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digitalmars.D.learn - Garbage Collector profiling and the dynamic array reserve() function

reply Tony <tonytdominguez aol.com> writes:
Found this unanswered question on StackOverflow.

This program:

import std.stdio;

void add(ref int[] data)
{
     data ~= 1;
     data ~= 2;
}

void main()
{
     int[] a;
     writeln("capacity:",a.capacity);
     auto cap = a.reserve(1000); // allocated may be more than 
requested
     assert(cap >= 1000);
     assert(cap == a.capacity);
     writeln("capacity:",a.capacity);
     a.add();
     writeln(a);

}

compiled with "dmd -profile=gc"

has this output in profilegc.log

bytes allocated, allocations, type, function, file:line
               4	              1	int[] profiling.add profiling.d:8
               4	              1	int[] profiling.add profiling.d:7

The question is: why doesn't using reserve() cause an allocation 
to be shown?
Oct 16 2017
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 10/17/17 2:14 AM, Tony wrote:

 Found this unanswered question on StackOverflow.
 
 This program:
 
 import std.stdio;
 
 void add(ref int[] data)
 {
      data ~= 1;
      data ~= 2;
 }
 
 void main()
 {
      int[] a;
      writeln("capacity:",a.capacity);
      auto cap = a.reserve(1000); // allocated may be more than requested
      assert(cap >= 1000);
      assert(cap == a.capacity);
      writeln("capacity:",a.capacity);
      a.add();
      writeln(a);
 
 }
 
 compiled with "dmd -profile=gc"
 
 has this output in profilegc.log
 
 bytes allocated, allocations, type, function, file:line
                4                  1    int[]
profiling.add profiling.d:8
                4                  1    int[]
profiling.add profiling.d:7
 
 The question is: why doesn't using reserve() cause an allocation to be 
 shown?


I don't know what "allocations" represents, but reserve actually calls 
gc_malloc, and the others do not (the space is available to expand into 
the block). There should be only one allocation IMO.

-Steve
Oct 17 2017
parent reply Tony <tonytdominguez aol.com> writes:
On Tuesday, 17 October 2017 at 13:27:24 UTC, Steven Schveighoffer 
wrote:


 I don't know what "allocations" represents, but reserve 
 actually calls gc_malloc, and the others do not (the space is 
 available to expand into the block). There should be only one 
 allocation IMO.

 -Steve


So there should be a bug report written for this?
Oct 17 2017
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 10/18/17 1:40 AM, Tony wrote:

 On Tuesday, 17 October 2017 at 13:27:24 UTC, Steven Schveighoffer wrote:
 

 I don't know what "allocations" represents, but reserve actually calls 
 gc_malloc, and the others do not (the space is available to expand 
 into the block). There should be only one allocation IMO.


 
 So there should be a bug report written for this?
 


It all depends on what "allocations" means. I'd wait to find out from 
someone who is familiar with the GC profiling.

-Steve
Oct 18 2017
parent bauss <jj_1337 live.dk> writes:
On Wednesday, 18 October 2017 at 15:39:43 UTC, Steven 
Schveighoffer wrote:

 On 10/18/17 1:40 AM, Tony wrote:

 On Tuesday, 17 October 2017 at 13:27:24 UTC, Steven 
 Schveighoffer wrote:
 

 I don't know what "allocations" represents, but reserve 
 actually calls gc_malloc, and the others do not (the space is 
 available to expand into the block). There should be only one 
 allocation IMO.


 
 So there should be a bug report written for this?
 


 It all depends on what "allocations" means. I'd wait to find 
 out from someone who is familiar with the GC profiling.

 -Steve


I don't have a lot of clues on how the GC profiling work, but 
looking at reserve() it calls mem.xmalloc() for allocations which 
in fact calls GC.malloc().

Looking at the profiling for GC though:
https://github.com/dlang/dmd/blob/69567a32c5bffae5513b41e7691c91b50766b552/src/ddmd/e2ir.d#L5952

It doesn't look like there's anything for array reserve calls, 
unless:
  [ RTLSYM_ALLOCMEMORY, RTLSYM_TRACEALLOCMEMORY ]
are triggered from the allocations done in reserve(), but I have 
no idea about that.
Oct 22 2017