checkout.c: enable fscache for checkout again

This is retry of git-for-windows#1419.

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

@@ -360,6 +360,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 	state.istate = &the_index;
 
 	enable_delayed_checkout(&state);
+	enable_fscache(1);
 	for (pos = 0; pos < active_nr; pos++) {
 		struct cache_entry *ce = active_cache[pos];
 		if (ce->ce_flags & CE_MATCHED) {
@@ -374,6 +375,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 			pos = skip_same_name(ce, pos) - 1;
 		}
 	}
+	enable_fscache(0);
 	errs |= finish_delayed_checkout(&state);
 
 	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))

compat/win32/fscache.c

@@ -411,6 +411,18 @@ 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

@@ -367,6 +367,9 @@ static int write_entry(struct cache_entry *ce,
 	}
 
 finish:
+	/* Flush cached lstat in fscache after writing to disk. */
+	flush_fscache();
+
 	if (state->refresh_cache) {
 		assert(state->istate);
 		if (!fstat_done)

git-compat-util.h

@@ -1290,6 +1290,10 @@ static inline int is_missing_file_error(int errno_)
 #define is_fscache_enabled(path) (0)
 #endif
 
+#ifndef flush_fscache
+#define flush_fscache() /* noop */
+#endif
+
 extern int cmd_main(int, const char **);
 
 /*

t/t7201-co.sh

@@ -32,6 +32,42 @@ 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 &&