Re: [PATCH v2 5/8] parallel-checkout: add tests related to path collisions

> Add tests to confirm that path collisions are properly detected by
> checkout workers, both to avoid race conditions and to report colliding
> entries on clone.
>
> Co-authored-by: Jeff Hostetler <jeffhost@microsoft.com>
> Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
> ---
>  parallel-checkout.c                     |   4 +
>  t/lib-parallel-checkout.sh              |   4 +-
>  t/t2081-parallel-checkout-collisions.sh | 162 ++++++++++++++++++++++++
>  3 files changed, 168 insertions(+), 2 deletions(-)
>  create mode 100755 t/t2081-parallel-checkout-collisions.sh
>
> diff --git a/parallel-checkout.c b/parallel-checkout.c
> index 09e8b10a35..6fb3f1e6c9 100644
> --- a/parallel-checkout.c
> +++ b/parallel-checkout.c
> @@ -8,6 +8,7 @@
>  #include "sigchain.h"
>  #include "streaming.h"
>  #include "thread-utils.h"
> +#include "trace2.h"
>
>  struct pc_worker {
>  	struct child_process cp;
> @@ -326,6 +327,7 @@ void write_pc_item(struct parallel_checkout_item *pc_item,
>  	if (dir_sep && !has_dirs_only_path(path.buf, dir_sep - path.buf,
>  					   state->base_dir_len)) {
>  		pc_item->status = PC_ITEM_COLLIDED;
> +		trace2_data_string("pcheckout", NULL, "collision/dirname", path.buf);
>  		goto out;
>  	}
>
> @@ -341,6 +343,8 @@ void write_pc_item(struct parallel_checkout_item *pc_item,
>  			 * call should have already caught these cases.
>  			 */
>  			pc_item->status = PC_ITEM_COLLIDED;
> +			trace2_data_string("pcheckout", NULL,
> +					   "collision/basename", path.buf);
>  		} else {
>  			error_errno("failed to open file '%s'", path.buf);
>  			pc_item->status = PC_ITEM_FAILED;
> diff --git a/t/lib-parallel-checkout.sh b/t/lib-parallel-checkout.sh
> index f60b22ef34..d6740425b1 100644
> --- a/t/lib-parallel-checkout.sh
> +++ b/t/lib-parallel-checkout.sh
> @@ -22,12 +22,12 @@ test_checkout_workers () {
>
>  	local trace_file=trace-test-checkout-workers &&
>  	rm -f "$trace_file" &&
> -	GIT_TRACE2="$(pwd)/$trace_file" "$@" &&
> +	GIT_TRACE2="$(pwd)/$trace_file" "$@" 2>&8 &&
>
>  	local workers=$(grep "child_start\[..*\] git checkout--worker" "$trace_file" | wc -l) &&
>  	test $workers -eq $expected_workers &&
>  	rm "$trace_file"
> -}
> +} 8>&2 2>&4
>
>  # Verify that both the working tree and the index were created correctly
>  verify_checkout () {
> diff --git a/t/t2081-parallel-checkout-collisions.sh b/t/t2081-parallel-checkout-collisions.sh
> new file mode 100755
> index 0000000000..f6fcfc0c1e
> --- /dev/null
> +++ b/t/t2081-parallel-checkout-collisions.sh
> @@ -0,0 +1,162 @@
> +#!/bin/sh
> +
> +test_description="path collisions during parallel checkout
> +
> +Parallel checkout must detect path collisions to:
> +
> +1) Avoid racily writing to different paths that represent the same file on disk.
> +2) Report the colliding entries on clone.
> +
> +The tests in this file exercise parallel checkout's collision detection code in
> +both these mechanics.
> +"
> +
> +. ./test-lib.sh
> +. "$TEST_DIRECTORY/lib-parallel-checkout.sh"

> +
> +TEST_ROOT="$PWD"
> +
> +test_expect_success CASE_INSENSITIVE_FS 'setup' '
> +	empty_oid=$(git hash-object -w --stdin </dev/null) &&
> +	cat >objs <<-EOF &&
> +	100644 $empty_oid	FILE_X
> +	100644 $empty_oid	FILE_x
> +	100644 $empty_oid	file_X
> +	100644 $empty_oid	file_x
> +	EOF
> +	git update-index --index-info <objs &&
> +	git commit -m "colliding files" &&
> +	git tag basename_collision &&
> +
> +	write_script "$TEST_ROOT"/logger_script <<-\EOF
> +	echo "$@" >>filter.log
> +	EOF
> +'
> +
> +test_workers_in_event_trace ()
> +{
> +	test $1 -eq $(grep ".event.:.child_start..*checkout--worker" $2 | wc -l)
> +}
> +
> +test_expect_success CASE_INSENSITIVE_FS 'worker detects basename collision' '
> +	GIT_TRACE2_EVENT="$(pwd)/trace" git \
> +		-c checkout.workers=2 -c checkout.thresholdForParallelism=0 \
> +		checkout . &&
> +
> +	test_workers_in_event_trace 2 trace &&
> +	collisions=$(grep -i "category.:.pcheckout.,.key.:.collision/basename.,.value.:.file_x.}" trace | wc -l) &&
> +	test $collisions -eq 3
> +'
> +
> +test_expect_success CASE_INSENSITIVE_FS 'worker detects dirname collision' '
> +	test_config filter.logger.smudge "\"$TEST_ROOT/logger_script\" %f" &&
> +	empty_oid=$(git hash-object -w --stdin </dev/null) &&
> +
> +	# By setting a filter command to "a", we make it ineligible for parallel
> +	# checkout, and thus it is checked out *first*. This way we can ensure
> +	# that "A/B" and "A/C" will both collide with the regular file "a".
> +	#
> +	attr_oid=$(echo "a filter=logger" | git hash-object -w --stdin) &&
> +
> +	cat >objs <<-EOF &&
> +	100644 $empty_oid	A/B
> +	100644 $empty_oid	A/C
> +	100644 $empty_oid	a
> +	100644 $attr_oid	.gitattributes
> +	EOF
> +	git rm -rf . &&
> +	git update-index --index-info <objs &&
> +
> +	rm -f trace filter.log &&
> +	GIT_TRACE2_EVENT="$(pwd)/trace" git \
> +		-c checkout.workers=2 -c checkout.thresholdForParallelism=0 \
> +		checkout . &&
> +
> +	# Check that "a" (and only "a") was filtered
> +	echo a >expected.log &&
> +	test_cmp filter.log expected.log &&
> +
> +	# Check that it used the right number of workers and detected the collisions
> +	test_workers_in_event_trace 2 trace &&
> +	grep "category.:.pcheckout.,.key.:.collision/dirname.,.value.:.A/B.}" trace &&
> +	grep "category.:.pcheckout.,.key.:.collision/dirname.,.value.:.A/C.}" trace
> +'
> +
> +test_expect_success SYMLINKS,CASE_INSENSITIVE_FS 'do not follow symlinks colliding with leading dir' '
> +	empty_oid=$(git hash-object -w --stdin </dev/null) &&
> +	symlink_oid=$(echo "./e" | git hash-object -w --stdin) &&
> +	mkdir e &&
> +
> +	cat >objs <<-EOF &&
> +	120000 $symlink_oid	D
> +	100644 $empty_oid	d/x
> +	100644 $empty_oid	e/y
> +	EOF
> +	git rm -rf . &&
> +	git update-index --index-info <objs &&
> +
> +	set_checkout_config 2 0 &&
> +	test_checkout_workers 2 git checkout . &&
> +	test_path_is_dir e &&
> +	test_path_is_missing e/x
> +'
> +
> +# The two following tests check that parallel checkout correctly reports
> +# colliding entries on clone. The sequential code detects a collision by
> +# calling lstat() before trying to open(O_CREAT) a file. (Note that this only
> +# works for clone.) Then, to find the pair of a colliding item k, it searches
> +# cache_entry[0, k-1]. This is not sufficient in parallel checkout because:
> +#
> +# - A colliding file may be created between the lstat() and open() calls;
> +# - A colliding entry might appear in the second half of the cache_entry array.
> +#
> +test_expect_success CASE_INSENSITIVE_FS 'collision report on clone (w/ racy file creation)' '
> +	git reset --hard basename_collision &&
> +	set_checkout_config 2 0 &&
> +	test_checkout_workers 2 git clone . clone-repo 2>stderr &&
> +
> +	grep FILE_X stderr &&
> +	grep FILE_x stderr &&
> +	grep file_X stderr &&
> +	grep file_x stderr &&
> +	grep "the following paths have collided" stderr
> +'
> +
> +# This test ensures that the collision report code is correctly looking for
> +# colliding peers in the second half of the cache_entry array. This is done by
> +# defining a smudge command for the *last* array entry, which makes it
> +# non-eligible for parallel-checkout. Thus, it is checked out *first*, before
> +# spawning the workers.
> +#
> +# Note: this test doesn't work on Windows because, on this system, the
> +# collision report code uses strcmp() to find the colliding pairs when
> +# core.ignoreCase is false. And we need this setting for this test so that only
> +# 'file_x' matches the pattern of the filter attribute. But the test works on
> +# OSX, where the colliding pairs are found using inode.
> +#
> +test_expect_success CASE_INSENSITIVE_FS,!MINGW,!CYGWIN \
> +	'collision report on clone (w/ colliding peer after the detected entry)' '
> +
> +	test_config_global filter.logger.smudge "\"$TEST_ROOT/logger_script\" %f" &&
> +	git reset --hard basename_collision &&
> +	echo "file_x filter=logger" >.gitattributes &&
> +	git add .gitattributes &&
> +	git commit -m "filter for file_x" &&
> +
> +	rm -rf clone-repo &&
> +	set_checkout_config 2 0 &&
> +	test_checkout_workers 2 \
> +		git -c core.ignoreCase=false clone . clone-repo 2>stderr &&
> +
> +	grep FILE_X stderr &&
> +	grep FILE_x stderr &&
> +	grep file_X stderr &&
> +	grep file_x stderr &&
> +	grep "the following paths have collided" stderr &&
> +
> +	# Check that only "file_x" was filtered
> +	echo file_x >expected.log &&
> +	test_cmp clone-repo/filter.log expected.log
> +'
> +
> +test_done
> --
> 2.30.1
>