Replace deprecated_target_wait_hook by observers

Commit b60cea7 (Make target_wait options use enum flags) broke
deprecated_target_wait_hook usage: there's a commit comment telling
this hook has not been converted.

Rather than trying to mend it, this patch replaces the hook by two
target_wait observers:

target_pre_wait (ptid_t ptid)
target_post_wait (ptid_t event_ptid)

Upon target_wait entry, target_pre_wait is notified with the ptid
passed to target_wait. Upon exit, target_post_wait is notified with
the event ptid returned by target_wait. Should an exception occur,
event_ptid is null_ptid.

This change benefits to Insight (out-of-tree): there's no real use of the
late hook in gdb itself.

gdb/infrun.c

@@ -367,7 +367,7 @@ show_stop_on_solib_events (struct ui_file *file, int from_tty,
 static bool stop_print_frame;
 
 /* This is a cached copy of the target/ptid/waitstatus of the last
-   event returned by target_wait()/deprecated_target_wait_hook().
+   event returned by target_wait().
    This information is returned by get_last_target_status().  */
 static process_stratum_target *target_last_proc_target;
 static ptid_t target_last_wait_ptid;
@@ -3515,7 +3515,6 @@ static ptid_t
 do_target_wait_1 (inferior *inf, ptid_t ptid,
 		  target_waitstatus *status, target_wait_flags options)
 {
-  ptid_t event_ptid;
   struct thread_info *tp;
 
   /* We know that we are looking for an event in the target of inferior
@@ -3630,12 +3629,7 @@ do_target_wait_1 (inferior *inf, ptid_t ptid,
   if (!target_can_async_p ())
     options &= ~TARGET_WNOHANG;
 
-  if (deprecated_target_wait_hook)
-    event_ptid = deprecated_target_wait_hook (ptid, status, options);
-  else
-    event_ptid = target_wait (ptid, status, options);
-
-  return event_ptid;
+  return target_wait (ptid, status, options);
 }
 
 /* Wrapper for target_wait that first checks whether threads have
@@ -4591,10 +4585,7 @@ poll_one_curr_target (struct target_waitstatus *ws)
      don't get any event.  */
   target_dcache_invalidate ();
 
-  if (deprecated_target_wait_hook)
-    event_ptid = deprecated_target_wait_hook (minus_one_ptid, ws, TARGET_WNOHANG);
-  else
-    event_ptid = target_wait (minus_one_ptid, ws, TARGET_WNOHANG);
+  event_ptid = target_wait (minus_one_ptid, ws, TARGET_WNOHANG);
 
   if (debug_infrun)
     print_target_wait_results (minus_one_ptid, event_ptid, *ws);

gdb/infrun.h

@@ -124,9 +124,8 @@ extern process_stratum_target *user_visible_resume_target (ptid_t resume_ptid);
 extern int normal_stop (void);
 
 /* Return the cached copy of the last target/ptid/waitstatus returned
-   by target_wait()/deprecated_target_wait_hook().  The data is
-   actually cached by handle_inferior_event(), which gets called
-   immediately after target_wait()/deprecated_target_wait_hook().  */
+   by target_wait().  The data is actually cached by handle_inferior_event(),
+   which gets called immediately after target_wait().  */
 extern void get_last_target_status (process_stratum_target **target,
 				    ptid_t *ptid,
 				    struct target_waitstatus *status);

gdb/interps.c

@@ -357,7 +357,6 @@ clear_interpreter_hooks (void)
   deprecated_readline_hook = 0;
   deprecated_readline_end_hook = 0;
   deprecated_context_hook = 0;
-  deprecated_target_wait_hook = 0;
   deprecated_call_command_hook = 0;
   deprecated_error_begin_hook = 0;
 }

gdb/observable.c

@@ -79,6 +79,8 @@ DEFINE_OBSERVABLE (styling_changed);
 DEFINE_OBSERVABLE (current_source_symtab_and_line_changed);
 DEFINE_OBSERVABLE (gdb_exiting);
 DEFINE_OBSERVABLE (connection_removed);
+DEFINE_OBSERVABLE (target_pre_wait);
+DEFINE_OBSERVABLE (target_post_wait);
 
 } /* namespace observers */
 } /* namespace gdb */

gdb/observable.h

@@ -256,6 +256,12 @@ extern observable<int> gdb_exiting;
 /* When a connection is removed.  */
 extern observable<process_stratum_target */* target */> connection_removed;
 
+/* About to enter target_wait (). */
+extern observable <ptid_t /* ptid */> target_pre_wait;
+
+/* About to leave target_wait (). */
+extern observable <ptid_t /* event_ptid */> target_post_wait;
+
 } /* namespace observers */
 
 } /* namespace gdb */

gdb/target.c

@@ -26,6 +26,7 @@
 #include "symtab.h"
 #include "inferior.h"
 #include "infrun.h"
+#include "observable.h"
 #include "bfd.h"
 #include "symfile.h"
 #include "objfiles.h"
@@ -2609,7 +2610,18 @@ target_wait (ptid_t ptid, struct target_waitstatus *status,
   if (!target_can_async_p (target))
     gdb_assert ((options & TARGET_WNOHANG) == 0);
 
-  return target->wait (ptid, status, options);
+  try
+    {
+      gdb::observers::target_pre_wait.notify (ptid);
+      ptid_t event_ptid = target->wait (ptid, status, options);
+      gdb::observers::target_post_wait.notify (event_ptid);
+      return event_ptid;
+    }
+  catch (...)
+    {
+      gdb::observers::target_post_wait.notify (null_ptid);
+      throw;
+    }
 }
 
 /* See target.h.  */

gdb/top.c

@@ -247,13 +247,6 @@ void (*deprecated_readline_end_hook) (void);
 void (*deprecated_attach_hook) (void);
 void (*deprecated_detach_hook) (void);
 
-/* Called when going to wait for the target.  Usually allows the GUI
-   to run while waiting for target events.  */
-
-ptid_t (*deprecated_target_wait_hook) (ptid_t ptid,
-				       struct target_waitstatus *status,
-				       int options);
-
 /* Used by UI as a wrapper around command execution.  May do various
    things like enabling/disabling buttons, etc...  */