chore(hermetic-build): explore parallel generation

.dockerignore

@@ -0,0 +1,9 @@
+.git/
+.github/
+.kokoro/
+.vscode/
+bazel-*/
+googleapis/
+**/output/
+**/target/
+**/*.jar

sdk-platform-java/.cloudbuild/library_generation/cloudbuild-library-generation-integration-test.yaml

@@ -51,7 +51,7 @@ steps:
     cd /workspace
     git clone https://github.com/googleapis/google-cloud-java
     cd google-cloud-java
-    git checkout chore/test-hermetic-build
+    git checkout chore/test-hermetic-build-parallel
     mkdir ../golden
     cd ../golden
     cp -r ../google-cloud-java/java-apigee-connect .

sdk-platform-java/hermetic_build/library_generation/generate_composed_library.py

@@ -166,3 +166,18 @@ def _construct_effective_arg(
     arguments += ["--destination_path", temp_destination_path]
 
     return arguments
+
+
+import sys
+from io import StringIO
+import traceback
+
+
+def library_generation_worker(config, library_path, library, repo_config):
+    error_msg = None
+    try:
+        generate_composed_library(config, library_path, library, repo_config)
+    except Exception as e:
+        error_msg = f"{e}\n{traceback.format_exc()}"
+
+    return "", error_msg

sdk-platform-java/hermetic_build/library_generation/generate_library.sh

@@ -115,7 +115,9 @@ if [ -z "${artifact}" ]; then
   artifact=""
 fi
 
-temp_destination_path="${output_folder}/temp_preprocessed-$RANDOM"
+# Use mktemp to guarantee collision-free unique directories when multiple 
+# library generation processes run concurrently in a shared output folder
+temp_destination_path=$(mktemp -d -p "${output_folder}" temp_preprocessed-XXXXXX)
 mkdir -p "${output_folder}/${destination_path}"
 if [ -d "${temp_destination_path}" ]; then
   # we don't want the preprocessed sources of a previous run

sdk-platform-java/hermetic_build/library_generation/generate_repo.py

@@ -20,7 +20,10 @@
 from common.model.generation_config import GenerationConfig
 from common.model.library_config import LibraryConfig
 from common.utils.proto_path_utils import ends_with_version
-from library_generation.generate_composed_library import generate_composed_library
+from library_generation.generate_composed_library import (
+    generate_composed_library,
+    library_generation_worker,
+)
 from library_generation.utils.monorepo_postprocessor import monorepo_postprocessing
 
 from common.model.gapic_config import GapicConfig
@@ -57,14 +60,9 @@ def generate_from_yaml(
     )
     # copy api definition to output folder.
     shutil.copytree(api_definitions_path, repo_config.output_folder, dirs_exist_ok=True)
-    for library_path, library in repo_config.get_libraries().items():
-        print(f"generating library {library.get_library_name()}")
-        generate_composed_library(
-            config=config,
-            library_path=library_path,
-            library=library,
-            repo_config=repo_config,
-        )
+    _generate_libraries_in_parallel(config, repo_config)
+    sys.stdout = original_stdout
+    sys.stderr = original_stderr
 
     if not config.is_monorepo() or config.contains_common_protos():
         return
@@ -152,3 +150,72 @@ def _get_target_libraries_from_api_path(
             target_libraries.append(target_library)
             return target_libraries
     return []
+
+
+import os
+import sys
+import threading
+from concurrent.futures import ThreadPoolExecutor, as_completed
+
+
+class ThreadLocalStream:
+    """
+    Thread-safe interceptor to route print() statements into thread-local buffers.
+    Necessary because sys.stdout is a global stream; direct threading writes interleave outputs.
+    """
+
+    def __init__(self, original_stream):
+        self.original_stream = original_stream
+        self.local = threading.local()
+
+    @property
+    def buffer(self):
+        return getattr(self.local, "buffer", None)
+
+    def write(self, data):
+        writer = self.buffer if self.buffer is not None else self.original_stream
+        writer.write(data)
+
+    def flush(self):
+        if self.buffer is not None:
+            return
+        self.original_stream.flush()
+
+
+original_stdout, original_stderr = sys.stdout, sys.stderr
+
+print_lock = threading.Lock()
+
+
+def _print_worker_result(lib_name, logs, err):
+    """
+    Atomically prints the buffered output of a worker thread directly to original_stdout,
+    preventing output interleaving in the console.
+    """
+    print_lock.acquire()
+    status = "[FAILURE]" if err else "[SUCCESS]"
+    original_stdout.write(f"\n{'='*40}\n{status} Logs for {lib_name}:\n{'='*40}\n")
+    original_stdout.write(logs)
+    if err:
+        original_stdout.write(f"\nError details:\n{err}\n")
+    original_stdout.flush()
+    print_lock.release()
+
+
+def _generate_libraries_in_parallel(config, repo_config):
+    cores = os.cpu_count() or 4
+    executor = ThreadPoolExecutor(max_workers=min(cores, 5))
+
+    futures = {
+        executor.submit(
+            library_generation_worker, config, path, lib, repo_config
+        ): lib.get_library_name()
+        for path, lib in repo_config.get_libraries().items()
+    }
+
+    for future in as_completed(futures):
+        lib_name = futures[future]
+        logs, err = future.result()
+        _print_worker_result(lib_name, logs, err)
+
+    executor.shutdown()

sdk-platform-java/hermetic_build/library_generation/owlbot/bin/entrypoint.sh

@@ -60,7 +60,9 @@ echo "...done"
 
 # write or restore pom.xml files
 echo "Generating missing pom.xml..."
-python3 "${scripts_root}/owlbot/src/fix_poms.py" "${versions_file}" "${is_monorepo}"
+# Under parallel multi-library generation, fix_poms.py modifies the shared versions_file.
+# We use flock to serialize edits safely across concurrent processes.
+flock "${versions_file}" python3 "${scripts_root}/owlbot/src/fix_poms.py" "${versions_file}" "${is_monorepo}"
 echo "...done"
 
 # write or restore clirr-ignored-differences.xml