[clangd] Cleanup: make diagnostics callbacks from TUScheduler non-racy

Summary:
Previously, removeDoc followed by an addDoc to TUScheduler resulted in
racy diagnostic responses, i.e. the old dianostics could be delivered
to the client after the new ones by TUScheduler.

To workaround this, we tracked a version number in ClangdServer and
discarded stale diagnostics. After this commit, the TUScheduler will
stop delivering diagnostics for removed files and the workaround in
ClangdServer is not required anymore.

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: javed.absar, ioeric, MaskRay, jkorous, arphaman, jfb, kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D54829

llvm-svn: 347468

clang-tools-extra/clangd/ClangdServer.cpp

@@ -133,19 +133,17 @@ ClangdServer::ClangdServer(const GlobalCompilationDatabase &CDB,
 
 void ClangdServer::addDocument(PathRef File, StringRef Contents,
                                WantDiagnostics WantDiags) {
-  DocVersion Version = ++InternalVersion[File];
   ParseInputs Inputs = {getCompileCommand(File), FSProvider.getFileSystem(),
                         Contents.str()};
-
   Path FileStr = File.str();
   WorkScheduler.update(File, std::move(Inputs), WantDiags,
-                       [this, FileStr, Version](std::vector<Diag> Diags) {
+                       [this, FileStr](std::vector<Diag> Diags) {
-                         consumeDiagnostics(FileStr, Version, std::move(Diags));
+                         DiagConsumer.onDiagnosticsReady(FileStr,
+                                                         std::move(Diags));
                        });
 }
 
 void ClangdServer::removeDocument(PathRef File) {
-  ++InternalVersion[File];
   WorkScheduler.remove(File);
 }
 
@@ -444,24 +442,6 @@ void ClangdServer::findHover(PathRef File, Position Pos,
   WorkScheduler.runWithAST("Hover", File, Bind(Action, std::move(CB)));
 }
 
-void ClangdServer::consumeDiagnostics(PathRef File, DocVersion Version,
-                                      std::vector<Diag> Diags) {
-  // We need to serialize access to resulting diagnostics to avoid calling
-  // `onDiagnosticsReady` in the wrong order.
-  std::lock_guard<std::mutex> DiagsLock(DiagnosticsMutex);
-  DocVersion &LastReportedDiagsVersion = ReportedDiagnosticVersions[File];
-
-  // FIXME(ibiryukov): get rid of '<' comparison here. In the current
-  // implementation diagnostics will not be reported after version counters'
-  // overflow. This should not happen in practice, since DocVersion is a
-  // 64-bit unsigned integer.
-  if (Version < LastReportedDiagsVersion)
-    return;
-  LastReportedDiagsVersion = Version;
-
-  DiagConsumer.onDiagnosticsReady(File, std::move(Diags));
-}
-
 tooling::CompileCommand ClangdServer::getCompileCommand(PathRef File) {
   trace::Span Span("GetCompileCommand");
   Optional<tooling::CompileCommand> C = CDB.getCompileCommand(File);

clang-tools-extra/clangd/ClangdServer.h

@@ -125,7 +125,8 @@ public:
                    WantDiagnostics WD = WantDiagnostics::Auto);
 
   /// Remove \p File from list of tracked files, schedule a request to free
-  /// resources associated with it.
+  /// resources associated with it. Pending diagnostics for closed files may not
+  /// be delivered, even if requested with WantDiags::Auto or WantDiags::Yes.
   void removeDocument(PathRef File);
 
   /// Run code completion for \p File at \p Pos.
@@ -222,20 +223,12 @@ private:
   formatCode(llvm::StringRef Code, PathRef File,
              ArrayRef<tooling::Range> Ranges);
 
-  typedef uint64_t DocVersion;
-
-  void consumeDiagnostics(PathRef File, DocVersion Version,
-                          std::vector<Diag> Diags);
-
   tooling::CompileCommand getCompileCommand(PathRef File);
 
   const GlobalCompilationDatabase &CDB;
   DiagnosticsConsumer &DiagConsumer;
   const FileSystemProvider &FSProvider;
 
-  /// Used to synchronize diagnostic responses for added and removed files.
-  llvm::StringMap<DocVersion> InternalVersion;
-
   Path ResourceDir;
   // The index used to look up symbols. This could be:
   //   - null (all index functionality is optional)
@@ -255,12 +248,6 @@ private:
 
   llvm::Optional<std::string> WorkspaceRoot;
   std::shared_ptr<PCHContainerOperations> PCHs;
-  /// Used to serialize diagnostic callbacks.
-  /// FIXME(ibiryukov): get rid of an extra map and put all version counters
-  /// into CppFile.
-  std::mutex DiagnosticsMutex;
-  /// Maps from a filename to the latest version of reported diagnostics.
-  llvm::StringMap<DocVersion> ReportedDiagnosticVersions;
   // WorkScheduler has to be the last member, because its destructor has to be
   // called before all other members to stop the worker thread that references
   // ClangdServer.

clang-tools-extra/clangd/TUScheduler.cpp

@@ -252,6 +252,13 @@ private:
   bool Done;                    /* GUARDED_BY(Mutex) */
   std::deque<Request> Requests; /* GUARDED_BY(Mutex) */
   mutable std::condition_variable RequestsCV;
+  /// Guards a critical section for running the diagnostics callbacks. 
+  std::mutex DiagsMu;
+  // Used to prevent remove document + leading to out-of-order diagnostics:
+  // The lifetime of the old/new ASTWorkers will overlap, but their handles
+  // don't. When the old handle is destroyed, the old worker will stop reporting
+  // diagnostics.
+  bool ReportDiagnostics = true; /* GUARDED_BY(DiagMu) */
 };
 
 /// A smart-pointer-like class that points to an active ASTWorker.
@@ -406,6 +413,14 @@ void ASTWorker::update(ParseInputs Inputs, WantDiagnostics WantDiags,
     if (WantDiags == WantDiagnostics::No)
       return;
 
+    {
+      std::lock_guard<std::mutex> Lock(DiagsMu);
+      // No need to rebuild the AST if we won't send the diagnotics. However,
+      // note that we don't prevent preamble rebuilds.
+      if (!ReportDiagnostics)
+        return;
+    }
+
     // Get the AST for diagnostics.
     Optional<std::unique_ptr<ParsedAST>> AST = IdleASTs.take(this);
     if (!AST) {
@@ -418,7 +433,11 @@ void ASTWorker::update(ParseInputs Inputs, WantDiagnostics WantDiags,
     // spam us with updates.
     // Note *AST can still be null if buildAST fails.
     if (*AST) {
-      OnUpdated((*AST)->getDiagnostics());
+      {
+        std::lock_guard<std::mutex> Lock(DiagsMu);
+        if (ReportDiagnostics)
+          OnUpdated((*AST)->getDiagnostics());
+      }
       trace::Span Span("Running main AST callback");
       Callbacks.onMainAST(FileName, **AST);
       DiagsWereReported = true;
@@ -512,6 +531,10 @@ std::size_t ASTWorker::getUsedBytes() const {
 bool ASTWorker::isASTCached() const { return IdleASTs.getUsedBytes(this) != 0; }
 
 void ASTWorker::stop() {
+  {
+    std::lock_guard<std::mutex> Lock(DiagsMu);
+    ReportDiagnostics = false;
+  }
   {
     std::lock_guard<std::mutex> Lock(Mutex);
     assert(!Done && "stop() called twice");

clang-tools-extra/clangd/TUScheduler.h

@@ -108,7 +108,8 @@ public:
               llvm::unique_function<void(std::vector<Diag>)> OnUpdated);
 
   /// Remove \p File from the list of tracked files and schedule removal of its
-  /// resources.
+  /// resources. Pending diagnostics for closed files may not be delivered, even
+  /// if requested with WantDiags::Auto or WantDiags::Yes.
   void remove(PathRef File);
 
   /// Schedule an async task with no dependencies.

clang-tools-extra/unittests/clangd/ClangdTests.cpp

@@ -748,7 +748,8 @@ int d;
         BlockingRequests[RequestIndex]();
       }
     }
-  } // Wait for ClangdServer to shutdown before proceeding.
+    ASSERT_TRUE(Server.blockUntilIdleForTest());
+  }
 
   // Check some invariants about the state of the program.
   std::vector<FileStat> Stats = DiagConsumer.takeFileStats();

clang-tools-extra/unittests/clangd/TUSchedulerTests.cpp

@@ -124,6 +124,8 @@ TEST_F(TUSchedulerTests, WantDiagnostics) {
     S.update(Path, getInputs(Path, "auto (produces)"), WantDiagnostics::Auto,
              [&](std::vector<Diag> Diags) { ++CallbackCount; });
     Ready.notify();
+
+    ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
   }
   EXPECT_EQ(2, CallbackCount);
 }
@@ -147,6 +149,8 @@ TEST_F(TUSchedulerTests, Debounce) {
     std::this_thread::sleep_for(std::chrono::seconds(2));
     S.update(Path, getInputs(Path, "auto (shut down)"), WantDiagnostics::Auto,
              [&](std::vector<Diag> Diags) { ++CallbackCount; });
+
+    ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
   }
   EXPECT_EQ(2, CallbackCount);
 }
@@ -267,6 +271,8 @@ TEST_F(TUSchedulerTests, Cancellation) {
     Update("U3");
     Read("R3")();
     Proceed.notify();
+
+    ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
   }
   EXPECT_THAT(DiagsSeen, ElementsAre("U2", "U3"))
       << "U1 and all dependent reads were cancelled. "
@@ -373,6 +379,7 @@ TEST_F(TUSchedulerTests, ManyUpdates) {
         }
       }
     }
+    ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
   } // TUScheduler destructor waits for all operations to finish.
 
   std::lock_guard<std::mutex> Lock(Mut);