| Memory leak in STRMID [message #92105] |
Wed, 14 October 2015 04:26  |
Heinz Stege
Messages: 189
Registered: January 2003
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Senior Member |
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Hi all,
I believe that there is a bug within IDL's strmid function. However
I'm using a 5 years old version of IDL. So this bug may be fixed in
the meantime.
There seems to be a memory leak in the strmid funcion. When you
calculate a substring c of a very long string b
c=strmid(b,1000,10)
then the short string c (10 chars in this case) needs as much memory
as the long string b.
Here is the demo (and a workaround):
First I start a fresh IDL session an look for the memory consumption:
|IDL> help,/mem
|heap memory used: 797011, max: 800529, gets: 1137, frees: 291
About 1 MB overhead. Seems to be okay for running the workbench. Then
I create a huge string with 10 million chars:
|IDL> b=byte((randomu(seed,10000000,/long) mod 255)+1)
|IDL> help,/mem
|heap memory used: 10797258, max: 50797356, gets: 1152, frees: 304
|IDL> b=string(b)
|IDL> help,/mem
|heap memory used: 10797072, max: 20797211, gets: 1164, frees: 316
The string needs 10 MB memory. So far so good. Now I create a
substring with strmid:
|IDL> c=strmid(b,1000,10)
|IDL> help,/mem
|heap memory used: 20796961, max: 20797050, gets: 1176, frees: 327
Oops, the result string with 10 chars needs 10 MB too? Is it really 10
chars long?
|IDL> help,strlen(b)
|<Expression> LONG = 10000000
|IDL> help,strlen(c)
|<Expression> LONG = 10
|IDL> help,/mem
|heap memory used: 20796822, max: 20797026, gets: 1197, frees: 348
Yes it is. 10 MB for 10 chars! Can we make a copy of c, and how much
memory will it need?
|IDL> cc=c
|IDL> help,/mem
|heap memory used: 20796753, max: 20796833, gets: 1209, frees: 359
The copy of c needs only a few byts. That's fine. How can we release
the unjustified memory usage of c? Does a simple operation help?
|IDL> c+=''
|IDL> help,/mem
|heap memory used: 10796631, max: 20796759, gets: 1221, frees: 371
Aah, it helps. This is a workaround.
|IDL> print,!version
|{ x86 Win32 Windows Microsoft Windows 8.0.1 Oct 5 2010 32 64}
And now it's up to someone of you, to check verion 8.5. Unfortunately
I don't have this version.
Cheers, Heinz
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