[gdb/cli] Use captured per_command_time in worker threads

With test-case gdb.base/maint.exp, I ran into:
...
(gdb) file maint^M
Reading symbols from maint...^M
(gdb) mt set per-command on^M
(gdb) Time for "DWARF indexing worker": ...^M
Time for "DWARF indexing worker": ...^M
Time for "DWARF indexing worker": ...^M
Time for "DWARF indexing worker": ...^M
Time for "DWARF skeletonless type units": ...^M
Time for "DWARF add parent map": ...^M
Time for "DWARF finalize worker": ...^M
Time for "DWARF finalize worker": ...^M
Time for "DWARF finalize worker": ...^M
Time for "DWARF finalize worker": ...^M
Time for "DWARF finalize worker": ...^M
FAIL: $exp: warnings: per-command: mt set per-command on (timeout)
mt set per-command off^M
2025-05-31 09:33:44.711 - command started^M
(gdb) PASS: $exp: warnings: per-command: mt set per-command off
...

I didn't manage to reproduce this by rerunning the test-case, but it's fairly
easy to reproduce using a file with more debug info, for instance gdb:
...
$ gdb -q -batch -ex "file build/gdb/gdb" -ex "mt set per-command on"
...

Due to the default "mt dwarf synchronous" == off, the file command starts
building the cooked index in the background, and returns immediately without
waiting for the result.

The subsequent "mt set per-command on" implies "mt set per-command time on",
which switches on displaying of per-command execution time.

The "Time for" lines are the result of those two commands, but these lines
shouldn't be there because "mt per-command time" == off at the point of
issuing the file command.

Fix this by capturing the per_command_time variable, and using the captured
value instead.

Tested on x86_64-linux.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

PR cli/33039
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33039

gdb/dwarf2/cooked-index-worker.c

@@ -246,7 +246,7 @@ void
 cooked_index_worker::done_reading ()
 {
   {
-    scoped_time_it time_it ("DWARF add parent map");
+    scoped_time_it time_it ("DWARF add parent map", m_per_command_time);
 
     for (auto &one_result : m_results)
       m_all_parents_map.add_map (*one_result.get_parent_map ());

gdb/dwarf2/cooked-index-worker.h

@@ -25,6 +25,8 @@
 #include "dwarf2/cooked-index-shard.h"
 #include "dwarf2/types.h"
 #include "dwarf2/read.h"
+#include "maint.h"
+#include "run-on-main-thread.h"
 
 #if CXX_STD_THREAD
 #include <mutex>
@@ -216,8 +218,12 @@ public:
 
   explicit cooked_index_worker (dwarf2_per_objfile *per_objfile)
     : m_per_objfile (per_objfile),
-      m_cache_store (global_index_cache, per_objfile->per_bfd)
-  { }
+      m_cache_store (global_index_cache, per_objfile->per_bfd),
+      m_per_command_time (per_command_time)
+  {
+    /* Make sure we capture per_command_time from the main thread.  */
+    gdb_assert (is_main_thread ());
+  }
   virtual ~cooked_index_worker ()
   { }
   DISABLE_COPY_AND_ASSIGN (cooked_index_worker);
@@ -307,6 +313,9 @@ protected:
   std::optional<gdb_exception> m_failed;
   /* An object used to write to the index cache.  */
   index_cache_store_context m_cache_store;
+
+  /* Captured value of per_command_time.  */
+  bool m_per_command_time;
 };
 
 using cooked_index_worker_up = std::unique_ptr<cooked_index_worker>;

gdb/dwarf2/cooked-index.c

@@ -104,7 +104,8 @@ cooked_index::set_contents ()
       const parent_map_map *parent_maps = m_state->get_parent_map_map ();
       finalizers.add_task ([=] ()
 	{
-	  scoped_time_it time_it ("DWARF finalize worker");
+	  scoped_time_it time_it ("DWARF finalize worker",
+				  m_state->m_per_command_time);
 	  this_shard->finalize (parent_maps);
 	});
     }

gdb/dwarf2/read.c

@@ -3464,7 +3464,7 @@ void
 cooked_index_worker_debug_info::process_skeletonless_type_units
   (dwarf2_per_objfile *per_objfile, cooked_index_worker_result *storage)
 {
-  scoped_time_it time_it ("DWARF skeletonless type units");
+  scoped_time_it time_it ("DWARF skeletonless type units", m_per_command_time);
 
   /* Skeletonless TUs in DWP files without .gdb_index is not supported yet.  */
   if (per_objfile->per_bfd->dwp_file == nullptr)
@@ -3573,7 +3573,7 @@ cooked_index_worker_debug_info::do_reading ()
       gdb_assert (iter != last);
       workers.add_task ([this, task_count, iter, last] ()
 	{
-	  scoped_time_it time_it ("DWARF indexing worker");
+	  scoped_time_it time_it ("DWARF indexing worker", m_per_command_time);
 	  process_units (task_count, iter, last);
 	});
 

gdb/maint.c

@@ -920,9 +920,9 @@ maintenance_show_worker_threads (struct ui_file *file, int from_tty,
 }
 
 
-/* If true, display time usage both at startup and for each command.  */
+/* See maint.h.  */
 
-static bool per_command_time;
+bool per_command_time;
 
 /* If true, display space usage both at startup and for each command.  */
 
@@ -1175,8 +1175,8 @@ per-thread run time information not available on this platform"));
 
 /* See maint.h.  */
 
-scoped_time_it::scoped_time_it (const char *what)
-  : m_enabled (per_command_time),
+scoped_time_it::scoped_time_it (const char *what, bool enabled)
+  : m_enabled (enabled),
     m_what (what),
     m_start_wall (m_enabled
 		  ? std::chrono::steady_clock::now ()

gdb/maint.h

@@ -70,13 +70,17 @@ class scoped_command_stats
   int m_start_nr_blocks;
 };
 
+/* If true, display time usage both at startup and for each command.  */
+
+extern bool per_command_time;
+
 /* RAII structure used to measure the time spent by the current thread in a
    given scope.  */
 
 struct scoped_time_it
 {
   /* WHAT is the prefix to show when the summary line is printed.  */
-  scoped_time_it (const char *what);
+  scoped_time_it (const char *what, bool enabled = per_command_time);
 
   DISABLE_COPY_AND_ASSIGN (scoped_time_it);
   ~scoped_time_it ();