[Modules] In case of lock timeout, fallback and build module

Duncan's r298165 introduced the PCMCache mechanism, which guarantees
that locks aren't necessary anymore for correctness but only for
performance, by avoiding building it twice when possible.

Change the logic to avoid an error but actually build the module in case
the timeout happens. Instead of an error, still emit a remark for
debugging purposes.

rdar://problem/30297862

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@298175 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Basic/DiagnosticCommonKinds.td b/include/clang/Basic/DiagnosticCommonKinds.td
index b8293f08c523c7145628c776cf094668bd4fd901..98fd3c4d57ac0ba63bf2aa36f29fbb418aa1cb21 100644 (file)
--- a/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/include/clang/Basic/DiagnosticCommonKinds.td
@@ -90,10 +90,10 @@ def err_module_unavailable : Error<
   "module '%0' %select{is incompatible with|requires}1 feature '%2'">;
 def err_module_header_missing : Error<
   "%select{|umbrella }0header '%1' not found">;
-def err_module_lock_failure : Error<
-  "could not acquire lock file for module '%0': %1">, DefaultFatal;
-def err_module_lock_timeout : Error<
-  "timed out waiting to acquire lock file for module '%0'">, DefaultFatal;
+def remark_module_lock_failure : Remark<
+  "could not acquire lock file for module '%0': %1">, InGroup<ModuleBuild>;
+def remark_module_lock_timeout : Remark<
+  "timed out waiting to acquire lock file for module '%0'">, InGroup<ModuleBuild>;
 def err_module_cycle : Error<"cyclic dependency in module '%0': %1">, 
   DefaultFatal;
 def err_module_prebuilt : Error<

diff --git a/lib/Frontend/CompilerInstance.cpp b/lib/Frontend/CompilerInstance.cpp
index 4841c103f6195dfb7c83972f5957d649e0d719fc..f660429e49d688c18891fe2c78cd89a1473e898d 100644 (file)
--- a/lib/Frontend/CompilerInstance.cpp
+++ b/lib/Frontend/CompilerInstance.cpp
@@ -1190,10 +1190,14 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
     llvm::LockFileManager Locked(ModuleFileName);
     switch (Locked) {
     case llvm::LockFileManager::LFS_Error:
-      Diags.Report(ModuleNameLoc, diag::err_module_lock_failure)
+      // PCMCache takes care of correctness and locks are only necessary for
+      // performance. Fallback to building the module in case of any lock
+      // related errors.
+      Diags.Report(ModuleNameLoc, diag::remark_module_lock_failure)
           << Module->Name << Locked.getErrorMessage();
-      return false;
-
+      // Clear out any potential leftover.
+      Locked.unsafeRemoveLockFile();
+      // FALLTHROUGH
     case llvm::LockFileManager::LFS_Owned:
       // We're responsible for building the module ourselves.
       if (!compileModuleImpl(ImportingInstance, ModuleNameLoc, Module,
@@ -1213,11 +1217,14 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
       case llvm::LockFileManager::Res_OwnerDied:
         continue; // try again to get the lock.
       case llvm::LockFileManager::Res_Timeout:
-        Diags.Report(ModuleNameLoc, diag::err_module_lock_timeout)
+        // Since PCMCache takes care of correctness, we try waiting for another
+        // process to complete the build so clang does not do it done twice. If
+        // case of timeout, build it ourselves.
+        Diags.Report(ModuleNameLoc, diag::remark_module_lock_timeout)
             << Module->Name;
         // Clear the lock file so that future invokations can make progress.
         Locked.unsafeRemoveLockFile();
-        return false;
+        continue;
       }
       break;
     }