Export gdb.block_signals and create gdb.Thread

While working on an experiment, I realized that I needed the DAP
block_signals function.  I figured other developers may need it as
well, so this patch moves it from DAP to the gdb module and exports
it.

I also added a new subclass of threading.Thread that ensures that
signals are blocked in the new thread.

Finally, this patch slightly rearranges the documentation so that
gdb-side threading issues and functions are all discussed in a single
node.

2 files changed, 34 insertions, 24 deletions

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 6f3f194..98aadb1 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -13,6 +13,8 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import signal
+import threading
 import traceback
 import os
 import sys
@@ -259,3 +261,33 @@ def with_parameter(name, value):
         yield None
     finally:
         set_parameter(name, old_value)
+
+
+@contextmanager
+def blocked_signals():
+    """A helper function that blocks and unblocks signals."""
+    if not hasattr(signal, "pthread_sigmask"):
+        yield
+        return
+
+    to_block = {signal.SIGCHLD, signal.SIGINT, signal.SIGALRM, signal.SIGWINCH}
+    signal.pthread_sigmask(signal.SIG_BLOCK, to_block)
+    try:
+        yield None
+    finally:
+        signal.pthread_sigmask(signal.SIG_UNBLOCK, to_block)
+
+
+class Thread(threading.Thread):
+    """A GDB-specific wrapper around threading.Thread
+
+    This wrapper ensures that the new thread blocks any signals that
+    must be delivered on GDB's main thread."""
+
+    def start(self):
+        # GDB requires that these be delivered to the main thread.  We
+        # do this here to avoid any possible race with the creation of
+        # the new thread.  The thread mask is inherited by new
+        # threads.
+        with blocked_signals():
+            super().start()
diff --git a/gdb/python/lib/gdb/dap/startup.py b/gdb/python/lib/gdb/dap/startup.py
index aa834cd..15d1fb9 100644
--- a/gdb/python/lib/gdb/dap/startup.py
+++ b/gdb/python/lib/gdb/dap/startup.py
@@ -18,10 +18,8 @@
 import functools
 import gdb
 import queue
-import signal
 import threading
 import traceback
-from contextlib import contextmanager
 import sys
 
 
@@ -33,32 +31,12 @@ _gdb_thread = threading.current_thread()
 _dap_thread = None
 
 
-@contextmanager
-def blocked_signals():
-    """A helper function that blocks and unblocks signals."""
-    if not hasattr(signal, "pthread_sigmask"):
-        yield
-        return
-
-    to_block = {signal.SIGCHLD, signal.SIGINT, signal.SIGALRM, signal.SIGWINCH}
-    signal.pthread_sigmask(signal.SIG_BLOCK, to_block)
-    try:
-        yield None
-    finally:
-        signal.pthread_sigmask(signal.SIG_UNBLOCK, to_block)
-
-
 def start_thread(name, target, args=()):
     """Start a new thread, invoking TARGET with *ARGS there.
     This is a helper function that ensures that any GDB signals are
     correctly blocked."""
-    # GDB requires that these be delivered to the gdb thread.  We
-    # do this here to avoid any possible race with the creation of
-    # the new thread.  The thread mask is inherited by new
-    # threads.
-    with blocked_signals():
-        result = threading.Thread(target=target, args=args, daemon=True)
-        result.start()
+    result = gdb.Thread(target=target, args=args, daemon=True)
+    result.start()
 
 
 def start_dap(target):