core: reserve vector sizes as much as we can (#9118)

avoid reallocations as much as possible with a few edge cases where the
reservation overshoots a tiny bit. but a few bytes of memory short term
is better used then the overhead of potential reallocation.

4 files changed, 20 insertions, 2 deletions

diff --git a/src/protocols/DRMLease.cpp b/src/protocols/DRMLease.cpp
index fce1e345..6fdbaf4b 100644
--- a/src/protocols/DRMLease.cpp
+++ b/src/protocols/DRMLease.cpp
@@ -34,6 +34,9 @@ CDRMLeaseResource::CDRMLeaseResource(SP<CWpDrmLeaseV1> resource_, SP<CDRMLeaseRe
     }());
 
     std::vector<SP<Aquamarine::IOutput>> outputs;
+    // reserve to avoid reallocations
+    outputs.reserve(requested.size());
+
     for (auto const& m : requested) {
         outputs.emplace_back(m->monitor->output);
     }
diff --git a/src/protocols/GlobalShortcuts.cpp b/src/protocols/GlobalShortcuts.cpp
index 6fac2d7f..9f8f422c 100644
--- a/src/protocols/GlobalShortcuts.cpp
+++ b/src/protocols/GlobalShortcuts.cpp
@@ -83,8 +83,19 @@ void CGlobalShortcutsProtocol::sendGlobalShortcutEvent(std::string appid, std::s
 
 std::vector<SShortcut> CGlobalShortcutsProtocol::getAllShortcuts() {
     std::vector<SShortcut> copy;
-    for (auto const& c : m_vClients) {
-        for (auto const& sh : c->shortcuts) {
+    // calculate the total number of shortcuts, precomputing size is linear
+    // and potential reallocation is more costly then the added precompute overhead of looping
+    // and finding the total size.
+    size_t totalShortcuts = 0;
+    for (const auto& c : m_vClients) {
+        totalShortcuts += c->shortcuts.size();
+    }
+
+    // reserve number of elements to avoid reallocations
+    copy.reserve(totalShortcuts);
+
+    for (const auto& c : m_vClients) {
+        for (const auto& sh : c->shortcuts) {
             copy.push_back(*sh);
         }
     }
diff --git a/src/protocols/Screencopy.cpp b/src/protocols/Screencopy.cpp
index 8bdaf8f9..5cf54eb4 100644
--- a/src/protocols/Screencopy.cpp
+++ b/src/protocols/Screencopy.cpp
@@ -412,6 +412,8 @@ void CScreencopyProtocol::onOutputCommit(PHLMONITOR pMonitor) {
     }
 
     std::vector<WP<CScreencopyFrame>> framesToRemove;
+    // reserve number of elements to avoid reallocations
+    framesToRemove.reserve(m_vFramesAwaitingWrite.size());
 
     // share frame if correct output
     for (auto const& f : m_vFramesAwaitingWrite) {
diff --git a/src/protocols/ToplevelExport.cpp b/src/protocols/ToplevelExport.cpp
index 2d40cb78..fb49f722 100644
--- a/src/protocols/ToplevelExport.cpp
+++ b/src/protocols/ToplevelExport.cpp
@@ -393,6 +393,8 @@ void CToplevelExportProtocol::onOutputCommit(PHLMONITOR pMonitor) {
         return; // nothing to share
 
     std::vector<WP<CToplevelExportFrame>> framesToRemove;
+    // reserve number of elements to avoid reallocations
+    framesToRemove.reserve(m_vFramesAwaitingWrite.size());
 
     // share frame if correct output
     for (auto const& f : m_vFramesAwaitingWrite) {