 * 1024 / sizeof(TreeEntry);
+  }
+
+  uint32_t nextTextId() { return nextTextId_; }
+
+  size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
+  size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
+
+ private:
+  bool failed = false;
+  bool enabled = false;
+  uint32_t nextTextId_ = 0;
+
+  FILE* dictFile = nullptr;
+  FILE* treeFile = nullptr;
+  FILE* eventFile = nullptr;
+
+  ContinuousSpace<TreeEntry> tree;
+  ContinuousSpace<StackEntry> stack;
+  uint32_t treeOffset = 0;
+
+  // Helper functions that convert a TreeEntry in different endianness
+  // in place.
+  void entryToBigEndian(TreeEntry* entry);
+  void entryToSystemEndian(TreeEntry* entry);
+
+  // Helper functions to get/save a tree from file.
+  bool getTreeEntry(uint32_t treeId, TreeEntry* entry);
+  bool saveTreeEntry(uint32_t treeId, TreeEntry* entry);
+
+  // Return the first StackEntry that is active.
+  StackEntry& getActiveAncestor();
+
+  // This contains the meat of startEvent, except the test for enough space,
+  // the test if tracelogger is enabled and the timestamp computation.
+  void startEvent(uint32_t id, uint64_t timestamp);
+  bool startEventInternal(uint32_t id, uint64_t timestamp);
+
+  // Update functions that can adjust the items in the tree,
+  // both in memory or already written to disk.
+  bool updateHasChildren(uint32_t treeId, bool hasChildren = true);
+  bool updateNextId(uint32_t treeId, uint32_t nextId);
+  bool updateStop(uint32_t treeId, uint64_t timestamp);
+
+  // Flush the tree.
+  bool flush();
+
+  // Stop a tree event.
+  void stopEvent(uint32_t id, uint64_t timestamp);
+  void stopEvent(uint64_t timestamp);
+
+  // Log an (non-tree) event.
+  void logTimestamp(uint32_t id, uint64_t timestamp);
+
+  // Disable logging and forcefully report all not yet stopped tree events
+  // as stopped.
+  void disable(uint64_t timestamp);
+};
+
+#endif /* TraceLoggingGraph_h */