futex_map.cc

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/*
 * Copyright (c) 2017 Advanced Micro Devices, Inc.
 * All rights reserved.
 *
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 * met: redistributions of source code must retain the above copyright
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 * redistributions in binary form must reproduce the above copyright
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 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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#include <sim/futex_map.hh>
 
namespace gem5
{
 
FutexKey::FutexKey(uint64_t addr_in, uint64_t tgid_in)
        : addr(addr_in), tgid(tgid_in) {}
 
bool
FutexKey::operator==(const FutexKey &in) const
{
    return addr == in.addr && tgid == in.tgid;
}
 
WaiterState::WaiterState(ThreadContext* _tc, int _bitmask)
      : tc(_tc), bitmask(_bitmask) { }
 
bool
WaiterState::checkMask(int wakeup_bitmask) const
{
    return bitmask & wakeup_bitmask;
}
 
void
FutexMap::suspend(Addr addr, uint64_t tgid, ThreadContext *tc)
{
    suspend_bitset(addr, tgid, tc, 0xffffffff);
}
 
int
FutexMap::wakeup(Addr addr, uint64_t tgid, int count)
{
    FutexKey key(addr, tgid);
    auto it = find(key);
 
    if (it == end())
        return 0;
 
    int woken_up = 0;
    auto &waiterList = it->second;
 
    while (!waiterList.empty() && woken_up < count) {
        // Threads may be woken up by access to locked
        // memory addresses outside of syscalls, so we
        // must only count threads that were actually
        // woken up by this syscall.
        auto& tc = waiterList.front().tc;
        tc->activate();
        woken_up++;
        waiterList.pop_front();
        waitingTcs.erase(tc);
    }
 
    if (waiterList.empty())
        erase(it);
 
    return woken_up;
}
 
void
FutexMap::suspend_bitset(Addr addr, uint64_t tgid, ThreadContext *tc,
               int bitmask)
{
    FutexKey key(addr, tgid);
    auto it = find(key);
 
    if (it == end()) {
        WaiterList waiterList {WaiterState(tc, bitmask)};
        insert({key, waiterList});
    } else {
        it->second.push_back(WaiterState(tc, bitmask));
    }
    waitingTcs.emplace(tc);
 
    tc->suspend();
}
 
int
FutexMap::wakeup_bitset(Addr addr, uint64_t tgid, int bitmask)
{
    FutexKey key(addr, tgid);
    auto it = find(key);
 
    if (it == end())
        return 0;
 
    int woken_up = 0;
 
    auto &waiterList = it->second;
    auto iter = waiterList.begin();
 
    while (iter != waiterList.end()) {
        WaiterState& waiter = *iter;
 
        if (waiter.checkMask(bitmask)) {
            waiter.tc->activate();
            waitingTcs.erase(waiter.tc);
            iter = waiterList.erase(iter);
            woken_up++;
        } else {
            ++iter;
        }
    }
 
    if (waiterList.empty())
        erase(it);
 
    return woken_up;
}
 
int
FutexMap::requeue(Addr addr1, uint64_t tgid, int count, int count2, Addr addr2)
{
    FutexKey key1(addr1, tgid);
    auto it1 = find(key1);
 
    if (it1 == end())
        return 0;
 
    int woken_up = 0;
    auto &waiterList1 = it1->second;
 
    while (!waiterList1.empty() && woken_up < count) {
        waiterList1.front().tc->activate();
        waiterList1.pop_front();
        woken_up++;
    }
 
    WaiterList tmpList;
    int requeued = 0;
 
    while (!waiterList1.empty() && requeued < count2) {
      auto w = waiterList1.front();
      waiterList1.pop_front();
      tmpList.push_back(w);
      requeued++;
    }
 
    FutexKey key2(addr2, tgid);
    auto it2 = find(key2);
 
    if (it2 == end() && requeued > 0) {
        insert({key2, tmpList});
    } else {
        it2->second.insert(it2->second.end(),
                           tmpList.begin(), tmpList.end());
    }
 
    if (waiterList1.empty())
        erase(it1);
 
    return woken_up + requeued;
}
 
bool
FutexMap::is_waiting(ThreadContext *tc)
{
    return waitingTcs.find(tc) != waitingTcs.end();
}
 
} // namespace gem5