| 90f8d9b4 | 13-Mar-2023 |
Hannu Lounento <hannu.lounento@vaisala.com> |
Allow propagating exceptions from server methods
sdbusplus calls the D-Bus method implementation functions in such a way
that the callstack contains sd_bus C functions from libsystemd, and
sdbusplus
Allow propagating exceptions from server methods
sdbusplus calls the D-Bus method implementation functions in such a way
that the callstack contains sd_bus C functions from libsystemd, and
sdbusplus only catches the specific exceptions that match the errors
defined for the D-Bus method before returning execution to the C
functions. If any D-Bus method implementation propagates any other
exception than the errors the method declares, the C functions in the
callstack may leak resources.
There isn't any documentation or other statement that would prohibit
exceptions from being thrown / propagated from method implementations.
This seems to be a known issue though [1]:
By throwing an exception, you're not making an error return to the
calling client, but instead blowing through all of the `sd_bus` C
code with your C++ exception and putting your application into an
invalid state. At a minimum you are leaking memory.
Thus, catch any exceptions propagated from method implementations and
re-throw them from sdbusplus::bus::bus::process*().
Catching and re-throwing avoids resource leaks from sd_bus C functions.
And as a consequence it would allow propagating exceptions in the normal
way until the caller that is prepared to handle them -- ultimately even
up to main(). Propagating exceptions to `main()` allows for terminating
the process in a controlled fashion in case unexpected failures, which,
in turn, allows for a chance to recover from potential failures modes
that persist until application restart (e.g. due to some invalid state
stored in RAM).
Also, terminating the application, in which case the D-Bus daemon
returns the standard error org.freedesktop.DBus.Error.NoReply to the
client, avoids the need to declare an error for internal failures in the
D-Bus API. Internal errors in API add little value over
org.freedesktop.DBus.Error.NoReply and bloat the API as clients many
times can't handle them in any better way than
org.freedesktop.DBus.Error.NoReply.
Only std::exceptions are catched (i.e. not `catch (...)`) and propagated
to keep the implementation simple. The assumption is that only
exceptions (i.e. classes derived from std::exception) are used for
reporting errors.
Tested: With the calculator example changed to throw an unexpected exception:
From 914e045d1f92a1730d32f84ac7a74cd867c76760 Mon Sep 17 00:00:00 2001
From: Hannu Lounento <hannu.lounento@vaisala.com>
Date: Mon, 13 Mar 2023 15:53:17 +0200
Subject: [PATCH] [dbg] Add a propagating exception to the calculator example
Not to be merged to sdbusplus master but only for RFC / demonstration
purposes.
Can be triggered by commands like
busctl --user call net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator Clear
busctl --user get-property net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator LastResult
busctl --user set-property net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator LastResult x 1
Change-Id: Ie9f47227afe7e0fa9765c602bec987aea71b9b86
Signed-off-by: Hannu Lounento <hannu.lounento@vaisala.com>
---
example/calculator-server.cpp | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)
diff --git a/example/calculator-server.cpp b/example/calculator-server.cpp
index aa60662..eba9cc0 100644
--- a/example/calculator-server.cpp
+++ b/example/calculator-server.cpp
@@ -3,6 +3,7 @@
#include <net/poettering/Calculator/server.hpp>
#include <sdbusplus/server.hpp>
+#include <cstdlib>
#include <iostream>
#include <string_view>
@@ -42,10 +43,22 @@ struct Calculator : Calculator_inherit
/** Clear lastResult, broadcast 'Cleared' signal */
void clear() override
{
- auto v = lastResult();
- lastResult(0);
- cleared(v);
- return;
+ throw std::runtime_error{"A propagating exception"};
+ }
+
+ int64_t lastResult() const override
+ {
+ throw std::runtime_error{"A propagating exception"};
+ }
+
+ int64_t lastResult(int64_t /*value*/, bool /*skipSignal*/) override
+ {
+ throw std::runtime_error{"A propagating exception"};
+ }
+
+ int64_t lastResult(int64_t /*value*/) override
+ {
+ throw std::runtime_error{"A propagating exception"};
}
};
@@ -71,5 +84,13 @@ int main()
Calculator c1{b, path};
// Handle dbus processing forever.
- b.process_loop();
+ try
+ {
+ b.process_loop();
+ }
+ catch (const std::exception& e)
+ {
+ std::cerr << "Terminating due to a fatal condition: " << e.what() << std::endl;
+ return EXIT_FAILURE;
+ }
}
--
2.40.0
1) Built and executed unit tests:
sdbusplus$ rm -rf build/ && CXXFLAGS=-Wno-maybe-uninitialized meson setup build && cd build && ninja && ninja test
The Meson build system
Version: 0.62.2
Source dir: /path/to/sdbusplus
Build dir: /path/to/sdbusplus/build
Build type: native build
Project name: sdbusplus
Project version: 1.0.0
C compiler for the host machine: ccache cc (gcc 12.2.1 "cc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)")
C linker for the host machine: cc ld.bfd 2.37-37
C++ compiler for the host machine: ccache c++ (gcc 12.2.1 "c++ (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)")
C++ linker for the host machine: c++ ld.bfd 2.37-37
Host machine cpu family: x86_64
Host machine cpu: x86_64
Found pkg-config: /usr/bin/pkg-config (1.8.0)
Run-time dependency libsystemd found: YES 250
Program python3 (inflection, yaml, mako) found: YES (/usr/bin/python3) modules: inflection, yaml, mako
Run-time dependency Boost found: YES 1.76.0 (/usr)
Program sdbus++ found: YES (/path/to/sdbusplus/tools/sdbus++)
Program sdbus++ found: YES (overridden)
Program sdbus++-gen-meson found: YES (/path/to/sdbusplus/tools/sdbus++-gen-meson)
Program sdbus++-gen-meson found: YES (overridden)
Header <boost/asio.hpp> has symbol "boost::asio::io_context" : YES
Run-time dependency Boost (found: context, coroutine) found: YES 1.76.0 (/usr)
Run-time dependency GTest found: YES 1.11.0
Run-time dependency GMock found: YES 1.11.0
Build targets in project: 34
Found ninja-1.10.2 at /usr/bin/ninja
[77/77] Linking target example/calculator-client
[0/1] Running all tests.
1/21 test_async_task OK 0.03s
2/21 test_bus_list_names OK 0.02s
3/21 test_bus_match OK 0.02s
4/21 test_bus_exception OK 0.02s
5/21 test_exception_sdbus_error OK 0.02s
6/21 test_message_append OK 0.01s
7/21 test_message_native_types OK 0.01s
8/21 test_message_read OK 0.03s
9/21 test_message_types OK 0.02s
10/21 test_unpack_properties OK 0.02s
11/21 test_utility_tuple_to_array OK 0.02s
12/21 test_utility_type_traits OK 0.01s
13/21 test-bus_aio OK 0.01s
14/21 test-vtable OK 0.01s
15/21 test-server OK 0.01s
16/21 test-server-message-variant OK 0.01s
17/21 test_message_call OK 0.07s
18/21 test_event_event OK 0.31s
19/21 test_async_timer OK 0.51s
20/21 test_async_context OK 0.52s
21/21 test_timer OK 18.02s
Ok: 21
Expected Fail: 0
Fail: 0
Unexpected Pass: 0
Skipped: 0
Timeout: 0
[...]
-Wno-maybe-uninitialized was used because the current master
384943be7e81b08ed102abfaa3f2be2ad915e800 ("sdbus++: async: client: fix
client_t usage") failed to build with
In file included from /usr/include/gtest/internal/gtest-death-test-internal.h:39,
from /usr/include/gtest/gtest-death-test.h:41,
from /usr/include/gtest/gtest.h:64,
from /usr/include/gmock/internal/gmock-internal-utils.h:47,
from /usr/include/gmock/gmock-actions.h:145,
from /usr/include/gmock/gmock.h:59,
from ../include/sdbusplus/test/sdbus_mock.hpp:6,
from ../test/exception/sdbus_error.cpp:4:
In copy constructor ‘testing::internal::MatcherBase<T>::MatcherBase(const testing::internal::MatcherBase<T>&) [with T = sd_bus_error*]’,
inlined from ‘testing::Matcher<sd_bus_error*>::Matcher(const testing::Matcher<sd_bus_error*>&)’ at /usr/include/gtest/gtest-matchers.h:479:7,
inlined from ‘testing::internal::MockSpec<int(sd_bus_error*, int)> sdbusplus::SdBusMock::gmock_sd_bus_error_set_errno(const testing::Matcher<sd_bus_error*>&, const testing::Matcher<int>&)’ at ../include/sdbusplus/test/sdbus_mock.hpp:51:5,
inlined from ‘virtual void {anonymous}::SdBusError_NotSetErrno_Test::TestBody()’ at ../test/exception/sdbus_error.cpp:59:5:
/usr/include/gtest/gtest-matchers.h:302:33: error: ‘<unnamed>.testing::Matcher<sd_bus_error*>::<unnamed>.testing::internal::MatcherBase<sd_bus_error*>::buffer_’ may be used uninitialized [-Werror=maybe-uninitialized]
302 | : vtable_(other.vtable_), buffer_(other.buffer_) {
| ^~~~~~~~~~~~~~~~~~~~~~
on Fedora 36 with
$ gcc --version
gcc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)
and
$ dnf info gtest-devel
[...]
Name : gtest-devel
Version : 1.11.0
Release : 2.fc36
Architecture : x86_64
2) Verified no memory leaks were reported by Valgrind anymore:
sdbusplus/build$ valgrind --leak-check=full --show-leak-kinds=all ./example/calculator-server
==61886== Memcheck, a memory error detector
==61886== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==61886== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==61886== Command: ./example/calculator-server
==61886==
and called the throwing method:
build$ busctl --user call net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator Clear
Call failed: Remote peer disconnected
and verified the process terminates but produces no memory leaks:
Terminating due to a fatal condition: A propagating exception
==61886==
==61886== HEAP SUMMARY:
==61886== in use at exit: 0 bytes in 0 blocks
==61886== total heap usage: 143 allocs, 143 frees, 96,732 bytes allocated
==61886==
==61886== All heap blocks were freed -- no leaks are possible
==61886==
==61886== For lists of detected and suppressed errors, rerun with: -s
==61886== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Similarly reading the `LastResult` property:
build$ valgrind --leak-check=full --show-leak-kinds=all ./example/calculator-server
==36140== Memcheck, a memory error detector
==36140== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==36140== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==36140== Command: ./example/calculator-server
==36140==
build$ busctl --user get-property net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator LastResult
Failed to get property LastResult on interface net.poettering.Calculator: Remote peer disconnected
Terminating due to a fatal condition: A propagating exception
==36140==
==36140== HEAP SUMMARY:
==36140== in use at exit: 0 bytes in 0 blocks
==36140== total heap usage: 148 allocs, 148 frees, 96,992 bytes allocated
==36140==
==36140== All heap blocks were freed -- no leaks are possible
==36140==
==36140== For lists of detected and suppressed errors, rerun with: -s
==36140== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
and writing the property:
==36383== Memcheck, a memory error detector
==36383== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==36383== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==36383== Command: ./example/calculator-server
==36383==
build$ busctl --user set-property net.poettering.Calculator /net/poettering/calculator net.poettering.Calculator LastResult x 1
Terminating due to a fatal condition: A propagating exception
==36383==
==36383== HEAP SUMMARY:
==36383== in use at exit: 0 bytes in 0 blocks
==36383== total heap usage: 146 allocs, 146 frees, 97,010 bytes allocated
==36383==
==36383== All heap blocks were freed -- no leaks are possible
==36383==
==36383== For lists of detected and suppressed errors, rerun with: -s
==36383== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
[1] https://lore.kernel.org/openbmc/YTDvfIn4Z05mGdCx@heinlein/
Change-Id: I014099a91f526a92c0f6646e75b4029513ad19a8
Signed-off-by: Hannu Lounento <hannu.lounento@vaisala.com>
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