RTEMS | C++ std::mutex has no error checks (#5641)

[Amar Takhar (@amar)]

Amar Takhar commented: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5641#note_154343


Here are my results.

```shell
FreeBSD clang version 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)
Target: x86_64-unknown-freebsd15.0
```

```shell
# c++ -Wall -g -o lock -lpthread lock.cpp
# ./lock 
locking test
main: m1 at0x820d4a6b0
main: lock: m1
t1: unlock: m at 0x820d4a6b0
Illegal instruction        (core dumped) ./lock
```

```shell
(gdb) thread apply all bt

Thread 2 (LWP 810125):
#0  _nanosleep () at _nanosleep.S:4
#1  0x000000082232923c in __thr_nanosleep (time_to_sleep=0x820d4a598, time_remaining=0x820d4a598) at /usr/src/lib/libthr/thread/thr_syscalls.c:283
#2  0x00000008233b264b in std::__1::__libcpp_thread_sleep_for[abi:se190107](std::__1::chrono::duration<long long, std::__1::ratio<1l, 1000000000l> > const&) (__ns=...) at /usr/src/contrib/llvm-project/libcxx/include/__thread/support/pthread.h:198
#3  std::__1::this_thread::sleep_for (ns=...) at /usr/src/contrib/llvm-project/libcxx/src/thread.cpp:94
#4  0x0000000000204008 in std::__1::this_thread::sleep_for[abi:se190107]<long long, std::__1::ratio<1l, 1l> >(std::__1::chrono::duration<long long, std::__1::ratio<1l, 1l> > const&) (__d=...) at /usr/include/c++/v1/__thread/this_thread.h:48
#5  0x0000000000203b9c in main () at lock.cpp:25

Thread 1 (LWP 965367):
#0  0x00000008233a440f in __clang_trap_msg$libc++$/usr/src/contrib/llvm-project/libcxx/src/mutex.cpp:40: assertion ec == 0 failed: call to mutex::unlock failed. A possible reason is that the mutex wasn't locked
 () at /usr/src/contrib/llvm-project/libcxx/src/mutex.cpp:41
#1  std::__1::mutex::unlock (this=<optimized out>) at /usr/src/contrib/llvm-project/libcxx/src/mutex.cpp:39
#2  0x0000000000203a7e in t1_body (m=...) at lock.cpp:9
#3  0x000000000020509d in std::__1::__invoke[abi:se190107]<void (*)(std::__1::mutex&), std::__1::reference_wrapper<std::__1::mutex> >(void (*&&)(std::__1::mutex&), std::__1::reference_wrapper<std::__1::mutex>&&) (__f=@0xf1cd140b028: 0x203a20 <t1_body(std::__1::mutex&)>, __args=...) at /usr/include/c++/v1/__type_traits/invoke.h:150
#4  0x000000000020501e in std::__1::__thread_execute[abi:se190107]<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (*)(std::__1::mutex&), std::__1::reference_wrapper<std::__1::mutex>, 2ul>(std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (*)(std::__1::mutex&), std::__1::reference_wrapper<std::__1::mutex> >&, std::__1::__tuple_indices<2ul>) (__t=...) at /usr/include/c++/v1/__thread/thread.h:192
#5  0x0000000000204b9c in std::__1::__thread_proxy[abi:se190107]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (*)(std::__1::mutex&), std::__1::reference_wrapper<std::__1::mutex> > >(void*) (__vp=0xf1cd140b020) at /usr/include/c++/v1/__thread/thread.h:201
#6  0x000000082231dd21 in thread_start (curthread=0xf1cd1044810) at /usr/src/lib/libthr/thread/thr_create.c:299
#7  0x0000000000000000 in ?? ()
Backtrace stopped: Cannot access memory at address 0x828a94000
```

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5641#note_154343
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