text: //===-- sanitizer_deadlock_detector1.cpp ----------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // Deadlock detector implementation based on NxN adjacency bit matrix.
  //
  //===----------------------------------------------------------------------===//
  
  #include "sanitizer_deadlock_detector_interface.h"
  #include "sanitizer_deadlock_detector.h"
  #include "sanitizer_allocator_internal.h"
  #include "sanitizer_placement_new.h"
  #include "sanitizer_mutex.h"
  
  #if SANITIZER_DEADLOCK_DETECTOR_VERSION == 1
  
  namespace __sanitizer {
  
  typedef TwoLevelBitVector<> DDBV;  // DeadlockDetector's bit vector.
  
  struct DDPhysicalThread {
  };
  
  struct DDLogicalThread {
    u64 ctx;
    DeadlockDetectorTLS<DDBV> dd;
    DDReport rep;
    bool report_pending;
  };
  
  struct DD : public DDetector {
    SpinMutex mtx;
    DeadlockDetector<DDBV> dd;
    DDFlags flags;
  
    explicit DD(const DDFlags *flags);
  
    DDPhysicalThread *CreatePhysicalThread() override;
    void DestroyPhysicalThread(DDPhysicalThread *pt) override;
  
    DDLogicalThread *CreateLogicalThread(u64 ctx) override;
    void DestroyLogicalThread(DDLogicalThread *lt) override;
  
    void MutexInit(DDCallback *cb, DDMutex *m) override;
    void MutexBeforeLock(DDCallback *cb, DDMutex *m, bool wlock) override;
    void MutexAfterLock(DDCallback *cb, DDMutex *m, bool wlock,
                        bool trylock) override;
    void MutexBeforeUnlock(DDCallback *cb, DDMutex *m, bool wlock) override;
    void MutexDestroy(DDCallback *cb, DDMutex *m) override;
  
    DDReport *GetReport(DDCallback *cb) override;
  
    void MutexEnsureID(DDLogicalThread *lt, DDMutex *m);
    void ReportDeadlock(DDCallback *cb, DDMutex *m);
  };
  
  DDetector *DDetector::Create(const DDFlags *flags) {
    (void)flags;
    void *mem = MmapOrDie(sizeof(DD), "deadlock detector");
    return new(mem) DD(flags);
  }
  
  DD::DD(const DDFlags *flags)
      : flags(*flags) {
    dd.clear();
  }
  
  DDPhysicalThread* DD::CreatePhysicalThread() {
    return nullptr;
  }
  
  void DD::DestroyPhysicalThread(DDPhysicalThread *pt) {
  }
  
  DDLogicalThread* DD::CreateLogicalThread(u64 ctx) {
    DDLogicalThread *lt = (DDLogicalThread*)InternalAlloc(sizeof(*lt));
    lt->ctx = ctx;
    lt->dd.clear();
    lt->report_pending = false;
    return lt;
  }
  
  void DD::DestroyLogicalThread(DDLogicalThread *lt) {
    lt->~DDLogicalThread();
    InternalFree(lt);
  }
  
  void DD::MutexInit(DDCallback *cb, DDMutex *m) {
    m->id = 0;
    m->stk = cb->Unwind();
  }
  
  void DD::MutexEnsureID(DDLogicalThread *lt, DDMutex *m) {
    if (!dd.nodeBelongsToCurrentEpoch(m->id))
      m->id = dd.newNode(reinterpret_cast<uptr>(m));
    dd.ensureCurrentEpoch(&lt->dd);
  }
  
  void DD::MutexBeforeLock(DDCallback *cb,
      DDMutex *m, bool wlock) {
    DDLogicalThread *lt = cb->lt;
    if (lt->dd.empty()) return;  // This will be the first lock held by lt.
    if (dd.hasAllEdges(&lt->dd, m->id)) return;  // We already have all edges.
    SpinMutexLock lk(&mtx);
    MutexEnsureID(lt, m);
    if (dd.isHeld(&lt->dd, m->id))
      return;  // FIXME: allow this only for recursive locks.
    if (dd.onLockBefore(&lt->dd, m->id)) {
      // Actually add this edge now so that we have all the stack traces.
      dd.addEdges(&lt->dd, m->id, cb->Unwind(), cb->UniqueTid());
      ReportDeadlock(cb, m);
    }
  }
  
  void DD::ReportDeadlock(DDCallback *cb, DDMutex *m) {
    DDLogicalThread *lt = cb->lt;
    uptr path[20];
    uptr len = dd.findPathToLock(&lt->dd, m->id, path, ARRAY_SIZE(path));
    if (len == 0U) {
      // A cycle of 20+ locks? Well, that's a bit odd...
      Printf("WARNING: too long mutex cycle found\n");
      return;
    }
    CHECK_EQ(m->id, path[0]);
    lt->report_pending = true;
    len = Min<uptr>(len, DDReport::kMaxLoopSize);
    DDReport *rep = &lt->rep;
    rep->n = len;
    for (uptr i = 0; i < len; i++) {
      uptr from = path[i];
      uptr to = path[(i + 1) % len];
      DDMutex *m0 = (DDMutex*)dd.getData(from);
      DDMutex *m1 = (DDMutex*)dd.getData(to);
  
      u32 stk_from = -1U, stk_to = -1U;
      int unique_tid = 0;
      dd.findEdge(from, to, &stk_from, &stk_to, &unique_tid);
      // Printf("Edge: %zd=>%zd: %u/%u T%d\n", from, to, stk_from, stk_to,
      //    unique_tid);
      rep->loop[i].thr_ctx = unique_tid;
      rep->loop[i].mtx_ctx0 = m0->ctx;
      rep->loop[i].mtx_ctx1 = m1->ctx;
      rep->loop[i].stk[0] = stk_to;
      rep->loop[i].stk[1] = stk_from;
    }
  }
  
  void DD::MutexAfterLock(DDCallback *cb, DDMutex *m, bool wlock, bool trylock) {
    DDLogicalThread *lt = cb->lt;
    u32 stk = 0;
    if (flags.second_deadlock_stack)
      stk = cb->Unwind();
    // Printf("T%p MutexLock:   %zx stk %u\n", lt, m->id, stk);
    if (dd.onFirstLock(&lt->dd, m->id, stk))
      return;
    if (dd.onLockFast(&lt->dd, m->id, stk))
      return;
  
    SpinMutexLock lk(&mtx);
    MutexEnsureID(lt, m);
    if (wlock)  // Only a recursive rlock may be held.
      CHECK(!dd.isHeld(&lt->dd, m->id));
    if (!trylock)
      dd.addEdges(&lt->dd, m->id, stk ? stk : cb->Unwind(), cb->UniqueTid());
    dd.onLockAfter(&lt->dd, m->id, stk);
  }
  
  void DD::MutexBeforeUnlock(DDCallback *cb, DDMutex *m, bool wlock) {
    // Printf("T%p MutexUnLock: %zx\n", cb->lt, m->id);
    dd.onUnlock(&cb->lt->dd, m->id);
  }
  
  void DD::MutexDestroy(DDCallback *cb,
      DDMutex *m) {
    if (!m->id) return;
    SpinMutexLock lk(&mtx);
    if (dd.nodeBelongsToCurrentEpoch(m->id))
      dd.removeNode(m->id);
    m->id = 0;
  }
  
  DDReport *DD::GetReport(DDCallback *cb) {
    if (!cb->lt->report_pending)
      return nullptr;
    cb->lt->report_pending = false;
    return &cb->lt->rep;
  }
  
  } // namespace __sanitizer
  #endif // #if SANITIZER_DEADLOCK_DETECTOR_VERSION == 1
  