Useful for debugging.
Motivation: With SMP on x64 I found a number of instances where critical sections would be left abandoned, causing lockups. From what I can tell it was exceptions inside rpcrt4, which leave the process in a blocked state. Might or might not be related to x64 / SMP.
For real value, you still need to put checks at certain places manually, but this is not super straight forward, because there can be false positives, e.g. when a process is terminated due to an exception, where the abandoned lock is acceptable, and we have this during testing. It's difficult to 100% distinguish this from silent and very bad lock leaks.
Problematic code:
__try
{
SomeFunction(); // throws an exception with a CS held, e.g. heap code
}
__except(1)
{
DPRINT1("Oops. let's just pretend it's all ok!\n");
}
RTL restrictions:
ExAllocatePool (and friends) must be used exclusively. RtlAllocateHeap (and friends) must NOT be used! ExAllocatePool (and friends) translate to RtlAllocateHeap (and friends) in ntdll\rtl\libsupp.c.
RtlEnterCriticalSection (and friends) must be used exclusively. ExAcquireFastMutex (and friends) must NOT be used! RtlEnterCriticalSection (and friends) translate to ExAcquireFastMutex (and friends) in ntoskrnl\rtl\libsupp.c. This means that RtlEnterCriticalSection (and friends) can NOT be used recursively in RTL. The reason for choosing RtlEnterCriticalSection (and friends) over ExAcquireFastMutex (and friends) is that the FAST_MUTEX struct is smaller than the RTL_CRITICAL_SECTION struct.
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