mfbt/tests/TestWeakPtr.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/WeakPtr.h"
   8
   9 using mozilla::SupportsWeakPtr;
  10 using mozilla::WeakPtr;
  11
  12 static char IamB[] = "B";
  13 static char IamC[] = "C";
  14 static char IamD[] = "D";
  15
  16 class B : public SupportsWeakPtr {
  17  public:
  18   char const* whoAmI() const { return IamB; }
  19 };
  20
  21 // To have a class C support weak pointers, inherit from SupportsWeakPtr.
  22 class C : public SupportsWeakPtr {
  23  public:
  24   int mNum;
  25
  26   C() : mNum(0) {}
  27
  28   ~C() {
  29     // Setting mNum in the destructor allows us to test against use-after-free
  30     // below
  31     mNum = 0xDEAD;
  32   }
  33
  34   char const* whoAmI() const { return IamC; }
  35
  36   void act() {}
  37
  38   bool isConst() { return false; }
  39
  40   bool isConst() const { return true; }
  41 };
  42
  43 // Derived from a class that supports weakptr, but doesn't implement itself
  44 // To check upcast works as expected
  45 class D : public B {
  46  public:
  47   char const* whoAmI() const { return IamD; }
  48 };
  49
  50 bool isConst(C*) { return false; }
  51
  52 bool isConst(const C*) { return true; }
  53
  54 int main() {
  55   C* c1 = new C;
  56   MOZ_RELEASE_ASSERT(c1->mNum == 0);
  57
  58   // Get weak pointers to c1. The first time,
  59   // a reference-counted WeakReference object is created that
  60   // can live beyond the lifetime of 'c1'. The WeakReference
  61   // object will be notified of 'c1's destruction.
  62   WeakPtr<C> w1 = c1;
  63   // Test a weak pointer for validity before using it.
  64   MOZ_RELEASE_ASSERT(w1);
  65   MOZ_RELEASE_ASSERT(w1 == c1);
  66   w1->mNum = 1;
  67   w1->act();
  68
  69   // Test taking another WeakPtr<C> to c1
  70   WeakPtr<C> w2 = c1;
  71   MOZ_RELEASE_ASSERT(w2);
  72   MOZ_RELEASE_ASSERT(w2 == c1);
  73   MOZ_RELEASE_ASSERT(w2 == w1);
  74   MOZ_RELEASE_ASSERT(w2->mNum == 1);
  75
  76   // Test a WeakPtr<const C>
  77   WeakPtr<const C> w3const = c1;
  78   MOZ_RELEASE_ASSERT(w3const);
  79   MOZ_RELEASE_ASSERT(w3const == c1);
  80   MOZ_RELEASE_ASSERT(w3const == w1);
  81   MOZ_RELEASE_ASSERT(w3const == w2);
  82   MOZ_RELEASE_ASSERT(w3const->mNum == 1);
  83
  84   // Test const-correctness of operator-> and operator T*
  85   MOZ_RELEASE_ASSERT(!w1->isConst());
  86   MOZ_RELEASE_ASSERT(w3const->isConst());
  87   MOZ_RELEASE_ASSERT(!isConst(w1));
  88   MOZ_RELEASE_ASSERT(isConst(w3const));
  89
  90   // Test that when a WeakPtr is destroyed, it does not destroy the object that
  91   // it points to, and it does not affect other WeakPtrs pointing to the same
  92   // object (e.g. it does not destroy the WeakReference object).
  93   {
  94     WeakPtr<C> w4local = c1;
  95     MOZ_RELEASE_ASSERT(w4local == c1);
  96   }
  97   // Now w4local has gone out of scope. If that had destroyed c1, then the
  98   // following would fail for sure (see C::~C()).
  99   MOZ_RELEASE_ASSERT(c1->mNum == 1);
 100   // Check that w4local going out of scope hasn't affected other WeakPtr's
 101   // pointing to c1
 102   MOZ_RELEASE_ASSERT(w1 == c1);
 103   MOZ_RELEASE_ASSERT(w2 == c1);
 104
 105   // Now construct another C object and test changing what object a WeakPtr
 106   // points to
 107   C* c2 = new C;
 108   c2->mNum = 2;
 109   MOZ_RELEASE_ASSERT(w2->mNum == 1);  // w2 was pointing to c1
 110   w2 = c2;
 111   MOZ_RELEASE_ASSERT(w2);
 112   MOZ_RELEASE_ASSERT(w2 == c2);
 113   MOZ_RELEASE_ASSERT(w2 != c1);
 114   MOZ_RELEASE_ASSERT(w2 != w1);
 115   MOZ_RELEASE_ASSERT(w2->mNum == 2);
 116
 117   // Destroying the underlying object clears weak pointers to it.
 118   // It should not affect pointers that are not currently pointing to it.
 119   delete c1;
 120   MOZ_RELEASE_ASSERT(!w1, "Deleting an object should clear WeakPtr's to it.");
 121   MOZ_RELEASE_ASSERT(!w3const,
 122                      "Deleting an object should clear WeakPtr's to it.");
 123   MOZ_RELEASE_ASSERT(w2,
 124                      "Deleting an object should not clear WeakPtr that are not "
 125                      "pointing to it.");
 126
 127   delete c2;
 128   MOZ_RELEASE_ASSERT(!w2, "Deleting an object should clear WeakPtr's to it.");
 129
 130   // Check that we correctly upcast to the base class supporting weakptr
 131   D* d = new D;
 132   WeakPtr<B> db = d;
 133
 134   // You should be able to use WeakPtr<D> even if it's a base class which
 135   // implements SupportsWeakPtr.
 136   WeakPtr<D> weakd = d;
 137
 138   MOZ_RELEASE_ASSERT(db->whoAmI() == IamB);
 139   MOZ_RELEASE_ASSERT(weakd.get() == db.get());
 140
 141   delete d;
 142
 143   MOZ_RELEASE_ASSERT(!db);
 144   MOZ_RELEASE_ASSERT(!weakd);
 145 }