Cppguard

CppGuard is now part of https://github.com/JochenBaier/BugInsight

Purpose

CppGuard is developer tool for testing C++ applications made with Visual Studio for deadlocks and wrong lock usage. I can be used manually and within a CI system. CppGuard consists of the DLL cppguard.dll and the header cppguard.h.

CppGuard uses the deadlock detection algorithm from C++ library Abseil. This algorithm will detect a potential deadlock even if the executed program does not actually deadlock. It maintains an acquired-before graph and checks for cycles in this graph. The underlying graph algorithm is described here. There is no relationship between the Abseil project and CppGuard.

Advantages:

• Test applications that cannot be tested on Linux with ThreadSanitizer
• ThreadSanitizer often cannot cover 100% as some program parts are not portable: CppGuard covers this gap
• Test with the Windows operating system on which the program will later run
• Test applications that run too slowly with other Windows OS deadlock test tools
• Test C/C++ DLLs loaded in a Java program ( Java Native Interfaces)
• Test C/C++ DLLs loaded in a .Net program

Example deadlock detection:

If locks are acquired in inconsistent order, it depends on the timing whether a deadlock occur or not. Example with 2 threads and mutex a and b:

std::mutex a;
std::mutex b;

//lock order: a -> b
std::thread t1([&]() {
  const std::lock_guard<std::mutex> lock_a(a);
  const std::lock_guard<std::mutex> lock_b(b);
});

//lock order: b -> a
std::thread t2([&]() {
  const std::lock_guard<std::mutex> lock_b(b);
  const std::lock_guard<std::mutex> lock_a(a);
});

t1.join();
t2.join();

If t2 will acquired lock b after t1 has locked a and b no deadlock occur. if t1 got lock a and t2 got lock b a deadlock occur.

CppGuard has detected the potential deadlock:

==========================================================================================================
CppGuard: [Error] Potential deadlock at lock: 0x1e2599ebd0, thread ID: 50092.
Lock Call Stack:
C:\dev\cppguard\cppguard\deadlock_monitor.cpp(152,0): deadlock_monitor_t::dlc_deadlock_check_before_lock
C:\dev\cppguard\cppguard\api_monitors\mutex_monitor.cpp(37,0): cppguard_mtx_lock
...

A cycle in the historical lock ordering graph has been observed:

Thread ID: 50092
Holding lock: 0x1e2599ec40
Wait for lock: 0x1e2599ebd0
Call Stack:
C:\dev\cppguard\cppguard\api_monitors\mutex_monitor.cpp(37,0): cppguard_mtx_lock
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.38.33130\include\mutex(56,0): std::_Mutex_base::lock
...

Thread ID: 48624
Holding lock: 0x1e2599ebd0
Wait for lock: 0x1e2599ec40
Call Stack:
C:\dev\cppguard\cppguard\api_monitors\mutex_monitor.cpp(37,0): cppguard_mtx_lock
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.38.33130\include\mutex(56,0): std::_Mutex_base::lock
...

Features:

• Deadlock detection: A warning or an error is generated if potential deadlock (a cycle) is detected (from Abseil algorithm)

• Detect wrong lock usage: Detect locks which are released by threads which do no hold them (from Abseil algorithm)

• Lock watchdog: The time a lock is waiting for a lock or holding a lock is monitored and a log or error is created if a maximum time is exceeded

• Runs on Windows OS with the native lock APIs of Windows: Critical Section, std::mutex and std::recursive_mutex

• Test C/C++ DLLs loaded in a Java or a .Net programs

• Overhead depends on usage. Pretty good for IO bound applications (e.g. TCPI/IP based)

• Works with Debug, Release and RelWithDebInfo builds

• For basic usage no source code changes are needed. Minor changes (minimum 2 lines) to the build system (CMake, or Visual Studio Project) are needed

Quickstart and building

see Quickstart

Technical background:

CppGuard provides:

• cppguard.dll: This DLL and has to be linked to the project to test (import library: cppguard.lib)
• cppguard.h: This header file is automatically included in all source files using Visual Studio option Forced Include File. Macros like #define EnterCriticalSection(x) cppguard_enter_critical_section(x) will intercept the lock API call

Supported Lock APIs:

• InitializeCriticalSection(), EnterCriticalSection(), TryEnterCriticalSection(), LeaveCriticalSection(), DeleteCriticalSection()

• std::mutex, std::recursive_mutex: via internal functions from mutex header_Mtx_*()

• std::lock_guard, std::unique_lock

Not supported Lock APIs:

• Slim Reader/Writer (SRW) Locks: no DeleteSRWLock() provided, needed to track delete of lock

Not yet tested:

• std::scoped_lock, std::shared_mutex, std::timed_mutex, std::recursive_timed_mutex std::shared_timed_mutex

Options

see Options

Used Third-party software

see Third-party software

License

CppGuard is licensed under the terms of the Apache 2.0 license. See LICENSE for more information.