Bug 932865 - Add way for telemetry to iterate over active threads; r=froydnj

xpcom/threads/BackgroundHangMonitor.cpp

@@ -7,6 +7,7 @@
 #include "mozilla/LinkedList.h"
 #include "mozilla/Monitor.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/ThreadHangStats.h"
 #include "mozilla/ThreadLocal.h"
 
 #include "prinrval.h"
@@ -103,8 +104,6 @@ public:
     if (!sTlsKey.init()) {}
   }
 
-  // Name of the thread
-  const nsAutoCString mThreadName;
   // Hang timeout in ticks
   const PRIntervalTime mTimeout;
   // PermaHang timeout in ticks
@@ -117,6 +116,8 @@ public:
   bool mHanging;
   // Is the thread in a waiting state
   bool mWaiting;
+  // Statistics for telemetry
+  Telemetry::ThreadHangStats mStats;
 
   BackgroundHangThread(const char* aName,
                        uint32_t aTimeoutMs,
@@ -292,13 +293,13 @@ BackgroundHangThread::BackgroundHangThread(const char* aName,
                                            uint32_t aMaxTimeoutMs)
   : mManager(BackgroundHangManager::sInstance)
   , mThreadID(PR_GetCurrentThread())
-  , mThreadName(aName)
   , mTimeout(PR_MillisecondsToInterval(aTimeoutMs))
   , mMaxTimeout(PR_MillisecondsToInterval(aMaxTimeoutMs))
   , mInterval(mManager->mIntervalNow)
   , mHangStart(mInterval)
   , mHanging(false)
   , mWaiting(true)
+  , mStats(aName)
 {
   if (sTlsKey.initialized()) {
     sTlsKey.set(this);
@@ -440,4 +441,25 @@ BackgroundHangMonitor::NotifyWait()
   mThread->NotifyWait();
 }
 
+
+/* Because we are iterating through the BackgroundHangThread linked list,
+   we need to take a lock. Using MonitorAutoLock as a base class makes
+   sure all of that is taken care of for us. */
+BackgroundHangMonitor::ThreadHangStatsIterator::ThreadHangStatsIterator()
+  : MonitorAutoLock(BackgroundHangManager::sInstance->mLock)
+  , mThread(BackgroundHangManager::sInstance->mHangThreads.getFirst())
+{
+}
+
+Telemetry::ThreadHangStats*
+BackgroundHangMonitor::ThreadHangStatsIterator::GetNext()
+{
+  if (!mThread) {
+    return nullptr;
+  }
+  Telemetry::ThreadHangStats* stats = &mThread->mStats;
+  mThread = mThread->getNext();
+  return stats;
+}
+
 } // namespace mozilla

xpcom/threads/BackgroundHangMonitor.h

@@ -7,11 +7,16 @@
 #define mozilla_BackgroundHangMonitor_h
 
 #include "mozilla/RefPtr.h"
+#include "mozilla/Monitor.h"
 
 #include <stdint.h>
 
 namespace mozilla {
 
+namespace Telemetry {
+class ThreadHangStats;
+};
+
 class BackgroundHangThread;
 
 /**
@@ -101,6 +106,44 @@ private:
   RefPtr<BackgroundHangThread> mThread;
 
 public:
+  /**
+   * ThreadHangStatsIterator is used to iterate through the ThreadHangStats
+   * associated with each active monitored thread. Because of an internal
+   * lock while this object is alive, a thread must use only one instance
+   * of this class at a time and must iterate through the list as fast as
+   * possible. The following example shows using the iterator:
+   *
+   * {
+   *   // Scope the iter variable so it's destroyed as soon as we're done
+   *   BackgroundHangMonitor::ThreadHangStatsIterator iter;
+   *   for (ThreadHangStats* histogram = iter.GetNext();
+   *        histogram; histogram = iter.GetNext()) {
+   *     // Process histogram
+   *   }
+   * }
+   */
+  class ThreadHangStatsIterator : public MonitorAutoLock
+  {
+  private:
+    BackgroundHangThread* mThread;
+
+    ThreadHangStatsIterator(const ThreadHangStatsIterator&);
+    ThreadHangStatsIterator& operator=(const ThreadHangStatsIterator&);
+
+  public:
+    /**
+     * Create an ThreadHangStatsIterator instance and take the internal lock.
+     * Internal lock is released on destruction.
+     */
+    ThreadHangStatsIterator();
+
+    /**
+     * Get the next item in the list; the first call returns the first item.
+     * Returns nullptr at the end of the list.
+     */
+    Telemetry::ThreadHangStats* GetNext();
+  };
+
   /**
    * Enable hang monitoring.
    * Must return before using BackgroundHangMonitor.