gdb: add threads debugging switch

Add new commands:

  set debug threads on|off
  show debug threads

Prints additional debug information relating to thread creation and
deletion.

GDB already announces when threads are created of course.... most of
the time, but sometimes threads are added silently, in which case this
debug message is the only mechanism to see the thread being added.
Also, though GDB does announce when a thread exits, it doesn't
announce when the thread object is deleted, I've added a debug message
for that.

Additionally, having message printed through the debug system will
cause the messages to be nested to an appropriate depth when other
debug sub-systems are turned on (especially things like `infrun` and
`lin-lwp`).

diff --git a/gdb/NEWS b/gdb/NEWS
index 935a10c91ebe6feab628f78138961b10f7331e80..1e4afa91bc5931446e7d4bc45c45b485b0884749 100644 (file)
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -60,6 +60,10 @@ exit
   You can now exit GDB by using the new command "exit", in addition to
   the existing "quit" command.
 
+set debug threads on|off
+show debug threads
+  Print additional debug messages about thread creation and deletion.
+
 * Changed commands
 
 maint packet

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 0c517b464d84e7f41d185230df5721ea82fbcca6..2d3414175c1a3183a55544e8078cb88a115c42c2 100644 (file)
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -3899,6 +3899,14 @@ Display current libthread_db search path.
 @itemx show debug libthread-db
 Turns on or off display of @code{libthread_db}-related events.
 Use @code{1} to enable, @code{0} to disable.
+
+@kindex set debug threads
+@kindex show debug threads
+@cindex debugging @code{threads}
+@item set debug threads @r{[}on@r{|}off@r{]}
+@itemx show debug threads
+When @samp{on} @value{GDBN} will print additional messages when
+threads are created and deleted.
 @end table
 
 @node Forks

diff --git a/gdb/gdbthread.h b/gdb/gdbthread.h
index e229a5f09bd4f5f0f122562ba8162fcd8b273448..66c525b42a7d07693659a541ab968df1a5fcf44f 100644 (file)
--- a/gdb/gdbthread.h
+++ b/gdb/gdbthread.h
@@ -38,6 +38,16 @@ struct symtab;
 struct inferior;
 struct process_stratum_target;
 
+/* When true, print debug messages related to GDB thread creation and
+   deletion.  */
+
+extern bool debug_threads;
+
+/* Print a "threads" debug statement.  */
+
+#define threads_debug_printf(fmt, ...) \
+  debug_prefixed_printf_cond (debug_threads, "threads", fmt, ##__VA_ARGS__)
+
 /* Frontend view of the thread state.  Possible extensions: stepping,
    finishing, until(ling),...
 
@@ -235,6 +245,7 @@ class thread_info : public refcounted_object,
 {
 public:
   explicit thread_info (inferior *inf, ptid_t ptid);
+  ~thread_info ();
 
   bool deletable () const;
 

diff --git a/gdb/inferior.c b/gdb/inferior.c
index 40ab3e7e90b9e5d8979fcf634fa6af197ea7e6d4..72b7c6181ad14fdbb2a35b4026cb4b84164a454f 100644 (file)
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -179,6 +179,8 @@ inferior::clear_thread_list (bool silent)
 {
   thread_list.clear_and_dispose ([=] (thread_info *thr)
     {
+      threads_debug_printf ("deleting thread %s, silent = %d",
+                           thr->ptid.to_string ().c_str (), silent);
       set_thread_exited (thr, silent);
       if (thr->deletable ())
        delete thr;

diff --git a/gdb/thread.c b/gdb/thread.c
index 6c792eccb8f69e450c12035a9a49e9b4db481718..ebaed1c6ca429ea878ece84a79d369bdfa27b590 100644 (file)
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -49,6 +49,19 @@
 #include "inline-frame.h"
 #include "stack.h"
 
+/* See gdbthread.h.  */
+
+bool debug_threads = false;
+
+/* Implement 'show debug threads'.  */
+
+static void
+show_debug_threads (struct ui_file *file, int from_tty,
+                   struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Thread debugging is \"%s\".\n"), value);
+}
+
 /* Definition of struct thread_info exported to gdbthread.h.  */
 
 /* Prototypes for local functions.  */
@@ -234,6 +247,9 @@ new_thread (struct inferior *inf, ptid_t ptid)
 {
   thread_info *tp = new thread_info (inf, ptid);
 
+  threads_debug_printf ("creating a new thread object, inferior %d, ptid %s",
+                       inf->num, ptid.to_string ().c_str ());
+
   inf->thread_list.push_back (*tp);
 
   /* A thread with this ptid should not exist in the map yet.  */
@@ -251,6 +267,10 @@ add_thread_silent (process_stratum_target *targ, ptid_t ptid)
 
   inferior *inf = find_inferior_ptid (targ, ptid);
 
+  threads_debug_printf ("add thread to inferior %d, ptid %s, target %s",
+                       inf->num, ptid.to_string ().c_str (),
+                       targ->shortname ());
+
   /* We may have an old thread with the same id in the thread list.
      If we do, it must be dead, otherwise we wouldn't be adding a new
      thread with the same id.  The OS is reusing this id --- delete
@@ -302,6 +322,13 @@ thread_info::thread_info (struct inferior *inf_, ptid_t ptid_)
 
 /* See gdbthread.h.  */
 
+thread_info::~thread_info ()
+{
+  threads_debug_printf ("thread %s", this->ptid.to_string ().c_str ());
+}
+
+/* See gdbthread.h.  */
+
 bool
 thread_info::deletable () const
 {
@@ -434,6 +461,9 @@ delete_thread_1 (thread_info *thr, bool silent)
 {
   gdb_assert (thr != nullptr);
 
+  threads_debug_printf ("deleting thread %s, silent = %d",
+                       thr->ptid.to_string ().c_str (), silent);
+
   set_thread_exited (thr, silent);
 
   if (!thr->deletable ())
@@ -2192,6 +2222,14 @@ Show printing of thread events (such as thread start and exit)."), NULL,
                           show_print_thread_events,
                           &setprintlist, &showprintlist);
 
+  add_setshow_boolean_cmd ("threads", class_maintenance, &debug_threads, _("\
+Set thread debugging."), _("\
+Show thread debugging."), _("\
+When on messages about thread creation and deletion are printed."),
+                          nullptr,
+                          show_debug_threads,
+                          &setdebuglist, &showdebuglist);
+
   create_internalvar_type_lazy ("_thread", &thread_funcs, NULL);
   create_internalvar_type_lazy ("_gthread", &gthread_funcs, NULL);
 }