Allow integers in parallel-fuzzing to force the number of cores

infra/cifuzz/actions/run_fuzzers/action.yml

@@ -45,7 +45,7 @@ inputs:
     required: false
     default: False
   parallel-fuzzing:
-    description: "Whether to use all available cores for fuzzing."
+    description: "How many cores to use cores for fuzzing. A specific number, True - all available cores or False to run single threaded on a single core."
     required: false
     default: false
   output-sarif:

infra/cifuzz/config_utils.py

@@ -129,7 +129,7 @@ def __init__(self):
     self.build_integration_path = (
         constants.DEFAULT_EXTERNAL_BUILD_INTEGRATION_PATH)
 
-    self.parallel_fuzzing = environment.get_bool('PARALLEL_FUZZING', False)
+    self.parallel_fuzzing = environment.get('PARALLEL_FUZZING', False)
     self.extra_environment_variables = _get_extra_environment_variables()
     self.output_sarif = environment.get_bool('OUTPUT_SARIF', False)
 

infra/cifuzz/external-actions/run_fuzzers/action.yml

@@ -57,7 +57,7 @@ inputs:
     required: false
     default: False
   parallel-fuzzing:
-    description: "Whether to use all available cores for fuzzing."
+    description: "How many cores to use cores for fuzzing. A specific number, True - all available cores or False to run single threaded on a single core."
     required: false
     default: false
   output-sarif:

infra/cifuzz/fuzz_target.py

@@ -57,10 +57,13 @@
                                     ['testcase', 'stacktrace', 'corpus_path'])
 
 
-def get_libfuzzer_parallel_options():
+def get_libfuzzer_parallel_options(option):
   """Returns a list containing options to pass to libFuzzer to fuzz using all
-  available cores."""
-  cpu_count = str(multiprocessing.cpu_count())
+  available or the specified number of cores."""
+  if option == 'true' or (isinstance(option, bool) and option == True):
+    cpu_count = str(multiprocessing.cpu_count())
+  else:
+    cpu_count = option
   return [f'-jobs={cpu_count}', f'-workers={cpu_count}']
 
 
@@ -190,13 +193,18 @@ def fuzz(self, batch=False) -> Optional[FuzzResult]:
         if not self.config.report_ooms:
           options.arguments.extend(LIBFUZZER_OPTIONS_NO_REPORT_OOM)
 
-        if self.config.parallel_fuzzing:
+        if (self.config.parallel_fuzzing == 'true' or
+            (isinstance(self.config.parallel_fuzzing, int) and
+             not isinstance(self.config.parallel_fuzzing, bool)) or
+            (isinstance(self.config.parallel_fuzzing, bool) and
+             self.config.parallel_fuzzing == True)):
           if self.config.sanitizer == 'memory':
             # TODO(https://github.com/google/oss-fuzz/issues/11915): Don't gate
             # this after jobs is fixed for MSAN.
             logging.info('Not using jobs because it breaks MSAN.')
           else:
-            options.arguments.extend(get_libfuzzer_parallel_options())
+            options.arguments.extend(
+                get_libfuzzer_parallel_options(self.config.parallel_fuzzing))
 
         result = engine_impl.fuzz(self.target_path, options, artifacts_dir,
                                   self.duration)