Commit 8e0f203a authored by Igor Kushnir's avatar Igor Kushnir
Browse files

ProjectFileDataProvider::projectClosing: match projectPath

The current algorithm iterates over project files and erases matching
items from QVector m_projectFiles one by one. This is very slow, because
KDevelop::forEachFile() iterates over project files in an order close to
lexicographic, and m_projectFiles is sorted in lexicographic order too.
So the average position of an erased item is close to QVector::begin().
The overall complexity of this algorithm is O(N*M), where N is the size
of m_projectFiles before a project is closed, and M is the number of
files in the project that is being closed.

Simply iterating over the project files in the reverse order speeds up
the erase one-by-one algorithm a lot. But there is an even faster
alternative, which is implemented in this commit: instead of iterating
over or collecting project files and then removing matching items from
m_projectFiles, remove all items that have projectPath equal to the path
of the project that is being closed. The complexity of this algorithm is

Before this commit on average 3150 ms were spent in
ProjectFileDataProvider::projectClosing() during KDevelop exit while a
single project - kdevelop itself with a little more than 67 thousand
files - was open. At this commit the time is just 14 ms. When the single
project to be closed was WebKit with its almost 320 thousand files,
about 196 *seconds* were spent in this function before the commit and
only 56 ms at this commit.

The best time I could achieve for closing kdevelop project by iterating
over project files in the reverse order and applying minor heuristic
optimizations was 165 ms. And such a reverse iteration could still be
extremely slow when several projects were closed.

This change makes
BenchQuickOpen::benchProjectFileFilter_addRemoveProject() 1.5 times
faster for a project with 100 files; 1.7 times faster for a project with
500 files; 2.2 times faster for a project with 1000 files; 5.9 times
faster for a project with 10000 files.

This commit changes behavior in case when a single file belongs to
multiple projects. Previously all files belonging to the project being
closed were removed. Now only the files that were added in the matching
projectOpened() call are removed. Neither the previous nor the current
behavior is ideal. But removing the files that were added along with the
project makes a bit more sense to me.

CCBUG: 427481
parent ae1aa195
......@@ -244,9 +244,12 @@ void ProjectFileDataProvider::projectClosing(IProject* project)
// file additions to the project that is about to be closed and destroyed.
disconnect(project, nullptr, this, nullptr);
KDevelop::forEachFile(project->projectItem(), [this](ProjectFileItem* file) {
const Path projectPath = project->path();
const auto logicalEnd = std::remove_if(m_projectFiles.begin(), m_projectFiles.end(),
[&projectPath](const ProjectFile& f) {
return f.projectPath == projectPath;
m_projectFiles.erase(logicalEnd, m_projectFiles.end());
void ProjectFileDataProvider::projectOpened(IProject* project)
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