[swift-corelibs-dev] Memory leak with String.range(options: .regularExpression) [SR-3536]

[Tony Parker]

Hi Nethra,

> On Feb 7, 2017, at 11:44 PM, Nethra Ravindran via swift-corelibs-dev <swift-corelibs-dev at swift.org> wrote:
> 
> 
> 
> 
> Hi everyone,
> 
> I am working on https://bugs.swift.org/browse/SR-3536 <https://bugs.swift.org/browse/SR-3536>
> There is a memory leak when searching for the substring of a string using regular expression.
> 
> 
> import Foundation
> 
> let myString = "Foo"
> for _ in 1...10000 {
>   let _ = myString.range(of: "bar", options: .regularExpression)
> }
> 
> 
> From the above test case i could see that over a period of time, around 60 Mb of memory was leaked. 
> 
> I see in String.range we eventually call NSString._createRegexForPattern. Here we maintain a mapping between NSString and NSRegularExpression object in NSCache<NSString, NSRegularExpression>. All the entries in the cache are maintained in a dictionary ( _entries ) which takes the UnsafeRawPointer as the key, which seems to be the address of the NSString Object and NSCachedEntry as value.
> 
> Though the pattern is of type String, it is stored in the NSCache as NSString. And since we are storing the NSCachedEntry objects in a dictionary indexed by the address (UnsafeRawPointer) of the NSString object, there is a new cache entry created for each iteration ( in the test case ) though the pattern string remains the same.
> 
> Can someone guide me about how to go about resolving this issue.
> 
> 

Looks like you’ve done most of the analysis, so you’re already pretty much there. =)

Is there some other way we could be caching the results here?

- Tony
> Thank you.
> 
> - Nethra Ravindran
> 
> 
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