On 8 Feb 2017, at 16:51, Tony Parker via swift-corelibs-dev
<swift-corelibs-dev@swift.org> wrote:
>
> Hi Nethra,
>
>> On Feb 7, 2017, at 11:44 PM, Nethra Ravindran via swift-corelibs-dev
>> <swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@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?
There's a 'cache.countLimit = 10' set on the cache:
https://github.com/apple/swift-corelibs-foundation/blob/16657160c2c441a58ea01bf7baa90607a0b395f7/Foundation/NSString.swift#L109
<https://github.com/apple/swift-corelibs-foundation/blob/16657160c2c441a58ea01bf7baa90607a0b395f7/Foundation/NSString.swift#L109>
Shouldn't it start discarding some of the previous entries after it hits the
first 10?
Alex
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