Add $_gthread convenience variable

This commit adds a new $_gthread convenience variable, that is like
$_thread, but holds the current thread's global thread id.

gdb/ChangeLog:
2016-01-13  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention $_gthread.
	* gdbthread.h (struct thread_info) <global_num>: Mention
	$_gthread.
	* thread.c (thread_num_make_value_helper): New function.
	(thread_id_make_value): Delete.
	(thread_id_per_inf_num_make_value, global_thread_id_make_value):
	New.
	(thread_funcs): Adjust.
	(gthread_funcs): New.
	(_initialize_thread): Register $_gthread variable.

gdb/testsuite/ChangeLog:
2016-01-13  Pedro Alves  <palves@redhat.com>

	* gdb.base/default.exp: Expect $_gthread as well.
	* gdb.multi/tids.exp: Test $_gthread.
	* gdb.threads/thread-specific.exp: Test $_gthread.

gdb/doc/ChangeLog:
2016-01-13  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Threads): Document the $_gthread convenience
	variable.
	(Convenience Vars): Likewise.

10 files changed, 89 insertions, 11 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 603af22cd39..e0719641e89 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,18 @@
 2016-01-13  Pedro Alves  <palves@redhat.com>
 
+	* NEWS: Mention $_gthread.
+	* gdbthread.h (struct thread_info) <global_num>: Mention
+	$_gthread.
+	* thread.c (thread_num_make_value_helper): New function.
+	(thread_id_make_value): Delete.
+	(thread_id_per_inf_num_make_value, global_thread_id_make_value):
+	New.
+	(thread_funcs): Adjust.
+	(gthread_funcs): New.
+	(_initialize_thread): Register $_gthread variable.
+
+2016-01-13  Pedro Alves  <palves@redhat.com>
+
 	* NEWS: Mention "info threads -gid".
 	* gdbthread.h (struct thread_info) <global_num>: Mention "info
 	threads -gid".
diff --git a/gdb/NEWS b/gdb/NEWS
index 024c184879e..d9cbb800646 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -22,7 +22,7 @@
 
   GDB now maintains a second thread ID per thread, referred to as the
   global thread ID, which is the new equivalent of thread numbers in
-  previous releases.
+  previous releases.  See also $_gthread below.
 
   For backwards compatibility, MI's thread IDs always refer to global
   IDs.
@@ -37,6 +37,9 @@
 * You can use "info threads -gid" to display the global thread ID of
   all threads.
 
+* The new convenience variable $_gthread holds the global number of
+  the current thread.
+
 * The new convenience variable $_inferior holds the number of the
   current inferior.
 
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index d723276a9af..4b59057eeb8 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,11 @@
 2016-01-13  Pedro Alves  <palves@redhat.com>
 
+	* gdb.texinfo (Threads): Document the $_gthread convenience
+	variable.
+	(Convenience Vars): Likewise.
+
+2016-01-13  Pedro Alves  <palves@redhat.com>
+
 	* gdb.texinfo (Threads): Document "info threads -gid".
 
 2016-01-13  Pedro Alves  <palves@redhat.com>
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 654efa425fe..7da31c84c53 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -2937,8 +2937,10 @@ thread.  In other words, @value{GDBN} assigns a thread number to the
 program's ``main thread'' even if the program is not multi-threaded.
 
 @vindex $_thread@r{, convenience variable}
-The debugger convenience variable @samp{$_thread} contains the
-per-inferior thread number of the current thread.  You may find this
+@vindex $_gthread@r{, convenience variable}
+The debugger convenience variables @samp{$_thread} and
+@samp{$_gthread} contain, respectively, the per-inferior thread number
+and the global thread number of the current thread.  You may find this
 useful in writing breakpoint conditional expressions, command scripts,
 and so forth.  @xref{Convenience Vars,, Convenience Variables}, for
 general information on convenience variables.
@@ -10459,6 +10461,9 @@ Programs, ,Debugging Multiple Inferiors and Programs}.
 @item $_thread
 The thread number of the current thread.  @xref{thread numbers}.
 
+@item $_gthread
+The global number of the current thread.  @xref{global thread numbers}.
+
 @end table
 
 @node Convenience Funs
diff --git a/gdb/gdbthread.h b/gdb/gdbthread.h
index bfc91245a43..37c2837b205 100644
--- a/gdb/gdbthread.h
+++ b/gdb/gdbthread.h
@@ -217,7 +217,8 @@ struct thread_info
      thread has its own unique global ID.  */
 
   /* The thread's global GDB thread number.  This is exposed to MI,
-     Python/Scheme and visible with "info threads -gid".  */
+     Python/Scheme, visible with "info threads -gid", and is also what
+     the $_gthread convenience variable is bound to.  */
   int global_num;
 
   /* The per-inferior thread number.  This is unique in the inferior
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index c86351863c6..dcdc09cc1dc 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2016-01-13  Pedro Alves  <palves@redhat.com>
 
+	* gdb.base/default.exp: Expect $_gthread as well.
+	* gdb.multi/tids.exp: Test $_gthread.
+	* gdb.threads/thread-specific.exp: Test $_gthread.
+
+2016-01-13  Pedro Alves  <palves@redhat.com>
+
 	* gdb.multi/tids.exp: Test "info threads -gid".
 
 2016-01-13  Pedro Alves  <palves@redhat.com>
diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
index fec2cded525..10739cab636 100644
--- a/gdb/testsuite/gdb.base/default.exp
+++ b/gdb/testsuite/gdb.base/default.exp
@@ -587,6 +587,7 @@ set show_conv_list \
 	{$_sdata = void} \
 	{$_siginfo = void} \
 	{$_thread = 0} \
+	{$_gthread = 0} \
 	{$_inferior = 1} \
 	{$_exception = <error: No frame selected>} \
 	{$_probe_argc = <error: No frame selected>} \
diff --git a/gdb/testsuite/gdb.multi/tids.exp b/gdb/testsuite/gdb.multi/tids.exp
index b0c768fbc39..b72695d43dc 100644
--- a/gdb/testsuite/gdb.multi/tids.exp
+++ b/gdb/testsuite/gdb.multi/tids.exp
@@ -158,8 +158,9 @@ with_test_prefix "two inferiors" {
 	     "  2\.1 +2 +.*" \
 	     "  2\.2 +3 +.* thread_function1 .* at .*$srcfile:.*"]
 
-    # Confirm the convenience variable show the expected number.
+    # Confirm the convenience variables show the expected numbers.
     gdb_test "p \$_thread == 2" " = 1"
+    gdb_test "p \$_gthread == 4" " = 1"
 
     # Without an explicit inferior component, GDB defaults to the
     # current inferior.  Make sure we don't refer to a thread by
diff --git a/gdb/testsuite/gdb.threads/thread-specific.exp b/gdb/testsuite/gdb.threads/thread-specific.exp
index 2b75b6040e8..8f61f8867e8 100644
--- a/gdb/testsuite/gdb.threads/thread-specific.exp
+++ b/gdb/testsuite/gdb.threads/thread-specific.exp
@@ -66,7 +66,10 @@ clean_restart ${binfile}
 gdb_test_no_output "set print sevenbit-strings"
 gdb_test_no_output "set width 0"
 
+# As this test only runs a single inferior, $_thread and $_gthread
+# should match throughout.
 gdb_test {print $_thread} ".* = 0" "thread var when not running"
+gdb_test {print $_gthread} ".* = 0" "gthread var when not running"
 
 runto_main
 
@@ -82,6 +85,7 @@ if {[llength $threads] == 0} {
 }
 
 gdb_test {print $_thread} ".* = [lindex $threads 0]" "thread var in main"
+gdb_test {print $_gthread} ".* = [lindex $threads 0]" "gthread var in main"
 
 gdb_test_multiple "break $line thread [lindex $threads 0]" \
   "breakpoint $line main thread" {
@@ -120,6 +124,7 @@ if { $this_breakpoint != -1 } {
 
 if { $this_thread != -1 } {
     gdb_test {print $_thread} ".* = $this_thread" "thread var at break"
+    gdb_test {print $_gthread} ".* = $this_thread" "gthread var at break"
 } else {
     untested "thread var at break"
 }
diff --git a/gdb/thread.c b/gdb/thread.c
index 8ec6a38e391..cdd2a2f2655 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -2083,18 +2083,45 @@ update_thread_list (void)
   update_threads_executing ();
 }
 
+/* Return a new value for the selected thread's id.  Return a value of
+   0 if no thread is selected.  If GLOBAL is true, return the thread's
+   global number.  Otherwise return the per-inferior number.  */
+
+static struct value *
+thread_num_make_value_helper (struct gdbarch *gdbarch, int global)
+{
+  struct thread_info *tp = find_thread_ptid (inferior_ptid);
+  int int_val;
+
+  if (tp == NULL)
+    int_val = 0;
+  else if (global)
+    int_val = tp->global_num;
+  else
+    int_val = tp->per_inf_num;
+
+  return value_from_longest (builtin_type (gdbarch)->builtin_int, int_val);
+}
+
 /* Return a new value for the selected thread's per-inferior thread
    number.  Return a value of 0 if no thread is selected, or no
    threads exist.  */
 
 static struct value *
-thread_id_make_value (struct gdbarch *gdbarch, struct internalvar *var,
-		      void *ignore)
+thread_id_per_inf_num_make_value (struct gdbarch *gdbarch, struct internalvar *var,
+				  void *ignore)
 {
-  struct thread_info *tp = find_thread_ptid (inferior_ptid);
+  return thread_num_make_value_helper (gdbarch, 0);
+}
+
+/* Return a new value for the selected thread's global id.  Return a
+   value of 0 if no thread is selected, or no threads exist.  */
 
-  return value_from_longest (builtin_type (gdbarch)->builtin_int,
-			     (tp ? tp->per_inf_num : 0));
+static struct value *
+global_thread_id_make_value (struct gdbarch *gdbarch, struct internalvar *var,
+			     void *ignore)
+{
+  return thread_num_make_value_helper (gdbarch, 1);
 }
 
 /* Commands with a prefix of `thread'.  */
@@ -2104,7 +2131,16 @@ struct cmd_list_element *thread_cmd_list = NULL;
 
 static const struct internalvar_funcs thread_funcs =
 {
-  thread_id_make_value,
+  thread_id_per_inf_num_make_value,
+  NULL,
+  NULL
+};
+
+/* Implementation of `gthread' variable.  */
+
+static const struct internalvar_funcs gthread_funcs =
+{
+  global_thread_id_make_value,
   NULL,
   NULL
 };
@@ -2162,6 +2198,7 @@ Show printing of thread events (such as thread start and exit)."), NULL,
          &setprintlist, &showprintlist);
 
   create_internalvar_type_lazy ("_thread", &thread_funcs, NULL);
+  create_internalvar_type_lazy ("_gthread", &gthread_funcs, NULL);
 
   observer_attach_thread_ptid_changed (restore_current_thread_ptid_changed);
 }