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diff --git a/dom/media/doctor/DDMediaLogs.h b/dom/media/doctor/DDMediaLogs.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 DDMediaLogs_h_
+#define DDMediaLogs_h_
+
+#include "DDLifetimes.h"
+#include "DDMediaLog.h"
+#include "mozilla/MozPromise.h"
+#include "MultiWriterQueue.h"
+
+namespace mozilla {
+
+// Main object managing all processed logs, and yet-unprocessed messages.
+struct DDMediaLogs {
+ public:
+  // Construct a DDMediaLogs object if possible.
+  struct ConstructionResult {
+    nsresult mRv;
+    DDMediaLogs* mMediaLogs;
+  };
+  static ConstructionResult New();
+
+  // If not already shutdown, performs normal end-of-life processing, and shuts
+  // down the processing thread (blocking).
+  ~DDMediaLogs();
+
+  // Shutdown the processing thread (blocking), and free as much memory as
+  // possible.
+  void Panic();
+
+  inline void Log(const char* aSubjectTypeName, const void* aSubjectPointer,
+                  DDLogCategory aCategory, const char* aLabel,
+                  DDLogValue&& aValue) {
+    if (mMessagesQueue.PushF(
+            [&](DDLogMessage& aMessage, MessagesQueue::Index i) {
+              aMessage.mIndex = i;
+              aMessage.mTimeStamp = DDNow();
+              aMessage.mObject.Set(aSubjectTypeName, aSubjectPointer);
+              aMessage.mCategory = aCategory;
+              aMessage.mLabel = aLabel;
+              aMessage.mValue = std::move(aValue);
+            })) {
+      // Filled a buffer-full of messages, process it in another thread.
+      DispatchProcessLog();
+    }
+  }
+
+  // Process the log right now; should only be used on the processing thread,
+  // or after shutdown for end-of-life log retrieval. Work includes:
+  // - Processing incoming buffers, to update object lifetimes and links;
+  // - Resolve pending promises that requested logs;
+  // - Clean-up old logs from memory.
+  void ProcessLog();
+
+  using LogMessagesPromise =
+      MozPromise<nsCString, nsresult, /* IsExclusive = */ true>;
+
+  // Retrieve all messages associated with an HTMLMediaElement.
+  // This will trigger an async processing run (to ensure most recent messages
+  // get retrieved too), and the returned promise will be resolved with all
+  // found log messages.
+  RefPtr<LogMessagesPromise> RetrieveMessages(
+      const dom::HTMLMediaElement* aMediaElement);
+
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
+
+ private:
+  // Constructor, takes the given thread to use for log processing.
+  explicit DDMediaLogs(nsCOMPtr<nsIThread>&& aThread);
+
+  // Shutdown the processing thread, blocks until that thread exits.
+  // If aPanic is true, just free as much memory as possible.
+  // Otherwise, perform a final processing run, output end-logs (if enabled).
+  void Shutdown(bool aPanic);
+
+  // Get the log of yet-unassociated messages.
+  DDMediaLog& LogForUnassociatedMessages();
+  const DDMediaLog& LogForUnassociatedMessages() const;
+
+  // Get the log for the given HTMLMediaElement. Returns nullptr if there is no
+  // such log yet.
+  DDMediaLog* GetLogFor(const dom::HTMLMediaElement* aMediaElement);
+
+  // Get the log for the given HTMLMediaElement.
+  // A new log is created if that element didn't already have one.
+  DDMediaLog& LogFor(const dom::HTMLMediaElement* aMediaElement);
+
+  // Associate a lifetime, and all its already-linked lifetimes, with an
+  // HTMLMediaElement.
+  // All messages involving the modified lifetime(s) are moved to the
+  // corresponding log.
+  void SetMediaElement(DDLifetime& aLifetime,
+                       const dom::HTMLMediaElement* aMediaElement);
+
+  // Find the lifetime corresponding to an object (known type and pointer) that
+  // was known to be alive at aIndex.
+  // If there is no such lifetime yet, create it with aTimeStamp as implicit
+  // construction timestamp.
+  // If the object is of type HTMLMediaElement, run SetMediaElement() on it.
+  DDLifetime& FindOrCreateLifetime(const DDLogObject& aObject,
+                                   DDMessageIndex aIndex,
+                                   const DDTimeStamp& aTimeStamp);
+
+  // Link two lifetimes together (at a given time corresponding to aIndex).
+  // If only one is associated with an HTMLMediaElement, run SetMediaElement on
+  // the other one.
+  void LinkLifetimes(DDLifetime& aParentLifetime, const char* aLinkName,
+                     DDLifetime& aChildLifetime, DDMessageIndex aIndex);
+
+  // Unlink all lifetimes linked to aLifetime; only used to know when links
+  // expire, so that they won't be used after this time.
+  void UnlinkLifetime(DDLifetime& aLifetime, DDMessageIndex aIndex);
+
+  // Unlink two lifetimes; only used to know when a link expires, so that it
+  // won't be used after this time.
+  void UnlinkLifetimes(DDLifetime& aParentLifetime, DDLifetime& aChildLifetime,
+                       DDMessageIndex aIndex);
+
+  // Remove all links involving aLifetime from the database.
+  void DestroyLifetimeLinks(const DDLifetime& aLifetime);
+
+  // Process all incoming log messages.
+  // This will create the appropriate DDLifetime and links objects, and then
+  // move processed messages to logs associated with different
+  // HTMLMediaElements.
+  void ProcessBuffer();
+
+  // Pending promises (added by RetrieveMessages) are resolved with all new
+  // log messages corresponding to requested HTMLMediaElements -- These
+  // messages are removed from our logs.
+  void FulfillPromises();
+
+  // Remove processed messages that have a low chance of being requested,
+  // based on the assumption that users/scripts will regularly call
+  // RetrieveMessages for HTMLMediaElements they are interested in.
+  void CleanUpLogs();
+
+  // Request log-processing on the processing thread. Thread-safe.
+  nsresult DispatchProcessLog();
+
+  // Request log-processing on the processing thread.
+  nsresult DispatchProcessLog(const MutexAutoLock& aProofOfLock);
+
+  using MessagesQueue =
+      MultiWriterQueue<DDLogMessage, MultiWriterQueueDefaultBufferSize,
+                       MultiWriterQueueReaderLocking_None>;
+  MessagesQueue mMessagesQueue;
+
+  DDLifetimes mLifetimes;
+
+  // mMediaLogs[0] contains unsorted message (with mMediaElement=nullptr).
+  // mMediaLogs[1+] contains sorted messages for each media element.
+  nsTArray<DDMediaLog> mMediaLogs;
+
+  struct DDObjectLink {
+    const DDLogObject mParent;
+    const DDLogObject mChild;
+    const char* const mLinkName;
+    const DDMessageIndex mLinkingIndex;
+    Maybe<DDMessageIndex> mUnlinkingIndex;
+
+    DDObjectLink(DDLogObject aParent, DDLogObject aChild, const char* aLinkName,
+                 DDMessageIndex aLinkingIndex)
+        : mParent(aParent),
+          mChild(aChild),
+          mLinkName(aLinkName),
+          mLinkingIndex(aLinkingIndex),
+          mUnlinkingIndex(Nothing{}) {}
+  };
+  // Links between live objects, updated while messages are processed.
+  nsTArray<DDObjectLink> mObjectLinks;
+
+  // Protects members below.
+  Mutex mMutex MOZ_UNANNOTATED;
+
+  // Processing thread.
+  nsCOMPtr<nsIThread> mThread;
+
+  struct PendingPromise {
+    MozPromiseHolder<LogMessagesPromise> mPromiseHolder;
+    const dom::HTMLMediaElement* mMediaElement;
+  };
+  // Most cases should have 1 media panel requesting 1 promise at a time.
+  AutoTArray<PendingPromise, 2> mPendingPromises;
+};
+
+}  // namespace mozilla
+
+#endif  // DDMediaLogs_h_