[PATCH] Let user C-c when waiting for DWARF index finalization

[Tom Tromey <tromey@adacore.com>]

In PR gdb/29854, Simon pointed out that it would be good to be able to
use C-c when the DWARF cooked index is waiting for finalization.  The
idea here is to be able to interrupt a command like "break" -- not to
stop the finalization process itself, which runs in a worker thread.

This patch implements this idea, by changing the index wait functions
to, by default, allow a quit.  Polling is done, because there doesn't
seem to be a better way to interrupt a wait on a std::future.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29854
---
 gdb/dwarf2/cooked-index.c | 17 +++++++++++++++++
 gdb/dwarf2/cooked-index.h | 11 +++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 0aa026c7779..a0b75a311b1 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -25,6 +25,7 @@
 #include "ada-lang.h"
 #include "split-name.h"
 #include <algorithm>
+#include <chrono>
 
 /* Hash function for cooked_index_entry.  */
 
@@ -282,6 +283,22 @@ cooked_index::find (gdb::string_view name, bool completing)
   return range (lower, upper);
 }
 
+/* See cooked-index.h.  */
+
+void
+cooked_index::wait (bool allow_quit)
+{
+  if (allow_quit)
+    {
+      using namespace std::chrono_literals;
+      auto duration = 15ms;
+      while (m_future.wait_for (duration) == std::future_status::timeout)
+	QUIT;
+    }
+  else
+    m_future.wait ();
+}
+
 cooked_index_vector::cooked_index_vector (vec_type &&vec)
   : m_vector (std::move (vec))
 {
diff --git a/gdb/dwarf2/cooked-index.h b/gdb/dwarf2/cooked-index.h
index 2ea32781be5..5412149588a 100644
--- a/gdb/dwarf2/cooked-index.h
+++ b/gdb/dwarf2/cooked-index.h
@@ -212,10 +212,7 @@ class cooked_index
   void finalize ();
 
   /* Wait for this index's finalization to be complete.  */
-  void wait ()
-  {
-    m_future.wait ();
-  }
+  void wait (bool allow_quit = true);
 
   friend class cooked_index_vector;
 
@@ -325,8 +322,10 @@ class cooked_index_vector : public dwarf_scanner_base
        end up writing to freed memory.  Waiting for finalization to
        complete avoids this problem; and the cost seems ignorable
        because creating and immediately destroying the debug info is a
-       relatively rare thing to do.  */
-    wait ();
+       relatively rare thing to do.  Do not allow quitting from this
+       wait.  */
+    for (auto &item : m_vector)
+      item->wait (false);
   }
 
   /* A range over a vector of subranges.  */
-- 
2.34.3