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Fix issue 16046 - ScopedAllocator does not set prev, causing segfaults #4742

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merged 1 commit into from Aug 24, 2016
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Fix issue 16046 - ScopedAllocator does not set prev, causing segfaults #4742

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15 changes: 15 additions & 0 deletions std/experimental/allocator/building_blocks/scoped_allocator.d
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Expand Up @@ -89,6 +89,8 @@ struct ScopedAllocator(ParentAllocator)
toInsert.prev = null;
toInsert.next = root;
toInsert.length = n;
assert(!root || !root.prev);
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Quite recently there was a longer discussion on a PR about the ~200 HALTs in Phobos that come without message, but segfault. Maybe we could tell the user at least what has gone wrong?
e.g. "Invalid allocation. Root node isn't at the top of the stack"

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On top of the doubly-linked list actually ;-)
As we are at this, I'd suggest to add "Please, file an issue" or something like that, because if the assertion triggers, it's not a precondition gone wrong from the user, but rather an implementation bug.

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This will be a regular assert, not a HALT, because it's not compile-time zero.

if (root) root.prev = toInsert;
root = toInsert;
return b;
}
Expand Down Expand Up @@ -128,6 +130,7 @@ struct ScopedAllocator(ParentAllocator)
n.prev = null;
n.next = root;
n.length = s;
if (root) root.prev = n;
root = n;
}
return result;
Expand Down Expand Up @@ -204,3 +207,15 @@ unittest
import std.experimental.allocator.gc_allocator : GCAllocator;
testAllocator!(() => ScopedAllocator!GCAllocator());
}

unittest // https://issues.dlang.org/show_bug.cgi?id=16046
{
import std.exception;
import std.experimental.allocator;
import std.experimental.allocator.mallocator;
ScopedAllocator!Mallocator alloc;
auto foo = alloc.make!int(1).enforce;
auto bar = alloc.make!int(2).enforce;
alloc.dispose(foo);
alloc.dispose(bar); // segfault here
}
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@wilzbach wilzbach Aug 23, 2016 •
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Maybe we can add another test and deallocate in non-list order?
e.g.

alloc.dispose(el2);
alloc.dispose(el3);
alloc.dispose(el1);
alloc.dispose(el4);