bool performTryPutMVar()

in rts/Threads.c [738:809]

• 50 lines of code
• 9 McCabe index (conditional complexity)

bool performTryPutMVar(Capability *cap, StgMVar *mvar, StgClosure *value)
{
    const StgInfoTable *info;
    StgMVarTSOQueue *q;
    StgTSO *tso;

    info = lockClosure((StgClosure*)mvar);

    if (mvar->value != &stg_END_TSO_QUEUE_closure) {
#if defined(THREADED_RTS)
        unlockClosure((StgClosure*)mvar, info);
#endif
        return false;
    }

    q = mvar->head;
loop:
    if (q == (StgMVarTSOQueue*)&stg_END_TSO_QUEUE_closure) {
        /* No further takes, the MVar is now full. */
        if (info == &stg_MVAR_CLEAN_info) {
            dirty_MVAR(&cap->r, (StgClosure*)mvar);
        }

        mvar->value = value;
        unlockClosure((StgClosure*)mvar, &stg_MVAR_DIRTY_info);
        return true;
    }
    if (q->header.info == &stg_IND_info ||
        q->header.info == &stg_MSG_NULL_info) {
        q = (StgMVarTSOQueue*)((StgInd*)q)->indirectee;
        goto loop;
    }

    // There are takeMVar(s) waiting: wake up the first one
    tso = q->tso;
    mvar->head = q->link;
    if (mvar->head == (StgMVarTSOQueue*)&stg_END_TSO_QUEUE_closure) {
        mvar->tail = (StgMVarTSOQueue*)&stg_END_TSO_QUEUE_closure;
    }

    ASSERT(tso->block_info.closure == (StgClosure*)mvar);
    // save why_blocked here, because waking up the thread destroys
    // this information
    StgWord why_blocked = tso->why_blocked;

    // actually perform the takeMVar
    StgStack* stack = tso->stackobj;
    stack->sp[1] = (W_)value;
    stack->sp[0] = (W_)&stg_ret_p_info;

    // indicate that the MVar operation has now completed.
    tso->_link = (StgTSO*)&stg_END_TSO_QUEUE_closure;

    if (stack->dirty == 0) {
        dirty_STACK(cap, stack);
    }

    tryWakeupThread(cap, tso);

    // If it was a readMVar, then we can still do work,
    // so loop back. (XXX: This could take a while)
    if (why_blocked == BlockedOnMVarRead) {
        q = ((StgMVarTSOQueue*)q)->link;
        goto loop;
    }

    ASSERT(why_blocked == BlockedOnMVar);

    unlockClosure((StgClosure*)mvar, info);

    return true;
}