gecko-dev/mfbt/tests/TestWeakPtr.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/WeakPtr.h"

using mozilla::SupportsWeakPtr;
using mozilla::WeakPtr;

static char IamB[] = "B";
static char IamC[] = "C";
static char IamD[] = "D";

class B : public SupportsWeakPtr {
 public:
  char const* whoAmI() const { return IamB; }
};

// To have a class C support weak pointers, inherit from SupportsWeakPtr.
class C : public SupportsWeakPtr {
 public:
  int mNum;

  C() : mNum(0) {}

  ~C() {
    // Setting mNum in the destructor allows us to test against use-after-free
    // below
    mNum = 0xDEAD;
  }

  char const* whoAmI() const { return IamC; }

  void act() {}

  bool isConst() { return false; }

  bool isConst() const { return true; }
};

// Derived from a class that supports weakptr, but doesn't implement itself
// To check upcast works as expected
class D : public B {
 public:
  char const* whoAmI() const { return IamD; }
};

bool isConst(C*) { return false; }

bool isConst(const C*) { return true; }

int main() {
  C* c1 = new C;
  MOZ_RELEASE_ASSERT(c1->mNum == 0);

  // Get weak pointers to c1. The first time,
  // a reference-counted WeakReference object is created that
  // can live beyond the lifetime of 'c1'. The WeakReference
  // object will be notified of 'c1's destruction.
  WeakPtr<C> w1 = c1;
  // Test a weak pointer for validity before using it.
  MOZ_RELEASE_ASSERT(w1);
  MOZ_RELEASE_ASSERT(w1 == c1);
  w1->mNum = 1;
  w1->act();

  // Test taking another WeakPtr<C> to c1
  WeakPtr<C> w2 = c1;
  MOZ_RELEASE_ASSERT(w2);
  MOZ_RELEASE_ASSERT(w2 == c1);
  MOZ_RELEASE_ASSERT(w2 == w1);
  MOZ_RELEASE_ASSERT(w2->mNum == 1);

  // Test a WeakPtr<const C>
  WeakPtr<const C> w3const = c1;
  MOZ_RELEASE_ASSERT(w3const);
  MOZ_RELEASE_ASSERT(w3const == c1);
  MOZ_RELEASE_ASSERT(w3const == w1);
  MOZ_RELEASE_ASSERT(w3const == w2);
  MOZ_RELEASE_ASSERT(w3const->mNum == 1);

  // Test const-correctness of operator-> and operator T*
  MOZ_RELEASE_ASSERT(!w1->isConst());
  MOZ_RELEASE_ASSERT(w3const->isConst());
  MOZ_RELEASE_ASSERT(!isConst(w1));
  MOZ_RELEASE_ASSERT(isConst(w3const));

  // Test that when a WeakPtr is destroyed, it does not destroy the object that
  // it points to, and it does not affect other WeakPtrs pointing to the same
  // object (e.g. it does not destroy the WeakReference object).
  {
    WeakPtr<C> w4local = c1;
    MOZ_RELEASE_ASSERT(w4local == c1);
  }
  // Now w4local has gone out of scope. If that had destroyed c1, then the
  // following would fail for sure (see C::~C()).
  MOZ_RELEASE_ASSERT(c1->mNum == 1);
  // Check that w4local going out of scope hasn't affected other WeakPtr's
  // pointing to c1
  MOZ_RELEASE_ASSERT(w1 == c1);
  MOZ_RELEASE_ASSERT(w2 == c1);

  // Now construct another C object and test changing what object a WeakPtr
  // points to
  C* c2 = new C;
  c2->mNum = 2;
  MOZ_RELEASE_ASSERT(w2->mNum == 1);  // w2 was pointing to c1
  w2 = c2;
  MOZ_RELEASE_ASSERT(w2);
  MOZ_RELEASE_ASSERT(w2 == c2);
  MOZ_RELEASE_ASSERT(w2 != c1);
  MOZ_RELEASE_ASSERT(w2 != w1);
  MOZ_RELEASE_ASSERT(w2->mNum == 2);

  // Destroying the underlying object clears weak pointers to it.
  // It should not affect pointers that are not currently pointing to it.
  delete c1;
  MOZ_RELEASE_ASSERT(!w1, "Deleting an object should clear WeakPtr's to it.");
  MOZ_RELEASE_ASSERT(!w3const,
                     "Deleting an object should clear WeakPtr's to it.");
  MOZ_RELEASE_ASSERT(w2,
                     "Deleting an object should not clear WeakPtr that are not "
                     "pointing to it.");

  delete c2;
  MOZ_RELEASE_ASSERT(!w2, "Deleting an object should clear WeakPtr's to it.");

  // Check that we correctly upcast to the base class supporting weakptr
  D* d = new D;
  WeakPtr<B> db = d;

  // You should be able to use WeakPtr<D> even if it's a base class which
  // implements SupportsWeakPtr.
  WeakPtr<D> weakd = d;

  MOZ_RELEASE_ASSERT(db->whoAmI() == IamB);
  MOZ_RELEASE_ASSERT(weakd.get() == db.get());

  delete d;

  MOZ_RELEASE_ASSERT(!db);
  MOZ_RELEASE_ASSERT(!weakd);
}