From 7e880fe1f8e155f7c354e95904d9df91e28c35fe Mon Sep 17 00:00:00 2001
From: Markus Stange <mstange@themasta.com>
Date: Tue, 6 Feb 2018 15:29:05 -0500
Subject: [PATCH] Bug 1431179 - Keep all exit profiles that overlap with the
 parent process's buffer time range. r=mconley

MozReview-Commit-ID: 1DIYQZ70ckR

--HG--
extra : rebase_source : f7f5e8e2d0380b54c50cb20b3d109cb476a2530f
extra : source : 612e54e7001a5907761d831b92aed5cee0deb017
---
 tools/profiler/gecko/nsProfiler.cpp | 46 +++++++++++++----------------
 tools/profiler/gecko/nsProfiler.h   |  3 ++
 2 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/tools/profiler/gecko/nsProfiler.cpp b/tools/profiler/gecko/nsProfiler.cpp
index 6907c221b310..d8ba397d540a 100644
--- a/tools/profiler/gecko/nsProfiler.cpp
+++ b/tools/profiler/gecko/nsProfiler.cpp
@@ -539,12 +539,6 @@ nsProfiler::GatheredOOPProfile(const nsACString& aProfile)
   }
 }
 
-// When a subprocess exits before we've gathered profiles, we'll store profiles
-// for those processes until gathering starts. We'll only store up to
-// MAX_SUBPROCESS_EXIT_PROFILES. The buffer is circular, so as soon as we
-// receive another exit profile, we'll bump the oldest one out of the buffer.
-static const uint32_t MAX_SUBPROCESS_EXIT_PROFILES = 5;
-
 void
 nsProfiler::ReceiveShutdownProfile(const nsCString& aProfile)
 {
@@ -556,16 +550,14 @@ nsProfiler::ReceiveShutdownProfile(const nsCString& aProfile)
     return;
   }
 
-  // Append the exit profile to mExitProfiles so that it can be picked up the
-  // next time a profile is requested. If we're currently gathering a profile,
-  // do not add this exit profile to it; chances are that we already have a
-  // profile from the exiting process and we don't want another one.
-  // We only keep around at most MAX_SUBPROCESS_EXIT_PROFILES exit profiles.
-  if (mExitProfiles.Length() >= MAX_SUBPROCESS_EXIT_PROFILES) {
-    mExitProfiles.RemoveElementAt(0);
-  }
+  // Append the exit profile to mExitProfiles so that it can be picked up when
+  // a profile is requested.
   uint64_t bufferPosition = bufferInfo->mRangeEnd;
   mExitProfiles.AppendElement(ExitProfile{ aProfile, bufferPosition });
+
+  // This is a good time to clear out exit profiles whose time ranges have no
+  // overlap with this process's profile buffer contents any more.
+  ClearExpiredExitProfiles();
 }
 
 RefPtr<nsProfiler::GatheringPromise>
@@ -592,8 +584,6 @@ nsProfiler::StartGathering(double aSinceTime)
 
   mWriter.emplace();
 
-  Maybe<ProfilerBufferInfo> bufferInfo = profiler_get_buffer_info();
-
   // Start building up the JSON result and grab the profile from this process.
   mWriter->Start();
   if (!profiler_stream_json_for_this_process(*mWriter, aSinceTime,
@@ -607,20 +597,14 @@ nsProfiler::StartGathering(double aSinceTime)
 
   mWriter->StartArrayProperty("processes");
 
-  // If we have any process exit profiles, add them immediately, and clear
-  // mExitProfiles.
+  ClearExpiredExitProfiles();
+
+  // If we have any process exit profiles, add them immediately.
   for (auto& exitProfile : mExitProfiles) {
-    if (bufferInfo &&
-        exitProfile.mBufferPositionAtGatherTime < bufferInfo->mRangeStart) {
-      // Don't include exit profiles that have no overlap with the profile
-      // from our own process.
-      continue;
-    }
     if (!exitProfile.mJSON.IsEmpty()) {
       mWriter->Splice(exitProfile.mJSON.get());
     }
   }
-  mExitProfiles.Clear();
 
   mPromiseHolder.emplace();
   RefPtr<GatheringPromise> promise = mPromiseHolder->Ensure(__func__);
@@ -676,3 +660,15 @@ nsProfiler::ResetGathering()
   mGathering = false;
   mWriter.reset();
 }
+
+void
+nsProfiler::ClearExpiredExitProfiles()
+{
+  Maybe<ProfilerBufferInfo> bufferInfo = profiler_get_buffer_info();
+  MOZ_RELEASE_ASSERT(bufferInfo, "the profiler should be running at the moment");
+  uint64_t bufferRangeStart = bufferInfo->mRangeStart;
+  // Discard any exit profiles that were gathered before bufferRangeStart.
+  mExitProfiles.RemoveElementsBy([bufferRangeStart](ExitProfile& aExitProfile){
+    return aExitProfile.mBufferPositionAtGatherTime < bufferRangeStart;
+  });
+}
\ No newline at end of file
diff --git a/tools/profiler/gecko/nsProfiler.h b/tools/profiler/gecko/nsProfiler.h
index 4dcb9ebba19f..a530f09417cc 100644
--- a/tools/profiler/gecko/nsProfiler.h
+++ b/tools/profiler/gecko/nsProfiler.h
@@ -12,6 +12,7 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/MozPromise.h"
+#include "mozilla/TimeStamp.h"
 #include "nsServiceManagerUtils.h"
 #include "ProfileJSONWriter.h"
 
@@ -44,6 +45,8 @@ private:
   void FinishGathering();
   void ResetGathering();
 
+  void ClearExpiredExitProfiles();
+
   bool mLockedForPrivateBrowsing;
 
   struct ExitProfile {