[PATCH] PR gdb/21698: Fix synchronization problems under python interface

[Hsiangkai Wang <Hsiangkai at gmail dot com>]

When executing multiple steppings through gdb.post_event(), prompt will
show first and current_ui->prompt_state will be changed to PROMPTED.
There is no chance to switch prompt_state to PROMPT_NEEDED or
PROMPT_BLOCK.  So, synchronous commands will behave like asynchronous
commands under gdb.post_event().  In addition, GDB will raise an
exception while checking thread state in ensure_not_running() and GDB
will hang.

I propose a solution to initialize current_ui->prompt_state to
PROMPT_NEEDED in execute_gdb_command() to ensure synchronous commands
will behave as expected.

gdb/ChangeLog
2017-09-03  Hsiangkai Wang  <hsiangkai@gmail.com>

	PR gdb/21698
	* python/python.c (execute_gdb_command): Initialize prompt_state.

testsuite/ChangeLog
2017-09-03  Hsiangkai Wang  <Hsiangkai@gmail.com>

	PR gdb/21698
	* gdb.python/python.exp: Test multiple synchronous stepping
	through gdb.post_event().
	* gdb.python/step.py: New file.
---
 gdb/ChangeLog                       |  5 +++++
 gdb/python/python.c                 |  1 +
 gdb/testsuite/ChangeLog             |  7 +++++++
 gdb/testsuite/gdb.python/python.exp | 23 +++++++++++++++++++++++
 gdb/testsuite/gdb.python/step.py    |  7 +++++++
 5 files changed, 43 insertions(+)
 create mode 100644 gdb/testsuite/gdb.python/step.py

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 71566bd..7713b2f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-03  Hsiangkai Wang  <hsiangkai@gmail.com>
+
+	PR gdb/21698
+	* python/python.c (execute_gdb_command): Initialize prompt_state.
+
 2017-09-03  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* target/waitstatus.h (target_waitstatus_to_string): Change
diff --git a/gdb/python/python.c b/gdb/python/python.c
index c53e10f..49b5eff 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -589,6 +589,7 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
       struct interp *interp;
 
       scoped_restore save_async = make_scoped_restore (&current_ui->async, 0);
+      current_ui->prompt_state = PROMPT_NEEDED;
 
       scoped_restore save_uiout = make_scoped_restore (&current_uiout);
 
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index c15743b..1c1b75b 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2017-09-03  Hsiangkai Wang  <Hsiangkai@gmail.com>
+
+	PR gdb/21698
+	* gdb.python/python.exp: Test multiple synchronous stepping
+	through gdb.post_event().
+	* gdb.python/step.py: New file.
+
 2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* gdb.base/share-env-with-gdbserver.c: New file.
diff --git a/gdb/testsuite/gdb.python/python.exp b/gdb/testsuite/gdb.python/python.exp
index de8daad..6f46786 100644
--- a/gdb/testsuite/gdb.python/python.exp
+++ b/gdb/testsuite/gdb.python/python.exp
@@ -32,6 +32,9 @@ gdb_reinitialize_dir $srcdir/$subdir
 
 set remote_source2_py [gdb_remote_download host \
 			   ${srcdir}/${subdir}/source2.py]
+set remote_step_py [gdb_remote_download host \
+			   ${srcdir}/${subdir}/step.py]
+
 
 # Do this instead of the skip_python_check.
 # We want to do some tests when Python is not present.
@@ -474,3 +477,23 @@ gdb_py_test_silent_cmd "step" "Step into func2" 1
 gdb_py_test_silent_cmd "up" "Step out of func2" 1
 
 gdb_test "python print (gdb.find_pc_line(gdb.selected_frame().pc()).line > line)" "True" "test find_pc_line with resume address"
+
+# Start with a fresh gdb.
+clean_restart ${testfile}
+
+# The following tests require execution.
+
+if ![runto_main] then {
+    fail "can't run to main"
+    return 0
+}
+
+send_gdb "source $remote_step_py\n"
+gdb_expect {
+    -re ".*${gdb_prompt}.*Stepping successful" {
+        pass "multiple stepping in python script through post_event()"
+    }
+    timeout {
+        fail "multiple stepping in python script through post_event()"
+    }
+}
diff --git a/gdb/testsuite/gdb.python/step.py b/gdb/testsuite/gdb.python/step.py
new file mode 100644
index 0000000..c8cb866
--- /dev/null
+++ b/gdb/testsuite/gdb.python/step.py
@@ -0,0 +1,7 @@
+def test_steps():
+    for _ in range(6):
+        gdb.execute("si")
+
+    print("Stepping successful.")
+
+gdb.post_event(test_steps)
-- 
2.7.4