[PATCH v2] Ensure index cache entry written in test

[Tom Tromey <tromey@adacore.com>]

Now that index cache files are written in the background, one test in
index-cache.exp is racy -- it assumes that the cache file will have
been written during startup.

This patch fixes the problem by introducing a new maintenance command
to wait for all pending writes to the index cache.
---
 gdb/NEWS                               |  3 +++
 gdb/doc/gdb.texinfo                    |  6 ++++++
 gdb/dwarf2/cooked-index.c              | 15 +++++++++++++++
 gdb/testsuite/gdb.base/index-cache.exp |  2 ++
 4 files changed, 26 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index c32ff92c98a..8827efaefb6 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -68,6 +68,9 @@ maintenance info frame-unwinders
   List the frame unwinders currently in effect, starting with the highest
   priority.
 
+maintenance wait-for-index-cache
+  Wait until all pending writes to the index cache have completed.
+
 set always-read-ctf on|off
 show always-read-ctf
   When off, CTF is only read if DWARF is not present.  When on, CTF is
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index bfda7edc4f7..954f1481dae 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -41374,6 +41374,12 @@ give an error.
 For platforms that do support creating the backtrace this feature is
 @code{on} by default.
 
+@kindex maint wait-for-index-cache
+@item maint wait-for-index-cache
+Wait until all pending writes to the index cache have completed.  This
+is used by the test suite to avoid races when the index cache is being
+updated by a worker thread.
+
 @kindex maint with
 @item maint with @var{setting} [@var{value}] [-- @var{command}]
 Like the @code{with} command, but works with @code{maintenance set}
diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 47746aa9905..d09faed268d 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -33,6 +33,7 @@
 #include "gdbsupport/selftest.h"
 #include <chrono>
 #include <unordered_set>
+#include "cli/cli-cmds.h"
 
 /* We don't want gdb to exit while it is in the process of writing to
    the index cache.  So, all live cooked index vectors are stored
@@ -640,6 +641,14 @@ wait_for_index_cache (int)
     item->wait_completely ();
 }
 
+/* A maint command to wait for the cache.  */
+
+static void
+maintenance_wait_for_index_cache (const char *args, int from_tty)
+{
+  wait_for_index_cache (0);
+}
+
 void _initialize_cooked_index ();
 void
 _initialize_cooked_index ()
@@ -648,5 +657,11 @@ _initialize_cooked_index ()
   selftests::register_test ("cooked_index_entry::compare", test_compare);
 #endif
 
+  add_cmd ("wait-for-index-cache", class_maintenance,
+	   maintenance_wait_for_index_cache, _("\
+Usage: maintenance wait-for-index-cache\n\
+Wait until all pending writes to the index cache have completed."),
+	   &maintenancelist);
+
   gdb::observers::gdb_exiting.attach (wait_for_index_cache, "cooked-index");
 }
diff --git a/gdb/testsuite/gdb.base/index-cache.exp b/gdb/testsuite/gdb.base/index-cache.exp
index 0614d4ee2db..7fdf90c2c24 100644
--- a/gdb/testsuite/gdb.base/index-cache.exp
+++ b/gdb/testsuite/gdb.base/index-cache.exp
@@ -159,6 +159,8 @@ proc_with_prefix test_cache_enabled_miss { cache_dir } {
 
     run_test_with_flags $cache_dir on {
 
+	gdb_test_no_output "maintenance wait-for-index-cache"
+
 	lassign [ls_host $cache_dir] ret files_after
 	set nfiles_created [expr [llength $files_after] - [llength $files_before]]
 	if { $expecting_index_cache_use } {
-- 
2.39.1