ci: run test round with parallel-checkout enabled

We already have tests for the basic parallel-checkout operations. But
this code can also run in other commands, such as git-read-tree and
git-sparse-checkout, which are currently not tested with multiple
workers. To promote a wider test coverage without duplicating tests:

1. Add the GIT_TEST_CHECKOUT_WORKERS environment variable, to optionally
   force parallel-checkout execution during the whole test suite.

2. Include this variable in the second test round of the linux-gcc job
   of our ci scripts. This round runs `make test` again with some
   optional GIT_TEST_* variables enabled, so there is no additional
   overhead in exercising the parallel-checkout code here.

Note: the specific parallel-checkout tests t208* cannot be used in
combination with GIT_TEST_CHECKOUT_WORKERS as they need to set and check
the number of workers by themselves. So skip those tests when this flag
is set.
Signed-off-by: NMatheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

ci/run-build-and-tests.sh

@@ -22,6 +22,7 @@ linux-gcc)
 	export GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=1
 	export GIT_TEST_MULTI_PACK_INDEX=1
 	export GIT_TEST_ADD_I_USE_BUILTIN=1
+	export GIT_TEST_CHECKOUT_WORKERS=2
 	make test
 	;;
 linux-clang)

parallel-checkout.c

@@ -32,6 +32,20 @@ enum pc_status parallel_checkout_status(void)
 
 void get_parallel_checkout_configs(int *num_workers, int *threshold)
 {
+	char *env_workers = getenv("GIT_TEST_CHECKOUT_WORKERS");
+
+	if (env_workers && *env_workers) {
+		if (strtol_i(env_workers, 10, num_workers)) {
+			die("invalid value for GIT_TEST_CHECKOUT_WORKERS: '%s'",
+			    env_workers);
+		}
+		if (*num_workers < 1)
+			*num_workers = online_cpus();
+
+		*threshold = 0;
+		return;
+	}
+
 	if (git_config_get_int("checkout.workers", num_workers))
 		*num_workers = 1;
 	else if (*num_workers < 1)

t/README

@@ -425,6 +425,10 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_CHECKOUT_WORKERS=<n> overrides the 'checkout.workers' setting
+to <n> and 'checkout.thresholdForParallelism' to 0, forcing the
+execution of the parallel-checkout code.
+
 Naming Tests
 ------------
 

t/lib-parallel-checkout.sh

 # Helpers for t208* tests
 
+if ! test -z "$GIT_TEST_CHECKOUT_WORKERS"
+then
+	skip_all="skipping test, GIT_TEST_CHECKOUT_WORKERS is set"
+	test_done
+fi
+
 # Runs `git -c checkout.workers=$1 -c checkout.thesholdForParallelism=$2 ${@:4}`
 # and checks that the number of workers spawned is equal to $3.
 git_pc()

t/t2081-parallel-checkout-collisions.sh

@@ -3,6 +3,7 @@
 test_description='parallel-checkout collisions'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY/lib-parallel-checkout.sh"
 
 # When there are pathname collisions during a clone, Git should report a warning
 # listing all of the colliding entries. The sequential code detects a collision