GC.inFinalizer

// Only code called from a destructor is executed during finalization.
assert(!GC.inFinalizer);

1 enum Outcome
2 {
3     notCalled,
4     calledManually,
5     calledFromDruntime
6 }
7 
8 static class Resource
9 {
10     static Outcome outcome;
11 
12     this()
13     {
14         outcome = Outcome.notCalled;
15     }
16 
17     ~this()
18     {
19         if (GC.inFinalizer)
20         {
21             outcome = Outcome.calledFromDruntime;
22 
23             import core.exception : InvalidMemoryOperationError;
24             try
25             {
26                 /*
27                  * Presently, allocating GC memory during finalization
28                  * is forbidden and leads to
29                  * `InvalidMemoryOperationError` being thrown.
30                  *
31                  * `GC.inFinalizer` can be used to guard against
32                  * programming erros such as these and is also a more
33                  * efficient way to verify whether a destructor was
34                  * invoked by the GC.
35                  */
36                 cast(void) GC.malloc(1);
37                 assert(false);
38             }
39             catch (InvalidMemoryOperationError e)
40             {
41                 return;
42             }
43             assert(false);
44         }
45         else
46             outcome = Outcome.calledManually;
47     }
48 }
49 
50 static void createGarbage()
51 {
52     auto r = new Resource;
53     r = null;
54 }
55 
56 assert(Resource.outcome == Outcome.notCalled);
57 createGarbage();
58 GC.collect;
59 assert(
60     Resource.outcome == Outcome.notCalled ||
61     Resource.outcome == Outcome.calledFromDruntime);
62 
63 auto r = new Resource;
64 GC.runFinalizers((cast(const void*)typeid(Resource).destructor)[0..1]);
65 assert(Resource.outcome == Outcome.calledFromDruntime);
66 Resource.outcome = Outcome.notCalled;
67 
68 debug(MEMSTOMP) {} else
69 {
70     // assume Resource data is still available
71     r.destroy;
72     assert(Resource.outcome == Outcome.notCalled);
73 }
74 
75 r = new Resource;
76 assert(Resource.outcome == Outcome.notCalled);
77 r.destroy;
78 assert(Resource.outcome == Outcome.calledManually);