www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - In what situation can new Struct() return null?

reply faissaloo <faissaloo gmail.com> writes:
My program contains the following statement:
     auto newChildNode = new Node();

In debugging I have found that this pointer evaluates to null, 
what could cause this? I should have plenty of memory, my only 
other idea is some sort of heap corruption.
May 10 2019
parent reply Cym13 <cpicard purrfect.fr> writes:
On Friday, 10 May 2019 at 10:11:51 UTC, faissaloo wrote:

 My program contains the following statement:
     auto newChildNode = new Node();

 In debugging I have found that this pointer evaluates to null, 
 what could cause this? I should have plenty of memory, my only 
 other idea is some sort of heap corruption.


Could you share a complete, concise, compilable example 
demonstrating that bug? One line is rather short to understand 
what's happening.
May 10 2019
parent reply faissaloo <faissaloo gmail.com> writes:
On Friday, 10 May 2019 at 12:19:29 UTC, Cym13 wrote:

 On Friday, 10 May 2019 at 10:11:51 UTC, faissaloo wrote:

 My program contains the following statement:
     auto newChildNode = new Node();

 In debugging I have found that this pointer evaluates to null, 
 what could cause this? I should have plenty of memory, my only 
 other idea is some sort of heap corruption.


 Could you share a complete, concise, compilable example 
 demonstrating that bug? One line is rather short to understand 
 what's happening.


Unfortunately not, I can't seem to reproduce it outside my 
codebase.
May 10 2019
next sibling parent reply "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Fri, May 10, 2019 at 05:32:25PM +0000, faissaloo via Digitalmars-d-learn
wrote:

 On Friday, 10 May 2019 at 12:19:29 UTC, Cym13 wrote:

 On Friday, 10 May 2019 at 10:11:51 UTC, faissaloo wrote:

 My program contains the following statement:
     auto newChildNode = new Node();
 
 In debugging I have found that this pointer evaluates to null,
 what could cause this? I should have plenty of memory, my only
 other idea is some sort of heap corruption.


 
 Could you share a complete, concise, compilable example
 demonstrating that bug? One line is rather short to understand
 what's happening.


 
 Unfortunately not, I can't seem to reproduce it outside my codebase.


Perhaps try Dustmite on it?

AFAIK, calling new on a struct should never return null. So there must
be something else not quite right here.  But without actual code it's
anybody's guess as to what it might be.

The last time I heard somebody run into this, it was caused by some
unrelated compiler codegen bug that left the CPU registers in an
inconsistent state, thus causing an unrelated call to `new` to return
the wrong value.  Perhaps you could try a different compiler to see if
that makes a difference?


T

-- 
The fact that anyone still uses AOL shows that even the presence of options
doesn't stop some people from picking the pessimal one. - Mike Ellis
May 10 2019
parent faissaloo <faissaloo gmail.com> writes:
On Friday, 10 May 2019 at 17:54:44 UTC, H. S. Teoh wrote:

 Perhaps try Dustmite on it?

 AFAIK, calling new on a struct should never return null. So 
 there must be something else not quite right here.  But without 
 actual code it's anybody's guess as to what it might be.

 The last time I heard somebody run into this, it was caused by 
 some unrelated compiler codegen bug that left the CPU registers 
 in an inconsistent state, thus causing an unrelated call to 
 `new` to return the wrong value.  Perhaps you could try a 
 different compiler to see if that makes a difference?


 T


I've tried a number of different compilers and the issue 
persists, I think the issue is the garbage collector. This issue 
did have spontaneously disappear but generally with my project 
there seem to be a number of memory corruption issues that as far 
as I can tell, shouldn't be happening. I've submitted a bug 
report here: https://issues.dlang.org/show_bug.cgi?id=19860
May 11 2019
prev sibling parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Friday, May 10, 2019 11:54:44 AM MDT H. S. Teoh via Digitalmars-d-learn 
wrote:

 On Fri, May 10, 2019 at 05:32:25PM +0000, faissaloo via Digitalmars-d-


learn wrote:

 On Friday, 10 May 2019 at 12:19:29 UTC, Cym13 wrote:

 On Friday, 10 May 2019 at 10:11:51 UTC, faissaloo wrote:

 My program contains the following statement:
     auto newChildNode = new Node();

 In debugging I have found that this pointer evaluates to null,
 what could cause this? I should have plenty of memory, my only
 other idea is some sort of heap corruption.


 Could you share a complete, concise, compilable example
 demonstrating that bug? One line is rather short to understand
 what's happening.


 Unfortunately not, I can't seem to reproduce it outside my codebase.


 Perhaps try Dustmite on it?

 AFAIK, calling new on a struct should never return null. So there must
 be something else not quite right here.  But without actual code it's
 anybody's guess as to what it might be.


If the GC fails to allocate, it will throw an OutOfMemoryError. So, new
should never return null. I have no clue what could be happening in this
case.

- Jonathan M Davis
May 11 2019