[OutputBackend] Virtualize LoadedModuleTraceFile

Virtualize LoadedModuleTraceFile output using the new appending support
in virtual output backend.

Author: cachemeifyoucan

lib/FrontendTool/LoadedModuleTrace.cpp

@@ -780,70 +780,25 @@ bool swift::emitLoadedModuleTraceIfNeeded(ModuleDecl *mainModule,
   }
   stringBuffer += "\n";
 
-  // If writing to stdout, just perform a normal write.
-  // If writing to a file, ensure the write is atomic by creating a filesystem lock
-  // on the output file path.
-  std::error_code EC;
-  if (loadedModuleTracePath == "-") {
-    llvm::raw_fd_ostream out(loadedModuleTracePath, EC, llvm::sys::fs::OF_Append);
-    if (out.has_error() || EC) {
-      ctxt.Diags.diagnose(SourceLoc(), diag::error_opening_output,
-                          loadedModuleTracePath, EC.message());
-      out.clear_error();
-      return true;
-    }
-    out << stringBuffer;
-  } else {
-    while (1) {
-      // Attempt to lock the output file.
-      // Only one process is allowed to append to this file at a time.
-      llvm::LockFileManager Locked(loadedModuleTracePath);
-      switch (Locked) {
-        case llvm::LockFileManager::LFS_Error:{
-          // If we error acquiring a lock, we cannot ensure appends
-          // to the trace file are atomic - cannot ensure output correctness.
-          ctxt.Diags.diagnose(SourceLoc(), diag::error_opening_output,
-                              loadedModuleTracePath,
-                              "Failed to acquire filesystem lock");
-          Locked.unsafeRemoveLockFile();
-          return true;
-        }
-        case llvm::LockFileManager::LFS_Owned: {
-          // Lock acquired, perform the write and release the lock.
-          llvm::raw_fd_ostream out(loadedModuleTracePath, EC, llvm::sys::fs::OF_Append);
-          if (out.has_error() || EC) {
-            ctxt.Diags.diagnose(SourceLoc(), diag::error_opening_output,
-                                loadedModuleTracePath, EC.message());
-            out.clear_error();
-            return true;
-          }
-          out << stringBuffer;
-          out.close();
-          Locked.unsafeRemoveLockFile();
-          return false;
-        }
-        case llvm::LockFileManager::LFS_Shared: {
-          // Someone else owns the lock on this file, wait.
-          switch (Locked.waitForUnlock(256)) {
-            case llvm::LockFileManager::Res_Success:
-              LLVM_FALLTHROUGH;
-            case llvm::LockFileManager::Res_OwnerDied: {
-              continue; // try again to get the lock.
-            }
-            case llvm::LockFileManager::Res_Timeout: {
-              // We could error on timeout to avoid potentially hanging forever, but
-              // it may be more likely that an interrupted process failed to clear the lock,
-              // causing other waiting processes to time-out. Let's clear the lock and try
-              // again right away. If we do start seeing compiler hangs in this location,
-              // we will need to re-consider.
-              Locked.unsafeRemoveLockFile();
-              continue;
-            }
-          }
-          break;
-        }
-      }
-    }
+  // Write output via atomic append.
+  llvm::vfs::OutputConfig config;
+  config.setAppend().setAtomicWrite();
+  auto outputFile =
+      ctxt.getOutputBackend().createFile(loadedModuleTracePath, config);
+
+  if (!outputFile) {
+    ctxt.Diags.diagnose(SourceLoc(), diag::error_opening_output,
+                        loadedModuleTracePath,
+                        toString(outputFile.takeError()));
+    return true;
+  }
+
+  *outputFile << stringBuffer;
+
+  if (auto err = outputFile->keep()) {
+    ctxt.Diags.diagnose(SourceLoc(), diag::error_opening_output,
+                        loadedModuleTracePath, toString(std::move(err)));
+    return true;
   }
-  return true;
+  return false;
 }

test/Frontend/output_determinism_check.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: echo '[]' > %t/protocol.json
-// RUN: %target-swift-frontend -module-name test -emit-module -o %t/test.swiftmodule %s -emit-module-doc-path %t/test.docc -const-gather-protocols-file %t/protocol.json -emit-const-values-path %t/test.swiftconstvalues -emit-tbd-path %t/test.tbd -tbd-current-version 1 -tbd-compatibility-version 1 -tbd-install_name @rpath/test.dylib -enable-deterministic-check 2>&1 | %FileCheck %s --check-prefix=MODULE_OUTPUT --check-prefix=DOCC_OUTPUT --check-prefix=CONSTVALUE_OUTPUT --check-prefix=TBD_OUTPUT
+// RUN: %target-swift-frontend -module-name test -emit-module -o %t/test.swiftmodule %s -emit-module-doc-path %t/test.docc -const-gather-protocols-file %t/protocol.json -emit-const-values-path %t/test.swiftconstvalues -emit-tbd-path %t/test.tbd -tbd-current-version 1 -tbd-compatibility-version 1 -tbd-install_name @rpath/test.dylib -emit-loaded-module-trace -emit-loaded-module-trace-path %t/test.trace.json -enable-deterministic-check 2>&1 | %FileCheck %s --check-prefix=MODULE_OUTPUT --check-prefix=DOCC_OUTPUT --check-prefix=CONSTVALUE_OUTPUT --check-prefix=TBD_OUTPUT --check-prefix=TRACE_OUTPUT
 // RUN: %target-swift-frontend -module-name test -emit-sib -o %t/test.sib -primary-file %s -enable-deterministic-check 2>&1 | %FileCheck %s --check-prefix=SIB_OUTPUT
 
 /// object files are "not" deterministic because the second run going to match the mod hash and skip code generation.
@@ -29,6 +29,7 @@
 // CONSTVALUE_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.swiftconstvalues'
 // MODULE_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.swiftmodule'
 // TBD_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.tbd'
+// TRACE_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.trace.json'
 // SIB_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.sib'
 // DEPS_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.d'
 // OBJECT_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.o'