checkout.c: enable fscache for checkout again

This is retry of #1419.

I added flush_fscache macro to flush cached stats after disk writing
with tests for regression reported in #1438 and #1442.

git checkout checks each file path in sorted order, so cache flushing does not
make performance worse unless we have large number of modified files in
a directory containing many files.

Using chromium repository, I tested `git checkout .` performance when I
delete 10 files in different directories.
With this patch:
TotalSeconds: 4.307272
TotalSeconds: 4.4863595
TotalSeconds: 4.2975562
Avg: 4.36372923333333

Without this patch:
TotalSeconds: 20.9705431
TotalSeconds: 22.4867685
TotalSeconds: 18.8968292
Avg: 20.7847136

I confirmed this patch passed all tests in t/ with core_fscache=1.

Signed-off-by: Takuto Ikuta <tikuta@chromium.org>

builtin/checkout.c

@@ -391,6 +391,7 @@ static int checkout_worktree(const struct checkout_opts *opts,
 	if (pc_workers > 1)
 		init_parallel_checkout();
 
+	enable_fscache(1);
 	for (pos = 0; pos < active_nr; pos++) {
 		struct cache_entry *ce = active_cache[pos];
 		if (ce->ce_flags & CE_MATCHED) {
@@ -415,6 +416,7 @@ static int checkout_worktree(const struct checkout_opts *opts,
 		errs |= run_parallel_checkout(&state, pc_workers, pc_threshold,
 					      NULL, NULL);
 	mem_pool_discard(&ce_mem_pool, should_validate_cache_entries());
+	enable_fscache(0);
 	remove_marked_cache_entries(&the_index, 1);
 	remove_scheduled_dirs();
 	errs |= finish_delayed_checkout(&state, &nr_checkouts, opts->show_progress);

compat/win32/fscache.c

@@ -426,6 +426,18 @@ int fscache_enable(int enable)
 	return result;
 }
 
+/*
+ * Flush cached stats result when fscache is enabled.
+ */
+void fscache_flush(void)
+{
+	if (enabled) {
+		EnterCriticalSection(&mutex);
+		fscache_clear();
+		LeaveCriticalSection(&mutex);
+	}
+}
+
 /*
  * Lstat replacement, uses the cache if enabled, otherwise redirects to
  * mingw_lstat.

compat/win32/fscache.h

@@ -7,6 +7,9 @@ int fscache_enable(int enable);
 int fscache_enabled(const char *path);
 #define is_fscache_enabled(path) fscache_enabled(path)
 
+void fscache_flush(void);
+#define flush_fscache() fscache_flush()
+
 DIR *fscache_opendir(const char *dir);
 int fscache_lstat(const char *file_name, struct stat *buf);
 

entry.c

@@ -386,6 +386,9 @@ static int write_entry(struct cache_entry *ce, char *path, struct conv_attrs *ca
 	}
 
 finish:
+	/* Flush cached lstat in fscache after writing to disk. */
+	flush_fscache();
+
 	if (state->refresh_cache) {
 		if (!fstat_done && lstat(ce->name, &st) < 0)
 			return error_errno("unable to stat just-written file %s",

git-compat-util.h

@@ -1497,6 +1497,10 @@ static inline int is_missing_file_error(int errno_)
 #define is_fscache_enabled(path) (0)
 #endif
 
+#ifndef flush_fscache
+#define flush_fscache() /* noop */
+#endif
+
 int cmd_main(int, const char **);
 
 /*

parallel-checkout.c

@@ -633,6 +633,7 @@ static void write_items_sequentially(struct checkout *state)
 {
 	size_t i;
 
+	flush_fscache();
 	for (i = 0; i < parallel_checkout.nr; i++) {
 		struct parallel_checkout_item *pc_item = &parallel_checkout.items[i];
 		write_pc_item(pc_item, state);

t/t7201-co.sh

@@ -35,6 +35,42 @@ fill () {
 }
 
 
+test_expect_success MINGW 'fscache flush cache' '
+
+	git init fscache-test &&
+	cd fscache-test &&
+	git config core.fscache 1 &&
+	echo A > test.txt &&
+	git add test.txt &&
+	git commit -m A &&
+	echo B >> test.txt &&
+	git checkout . &&
+	test -z "$(git status -s)" &&
+	echo A > expect.txt &&
+	test_cmp expect.txt test.txt &&
+	cd .. &&
+	rm -rf fscache-test
+'
+
+test_expect_success MINGW 'fscache flush cache dir' '
+
+	git init fscache-test &&
+	cd fscache-test &&
+	git config core.fscache 1 &&
+	echo A > test.txt &&
+	git add test.txt &&
+	git commit -m A &&
+	rm test.txt &&
+	mkdir test.txt &&
+	touch test.txt/test.txt &&
+	git checkout . &&
+	test -z "$(git status -s)" &&
+	echo A > expect.txt &&
+	test_cmp expect.txt test.txt &&
+	cd .. &&
+	rm -rf fscache-test
+'
+
 test_expect_success setup '
 	fill x y z >same &&
 	fill 1 2 3 4 5 6 7 8 >one &&