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authorDavid Teller <dteller@mozilla.com>2019-01-28 23:41:20 +0100
committerwolfbeast <mcwerewolf@wolfbeast.com>2019-01-28 23:41:20 +0100
commit3476c1d60ec29c5497123194acd7a9310b1023d2 (patch)
tree4933db7b4bb27893d3511ac21d5d04a11deea6a9 /toolkit/components/perfmonitoring/nsPerformanceStats.cpp
parente82fdef9c7bed415d004086740cab57211575511 (diff)
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Reduce number of allocations in AutoStopwatch
This patch fixes two related issues. 1. The AutoStopwatch uses a stack-allocated `mozilla::Vector` to communicate with its callback during each compartment switch. This vector was designed to allow its contents to be stack-allocated but they turned out to be accidentally heap-allocated. 2. During each tick, the stopwatch fills a vector `recentGroups_`. This vector always started with minimal capacity and had to grow repeatedly as groups were added, causing repeated reallocations. This patch preallocates `recentGroups_` to have the same capacity as the previous tick. We expect that this should eventually reach a stable size that closely matches the actual needs of the process.
Diffstat (limited to 'toolkit/components/perfmonitoring/nsPerformanceStats.cpp')
-rw-r--r--toolkit/components/perfmonitoring/nsPerformanceStats.cpp8
1 files changed, 6 insertions, 2 deletions
diff --git a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
index 6c470356a..03e63a461 100644
--- a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
+++ b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
@@ -1310,8 +1310,12 @@ nsPerformanceStatsService::GetResources(uint64_t* userTime,
void
nsPerformanceStatsService::NotifyJankObservers(const mozilla::Vector<uint64_t>& aPreviousJankLevels) {
- GroupVector alerts;
- mPendingAlerts.swap(alerts);
+
+ // The move operation is generally constant time, unless `mPendingAlerts.length()` is very small, in which case it's
+ // fast anyway.
+ GroupVector alerts(Move(mPendingAlerts));
+ mPendingAlerts = GroupVector(); // Reconstruct after `Move`.
+
if (!mPendingAlertsCollector) {
// We are shutting down.
return;