[PATCH v3 2/4] dts: add context manager for interactive shells

[jspewock@iol.unh.edu]

From: Jeremy Spewock <jspewock@iol.unh.edu>

Interactive shells are managed in a way currently where they are closed
and cleaned up at the time of garbage collection. Due to there being no
guarantee of when this garbage collection happens in Python, there is no
way to consistently know when an application will be closed without
manually closing the application yourself when you are done with it.
This doesn't cause a problem in cases where you can start another
instance of the same application multiple times on a server, but this
isn't the case for primary applications in DPDK. The introduction of
primary applications, such as testpmd, adds a need for knowing previous
instances of the application have been stopped and cleaned up before
starting a new one, which the garbage collector does not provide.

To solve this problem, a new class is added which acts as a wrapper
around the interactive shell that enforces that instances of the
application be managed using a context manager. Using a context manager
guarantees that once you leave the scope of the block where the
application is being used for any reason, the application will be closed
immediately. This avoids the possibility of the shell not being closed
due to an exception being raised or user error.

depends-on: patch-139227 ("dts: skip test cases based on capabilities")

Signed-off-by: Jeremy Spewock <jspewock@iol.unh.edu>
---
 .../critical_interactive_shell.py             | 93 +++++++++++++++++++
 .../remote_session/interactive_shell.py       | 13 ++-
 dts/framework/remote_session/testpmd_shell.py | 13 ++-
 dts/framework/testbed_model/sut_node.py       |  8 +-
 dts/tests/TestSuite_pmd_buffer_scatter.py     | 28 +++---
 dts/tests/TestSuite_smoke_tests.py            |  3 +-
 6 files changed, 134 insertions(+), 24 deletions(-)
 create mode 100644 dts/framework/remote_session/critical_interactive_shell.py

diff --git a/dts/framework/remote_session/critical_interactive_shell.py b/dts/framework/remote_session/critical_interactive_shell.py
new file mode 100644
index 0000000000..26bd891267
--- /dev/null
+++ b/dts/framework/remote_session/critical_interactive_shell.py
@@ -0,0 +1,93 @@
+r"""Wrapper around :class:`~.interactive_shell.InteractiveShell` that handles critical applications.
+
+Critical applications are defined as applications that require explicit clean-up before another
+instance of some application can be started. In DPDK these are referred to as "primary
+applications" and these applications take out a lock which stops other primary applications from
+running. Much like :class:`~.interactive_shell.InteractiveShell`\s,
+:class:`CriticalInteractiveShell` is meant to be extended by subclasses that implement application
+specific functionality and should never be instantiated directly.
+"""
+
+from typing import Callable
+
+from paramiko import SSHClient  # type: ignore[import]
+from typing_extensions import Self
+
+from framework.logger import DTSLogger
+from framework.settings import SETTINGS
+
+from .interactive_shell import InteractiveShell
+
+
+class CriticalInteractiveShell(InteractiveShell):
+    """The base class for interactive critical applications.
+
+    This class is a wrapper around :class:`~.interactive_shell.InteractiveShell` and should always
+    implement the exact same functionality with the primary difference being how the application
+    is started and stopped. In contrast to normal interactive shells, this class does not start the
+    application upon initialization of the class. Instead, the application is handled through a
+    context manager. This allows for more explicit starting and stopping of the application, and
+    more guarantees for when the application is cleaned up which are not present with normal
+    interactive shells that get cleaned up upon garbage collection.
+    """
+
+    _get_privileged_command: Callable[[str], str] | None
+
+    def __init__(
+        self,
+        interactive_session: SSHClient,
+        logger: DTSLogger,
+        get_privileged_command: Callable[[str], str] | None,
+        app_args: str = "",
+        timeout: float = SETTINGS.timeout,
+    ) -> None:
+        """Store parameters for creating an interactive shell, but do not start the application.
+
+        Note that this method also does not create the channel for the application, as this is
+        something that isn't needed until the application starts.
+
+        Args:
+            interactive_session: The SSH session dedicated to interactive shells.
+            logger: The logger instance this session will use.
+            get_privileged_command: A method for modifying a command to allow it to use
+                elevated privileges. If :data:`None`, the application will not be started
+                with elevated privileges.
+            app_args: The command line arguments to be passed to the application on startup.
+            timeout: The timeout used for the SSH channel that is dedicated to this interactive
+                shell. This timeout is for collecting output, so if reading from the buffer
+                and no output is gathered within the timeout, an exception is thrown. The default
+                value for this argument may be modified using the :option:`--timeout` command-line
+                argument or the :envvar:`DTS_TIMEOUT` environment variable.
+        """
+        self._interactive_session = interactive_session
+        self._logger = logger
+        self._timeout = timeout
+        self._app_args = app_args
+        self._get_privileged_command = get_privileged_command
+
+    def __enter__(self) -> Self:
+        """Enter the context block.
+
+        Upon entering a context block with this class, the desired behavior is to create the
+        channel for the application to use, and then start the application.
+
+        Returns:
+            Reference to the object for the application after it has been started.
+        """
+        self._init_channel()
+        self._start_application(self._get_privileged_command)
+        return self
+
+    def __exit__(self, *_) -> None:
+        """Exit the context block.
+
+        Upon exiting a context block with this class, we want to ensure that the instance of the
+        application is explicitly closed and properly cleaned up using its close method. Note that
+        because this method returns :data:`None` if an exception was raised within the block, it is
+        not handled and will be re-raised after the application is closed.
+
+        The desired behavior is to close the application regardless of the reason for exiting the
+        context and then recreate that reason afterwards. All method arguments are ignored for
+        this reason.
+        """
+        self.close()
diff --git a/dts/framework/remote_session/interactive_shell.py b/dts/framework/remote_session/interactive_shell.py
index 921c73d9df..6dee7ebce0 100644
--- a/dts/framework/remote_session/interactive_shell.py
+++ b/dts/framework/remote_session/interactive_shell.py
@@ -89,16 +89,19 @@ def __init__(
                 and no output is gathered within the timeout, an exception is thrown.
         """
         self._interactive_session = interactive_session
-        self._ssh_channel = self._interactive_session.invoke_shell()
-        self._stdin = self._ssh_channel.makefile_stdin("w")
-        self._stdout = self._ssh_channel.makefile("r")
-        self._ssh_channel.settimeout(timeout)
-        self._ssh_channel.set_combine_stderr(True)  # combines stdout and stderr streams
         self._logger = logger
         self._timeout = timeout
         self._app_args = app_args
+        self._init_channel()
         self._start_application(get_privileged_command)
 
+    def _init_channel(self):
+        self._ssh_channel = self._interactive_session.invoke_shell()
+        self._stdin = self._ssh_channel.makefile_stdin("w")
+        self._stdout = self._ssh_channel.makefile("r")
+        self._ssh_channel.settimeout(self._timeout)
+        self._ssh_channel.set_combine_stderr(True)  # combines stdout and stderr streams
+
     def _start_application(self, get_privileged_command: Callable[[str], str] | None) -> None:
         """Starts a new interactive application based on the path to the app.
 
diff --git a/dts/framework/remote_session/testpmd_shell.py b/dts/framework/remote_session/testpmd_shell.py
index 284412e82c..ca30aac264 100644
--- a/dts/framework/remote_session/testpmd_shell.py
+++ b/dts/framework/remote_session/testpmd_shell.py
@@ -26,7 +26,7 @@
 from framework.settings import SETTINGS
 from framework.utils import StrEnum
 
-from .interactive_shell import InteractiveShell
+from .critical_interactive_shell import CriticalInteractiveShell
 
 
 class TestPmdDevice(object):
@@ -82,7 +82,7 @@ class TestPmdForwardingModes(StrEnum):
     recycle_mbufs = auto()
 
 
-class TestPmdShell(InteractiveShell):
+class TestPmdShell(CriticalInteractiveShell):
     """Testpmd interactive shell.
 
     The testpmd shell users should never use
@@ -253,6 +253,15 @@ def get_capas_rxq(
                 else:
                     unsupported_capabilities.add(NicCapability.scattered_rx)
 
+    def __exit__(self, *_) -> None:
+        """Overrides :meth:`~.critical_interactive_shell.CriticalInteractiveShell.__exit__`.
+
+        Ensures that when the context is exited packet forwarding is stopped before closing the
+        application.
+        """
+        self.stop()
+        super().__exit__()
+
 
 class NicCapability(Enum):
     """A mapping between capability names and the associated :class:`TestPmdShell` methods.
diff --git a/dts/framework/testbed_model/sut_node.py b/dts/framework/testbed_model/sut_node.py
index 1fb536735d..7dd39fd735 100644
--- a/dts/framework/testbed_model/sut_node.py
+++ b/dts/framework/testbed_model/sut_node.py
@@ -243,10 +243,10 @@ def get_supported_capabilities(
         unsupported_capas: set[NicCapability] = set()
         self._logger.debug(f"Checking which capabilities from {capabilities} NIC are supported.")
         testpmd_shell = self.create_interactive_shell(TestPmdShell, privileged=True)
-        for capability in capabilities:
-            if capability not in supported_capas or capability not in unsupported_capas:
-                capability.value(testpmd_shell, supported_capas, unsupported_capas)
-        del testpmd_shell
+        with testpmd_shell as running_testpmd:
+            for capability in capabilities:
+                if capability not in supported_capas or capability not in unsupported_capas:
+                    capability.value(running_testpmd, supported_capas, unsupported_capas)
         return supported_capas
 
     def _set_up_build_target(self, build_target_config: BuildTargetConfiguration) -> None:
diff --git a/dts/tests/TestSuite_pmd_buffer_scatter.py b/dts/tests/TestSuite_pmd_buffer_scatter.py
index 3701c47408..41f6090a7e 100644
--- a/dts/tests/TestSuite_pmd_buffer_scatter.py
+++ b/dts/tests/TestSuite_pmd_buffer_scatter.py
@@ -101,7 +101,7 @@ def pmd_scatter(self, mbsize: int) -> None:
         Test:
             Start testpmd and run functional test with preset mbsize.
         """
-        testpmd = self.sut_node.create_interactive_shell(
+        testpmd_shell = self.sut_node.create_interactive_shell(
             TestPmdShell,
             app_parameters=(
                 "--mbcache=200 "
@@ -112,17 +112,21 @@ def pmd_scatter(self, mbsize: int) -> None:
             ),
             privileged=True,
         )
-        testpmd.set_forward_mode(TestPmdForwardingModes.mac)
-        testpmd.start()
-
-        for offset in [-1, 0, 1, 4, 5]:
-            recv_payload = self.scatter_pktgen_send_packet(mbsize + offset)
-            self._logger.debug(f"Payload of scattered packet after forwarding: \n{recv_payload}")
-            self.verify(
-                ("58 " * 8).strip() in recv_payload,
-                f"Payload of scattered packet did not match expected payload with offset {offset}.",
-            )
-        testpmd.stop()
+        with testpmd_shell as testpmd:
+            testpmd.set_forward_mode(TestPmdForwardingModes.mac)
+            testpmd.start()
+
+            for offset in [-1, 0, 1, 4, 5]:
+                recv_payload = self.scatter_pktgen_send_packet(mbsize + offset)
+                self._logger.debug(
+                    f"Payload of scattered packet after forwarding: \n{recv_payload}"
+                )
+                self.verify(
+                    ("58 " * 8).strip() in recv_payload,
+                    "Payload of scattered packet did not match expected payload with offset "
+                    f"{offset}.",
+                )
+            testpmd.stop()
 
     def test_scatter_mbuf_2048(self) -> None:
         """Run the :meth:`pmd_scatter` test with `mbsize` set to 2048."""
diff --git a/dts/tests/TestSuite_smoke_tests.py b/dts/tests/TestSuite_smoke_tests.py
index a553e89662..360e64eb5a 100644
--- a/dts/tests/TestSuite_smoke_tests.py
+++ b/dts/tests/TestSuite_smoke_tests.py
@@ -100,7 +100,8 @@ def test_devices_listed_in_testpmd(self) -> None:
             List all devices found in testpmd and verify the configured devices are among them.
         """
         testpmd_driver = self.sut_node.create_interactive_shell(TestPmdShell, privileged=True)
-        dev_list = [str(x) for x in testpmd_driver.get_devices()]
+        with testpmd_driver as testpmd:
+            dev_list = [str(x) for x in testpmd.get_devices()]
         for nic in self.nics_in_node:
             self.verify(
                 nic.pci in dev_list,
-- 
2.45.1