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[clangd] Extract per-dir CDB cache to its own threadsafe class. NFC

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This is a step towards making compile_commands.json reloadable.

The idea is:
 - in addition to rare CDB loads we're soon going to have somewhat-rare CDB
   reloads and fairly-common stat() of files to validate the CDB
 - so stop doing all our work under a big global lock, instead using it to
   acquire per-directory structures with their own locks
 - each directory can be refreshed from disk every N seconds, like filecache
 - avoid locking these at all in the most common case: directory has no CDB

Differential Revision: https://reviews.llvm.org/D92381
This commit is contained in:
Sam McCall 2020-12-01 12:48:41 +01:00
parent 717b0da7a6
commit 634a377bd8
2 changed files with 190 additions and 89 deletions
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249
clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
View File

@ -16,11 +16,13 @@
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/FileUtilities.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Program.h"
#include <chrono>
#include <string>
#include <tuple>
#include <vector>
@ -58,10 +60,117 @@ GlobalCompilationDatabase::getFallbackCommand(PathRef File) const {
return Cmd;
}
// Loads and caches the CDB from a single directory.
//
// This class is threadsafe, which is to say we have independent locks for each
// directory we're searching for a CDB.
// Loading is deferred until first access.
//
// The DirectoryBasedCDB keeps a map from path => DirectoryCache.
// Typical usage is to:
// - 1) determine all the paths that might be searched
// - 2) acquire the map lock and get-or-create all the DirectoryCache entries
// - 3) release the map lock and query the caches as desired
//
// FIXME: this should revalidate the cache sometimes
// FIXME: IO should go through a VFS
class DirectoryBasedGlobalCompilationDatabase::DirectoryCache {
// Absolute canonical path that we're the cache for. (Not case-folded).
const std::string Path;
// True if we've looked for a CDB here and found none.
// (This makes it possible for get() to return without taking a lock)
// FIXME: this should have an expiry time instead of lasting forever.
std::atomic<bool> FinalizedNoCDB = {false};
// Guards following cache state.
std::mutex Mu;
// Has cache been filled from disk? FIXME: this should be an expiry time.
bool CachePopulated = false;
// Whether a new CDB has been loaded but not broadcast yet.
bool NeedsBroadcast = false;
// Last loaded CDB, meaningful if CachePopulated is set.
// shared_ptr so we can overwrite this when callers are still using the CDB.
std::shared_ptr<tooling::CompilationDatabase> CDB;
public:
DirectoryCache(llvm::StringRef Path) : Path(Path) {
assert(llvm::sys::path::is_absolute(Path));
}
// Get the CDB associated with this directory.
// ShouldBroadcast:
// - as input, signals whether the caller is willing to broadcast a
// newly-discovered CDB. (e.g. to trigger background indexing)
// - as output, signals whether the caller should do so.
// (If a new CDB is discovered and ShouldBroadcast is false, we mark the
// CDB as needing broadcast, and broadcast it next time we can).
std::shared_ptr<const tooling::CompilationDatabase>
get(bool &ShouldBroadcast) {
// Fast path for common case without taking lock.
if (FinalizedNoCDB.load()) {
ShouldBroadcast = false;
return nullptr;
}
std::lock_guard<std::mutex> Lock(Mu);
auto RequestBroadcast = llvm::make_scope_exit([&, OldCDB(CDB.get())] {
// If we loaded a new CDB, it should be broadcast at some point.
if (CDB != nullptr && CDB.get() != OldCDB)
NeedsBroadcast = true;
else if (CDB == nullptr) // nothing to broadcast anymore!
NeedsBroadcast = false;
// If we have something to broadcast, then do so iff allowed.
if (!ShouldBroadcast)
return;
ShouldBroadcast = NeedsBroadcast;
NeedsBroadcast = false;
});
// For now, we never actually attempt to revalidate a populated cache.
if (CachePopulated)
return CDB;
assert(CDB == nullptr);
load();
CachePopulated = true;
if (!CDB)
FinalizedNoCDB.store(true);
return CDB;
}
llvm::StringRef path() const { return Path; }
private:
// Updates `CDB` from disk state.
void load() {
std::string Error; // ignored, because it's often "didn't find anything".
CDB = tooling::CompilationDatabase::loadFromDirectory(Path, Error);
if (!CDB) {
// Fallback: check for $src/build, the conventional CMake build root.
// Probe existence first to avoid each plugin doing IO if it doesn't
// exist.
llvm::SmallString<256> BuildDir(Path);
llvm::sys::path::append(BuildDir, "build");
if (llvm::sys::fs::is_directory(BuildDir)) {
vlog("Found candidate build directory {0}", BuildDir);
CDB = tooling::CompilationDatabase::loadFromDirectory(BuildDir, Error);
}
}
if (CDB) {
log("Loaded compilation database from {0}", Path);
} else {
vlog("No compilation database at {0}", Path);
}
}
};
DirectoryBasedGlobalCompilationDatabase::
DirectoryBasedGlobalCompilationDatabase(
llvm::Optional<Path> CompileCommandsDir)
: CompileCommandsDir(std::move(CompileCommandsDir)) {}
llvm::Optional<Path> CompileCommandsDir) {
if (CompileCommandsDir)
OnlyDirCache = std::make_unique<DirectoryCache>(*CompileCommandsDir);
}
DirectoryBasedGlobalCompilationDatabase::
~DirectoryBasedGlobalCompilationDatabase() = default;
@ -107,31 +216,21 @@ static bool pathEqual(PathRef A, PathRef B) {
#endif
}
DirectoryBasedGlobalCompilationDatabase::CachedCDB &
DirectoryBasedGlobalCompilationDatabase::getCDBInDirLocked(PathRef Dir) const {
// FIXME(ibiryukov): Invalidate cached compilation databases on changes
auto Key = maybeCaseFoldPath(Dir);
auto R = CompilationDatabases.try_emplace(Key);
if (R.second) { // Cache miss, try to load CDB.
CachedCDB &Entry = R.first->second;
std::string Error;
Entry.Path = std::string(Dir);
Entry.CDB = tooling::CompilationDatabase::loadFromDirectory(Dir, Error);
// Check for $src/build, the conventional CMake build root.
// Probe existence first to avoid each plugin doing IO if it doesn't exist.
if (!CompileCommandsDir && !Entry.CDB) {
llvm::SmallString<256> BuildDir = Dir;
llvm::sys::path::append(BuildDir, "build");
if (llvm::sys::fs::is_directory(BuildDir)) {
vlog("Found candidate build directory {0}", BuildDir);
Entry.CDB =
tooling::CompilationDatabase::loadFromDirectory(BuildDir, Error);
}
}
if (Entry.CDB)
log("Loaded compilation database from {0}", Dir);
}
return R.first->second;
std::vector<DirectoryBasedGlobalCompilationDatabase::DirectoryCache *>
DirectoryBasedGlobalCompilationDatabase::getDirectoryCaches(
llvm::ArrayRef<llvm::StringRef> Dirs) const {
std::vector<std::string> FoldedDirs;
FoldedDirs.reserve(Dirs.size());
for (const auto &Dir : Dirs)
FoldedDirs.push_back(maybeCaseFoldPath(Dir));
std::vector<DirectoryCache *> Ret;
Ret.reserve(Dirs.size());
std::lock_guard<std::mutex> Lock(DirCachesMutex);
for (unsigned I = 0; I < Dirs.size(); ++I)
Ret.push_back(&DirCaches.try_emplace(FoldedDirs[I], Dirs[I]).first->second);
return Ret;
}
llvm::Optional<DirectoryBasedGlobalCompilationDatabase::CDBLookupResult>
@ -141,39 +240,40 @@ DirectoryBasedGlobalCompilationDatabase::lookupCDB(
"path must be absolute");
bool ShouldBroadcast = false;
CDBLookupResult Result;
{
std::lock_guard<std::mutex> Lock(Mutex);
CachedCDB *Entry = nullptr;
if (CompileCommandsDir) {
Entry = &getCDBInDirLocked(*CompileCommandsDir);
} else {
// Traverse the canonical version to prevent false positives. i.e.:
// src/build/../a.cc can detect a CDB in /src/build if not canonicalized.
// FIXME(sammccall): this loop is hot, use a union-find-like structure.
actOnAllParentDirectories(removeDots(Request.FileName),
[&](PathRef Path) {
Entry = &getCDBInDirLocked(Path);
return Entry->CDB != nullptr;
});
DirectoryCache *DirCache = nullptr;
std::shared_ptr<const tooling::CompilationDatabase> CDB = nullptr;
if (OnlyDirCache) {
DirCache = OnlyDirCache.get();
ShouldBroadcast = Request.ShouldBroadcast;
CDB = DirCache->get(ShouldBroadcast);
} else {
// Traverse the canonical version to prevent false positives. i.e.:
// src/build/../a.cc can detect a CDB in /src/build if not canonicalized.
std::string CanonicalPath = removeDots(Request.FileName);
std::vector<llvm::StringRef> SearchDirs;
actOnAllParentDirectories(CanonicalPath, [&](PathRef Path) {
SearchDirs.push_back(Path);
return false;
});
for (DirectoryCache *Candidate : getDirectoryCaches(SearchDirs)) {
bool CandidateShouldBroadcast = Request.ShouldBroadcast;
if ((CDB = Candidate->get(CandidateShouldBroadcast))) {
DirCache = Candidate;
ShouldBroadcast = CandidateShouldBroadcast;
break;
}
}
if (!Entry || !Entry->CDB)
return llvm::None;
// Mark CDB as broadcasted to make sure discovery is performed once.
if (Request.ShouldBroadcast && !Entry->SentBroadcast) {
Entry->SentBroadcast = true;
ShouldBroadcast = true;
}
Result.CDB = Entry->CDB.get();
Result.PI.SourceRoot = Entry->Path;
}
// FIXME: Maybe make the following part async, since this can block retrieval
// of compile commands.
if (!CDB)
return llvm::None;
CDBLookupResult Result;
Result.CDB = std::move(CDB);
Result.PI.SourceRoot = DirCache->path().str();
// FIXME: Maybe make the following part async, since this can block
// retrieval of compile commands.
if (ShouldBroadcast)
broadcastCDB(Result);
return Result;
@ -186,29 +286,32 @@ void DirectoryBasedGlobalCompilationDatabase::broadcastCDB(
std::vector<std::string> AllFiles = Result.CDB->getAllFiles();
// We assume CDB in CompileCommandsDir owns all of its entries, since we don't
// perform any search in parent paths whenever it is set.
if (CompileCommandsDir) {
assert(*CompileCommandsDir == Result.PI.SourceRoot &&
if (OnlyDirCache) {
assert(OnlyDirCache->path() == Result.PI.SourceRoot &&
"Trying to broadcast a CDB outside of CompileCommandsDir!");
OnCommandChanged.broadcast(std::move(AllFiles));
return;
}
// Uniquify all parent directories of all files.
llvm::StringMap<bool> DirectoryHasCDB;
{
std::lock_guard<std::mutex> Lock(Mutex);
// Uniquify all parent directories of all files.
for (llvm::StringRef File : AllFiles) {
actOnAllParentDirectories(File, [&](PathRef Path) {
auto It = DirectoryHasCDB.try_emplace(Path);
// Already seen this path, and all of its parents.
if (!It.second)
return true;
std::vector<llvm::StringRef> FileAncestors;
for (llvm::StringRef File : AllFiles) {
actOnAllParentDirectories(File, [&](PathRef Path) {
auto It = DirectoryHasCDB.try_emplace(Path);
// Already seen this path, and all of its parents.
if (!It.second)
return true;
CachedCDB &Entry = getCDBInDirLocked(Path);
It.first->second = Entry.CDB != nullptr;
return pathEqual(Path, Result.PI.SourceRoot);
});
}
FileAncestors.push_back(It.first->getKey());
return pathEqual(Path, Result.PI.SourceRoot);
});
}
// Work out which ones have CDBs in them.
for (DirectoryCache *Dir : getDirectoryCaches(FileAncestors)) {
bool ShouldBroadcast = false;
if (Dir->get(ShouldBroadcast))
DirectoryHasCDB.find(Dir->path())->setValue(true);
}
std::vector<std::string> GovernedFiles;

30
clang-tools-extra/clangd/GlobalCompilationDatabase.h
View File

@ -81,13 +81,19 @@ public:
llvm::Optional<ProjectInfo> getProjectInfo(PathRef File) const override;
private:
/// Caches compilation databases loaded from directories.
struct CachedCDB {
std::string Path; // Not case-folded.
std::unique_ptr<clang::tooling::CompilationDatabase> CDB = nullptr;
bool SentBroadcast = false;
};
CachedCDB &getCDBInDirLocked(PathRef File) const;
class DirectoryCache;
// If there's an explicit CompileCommandsDir, cache of the CDB found there.
mutable std::unique_ptr<DirectoryCache> OnlyDirCache;
// Keyed by possibly-case-folded directory path.
// We can hand out pointers as they're stable and entries are never removed.
// Empty if CompileCommandsDir is given (OnlyDirCache is used instead).
mutable llvm::StringMap<DirectoryCache> DirCaches;
// DirCaches access must be locked (unlike OnlyDirCache, which is threadsafe).
mutable std::mutex DirCachesMutex;
std::vector<DirectoryCache *>
getDirectoryCaches(llvm::ArrayRef<llvm::StringRef> Dirs) const;
struct CDBLookupRequest {
PathRef FileName;
@ -95,21 +101,13 @@ private:
bool ShouldBroadcast = false;
};
struct CDBLookupResult {
tooling::CompilationDatabase *CDB = nullptr;
std::shared_ptr<const tooling::CompilationDatabase> CDB;
ProjectInfo PI;
};
llvm::Optional<CDBLookupResult> lookupCDB(CDBLookupRequest Request) const;
// Performs broadcast on governed files.
void broadcastCDB(CDBLookupResult Res) const;
mutable std::mutex Mutex;
// Keyed by possibly-case-folded directory path.
mutable llvm::StringMap<CachedCDB> CompilationDatabases;
/// Used for command argument pointing to folder where compile_commands.json
/// is located.
llvm::Optional<Path> CompileCommandsDir;
};
/// Extracts system include search path from drivers matching QueryDriverGlobs