rundown.c

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#include "../../includes/me.h"
 
#define TEARDOWN_ACTIVE (1ULL << 63)
#define REFERENCE_COUNT (0x7FFFFFFFFFFFFFFF)
 
bool 
MsAcquireRundownProtection (
    IN    PRUNDOWN_REF rundown
) 
 
/*++
 
    Routine description : Safely acquires rundown protection on a shared resource to prevent it from being deleted or "rundown" while in use.
 
    Arguments:
 
        Pointer to RUNDOWN_REF Object.
 
    Return Values:
 
        True - The rundown protection acquisition has succeeded, the object is safe from memory deletion.
        False - Teardown has started on the object, handle gracefully.
 
--*/
 
{
    uint64_t old_count, new_count;
    do {
        old_count = rundown->Count;
        if (old_count & TEARDOWN_ACTIVE) {
            // Teardown has started, refuse to acquire.
            return false;
        }
        new_count = old_count + 1;
    } while (!InterlockedCompareExchangeU64(&rundown->Count, new_count, old_count));
    return true;
}
 
void 
MsReleaseRundownProtection (
    IN    PRUNDOWN_REF rundown
) 
 
/*++
 
    Routine description : Releases rundown protection from the object.
 
    Arguments:
 
        Pointer to RUNDOWN_REF Object.
 
    Return Values:
 
        None.
 
--*/
 
{
    InterlockedDecrementU64(&rundown->Count);
}
 
// Wait for rundown (teardown)
void MsWaitForRundownProtectionRelease (
    IN    PRUNDOWN_REF rundown
) 
 
/*++
 
    Routine description : Waits until all rundown protections have been released from the object, then starts Teardown.
    Use this when you want to gurantee an object will not be used after free.
 
    Arguments:
 
        Pointer to RUNDOWN_REF Object.
 
    Return Values:
 
        None.
 
--*/
 
{
    uint64_t old_count;
    do {
        old_count = rundown->Count;
    } while (!InterlockedCompareExchangeU64(&rundown->Count, old_count | TEARDOWN_ACTIVE, old_count));
 
    // Spin until count reaches zero (TODO RUNDOWN REF WAKE SLEEP (use the 0-62 bits for a pointer )
    while ((rundown->Count & REFERENCE_COUNT) != 0) {
        __pause();
    }
}