Crash when compare 2 String many of times

Question

Created Sep ’21

Replies 5

Boosts 0

Views 1.3k

Participants 4

I have a array of contacts (about 1 millions elements), i must compare many of times the id of a contact to find out contact i need (the list was order by id so i'm using binary search). It did crash, this is my code and backtrace:

struct Contact {
  let blIdContact: String
  let timeStamp: Int64
}
func binarySearch(in contacts: [Contact], for value: String) -> Int? {
  var left = 0
  var right = contacts.count - 1
  while left <= right {
    let middle = Int(floor(Double(left + right) / 2.0))
    if contacts[middle].blIdContact < value {
      left = middle + 1
    } else if contacts[middle].blIdContact > value {
      right = middle - 1
    } else {
      return middle
    }
  }
  return nil
}

This is backtrace at crashed thread:

Thread 25 Crashed:
0   libobjc.A.dylib               	0x00000001b38771c8 objc_msgSend + 8
1   libswiftCore.dylib            	0x00000001a2b1a464 _foreignNormalize(readIndex:endIndex:guts:outputBuffer:icuInputBuffer:icuOutputBuffer:) + 236 (StringBridge.swift:159)
2   libswiftCore.dylib            	0x00000001a2b231cc _StringGutsSlice._slowCompare(with:expecting:) + 3464 (StringComparison.swift:375)
3   libswiftCore.dylib            	0x00000001a2b2115c _stringCompareInternal(_:_:expecting:) + 308 (StringComparison.swift:185)
4   Bluezone                      	0x00000001023f1450 binarySearch(in:for:) + 37968 (Utils.swift:46)

This is full backtrace:

2021-07-30_22-25-18.6439_+0700-35c69dd5f3150833c617797438762310e264d319.crash

Answered by DTS Engineer in 688191022

Crash when compare 2 String many of times

See my response on your other thread.

Share and Enjoy
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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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Answer 1

Claude31 OP

Sep ’21

When does it crash (could you print left and right at each step ?

Are you sure contacts are fully ordered by id ? Are blIdContact all strings from Int ?

There is something I don't understand in your code:

how could left be greater than right ?
Are you sure your id are such that < comparison works in this case ("300" is not less than "1000" because of string comparison).

1

Answer 2

vudat081299 OP

Sep ’21

Have one thing i didn't mention above, in thread 25 note about index of line crashed (Utils.swift:46) it's:

if contacts[middle].blIdContact < value {

0

Answer 3

DTS Engineer OP

Apple

Sep ’21

Accepted Answer

Crash when compare 2 String many of times

See my response on your other thread.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0

Answer 4

Claude31 OP

Sep ’21

I do not see the index error in crash log:

Thread 25 Crashed:
0   libobjc.A.dylib               	0x00000001b38771c8 objc_msgSend + 8
1   libswiftCore.dylib            	0x00000001a2b1a464 _foreignNormalize(readIndex:endIndex:guts:outputBuffer:icuInputBuffer:icuOutputBuffer:) + 236 (StringBridge.swift:159)
2   libswiftCore.dylib            	0x00000001a2b231cc _StringGutsSlice._slowCompare(with:expecting:) + 3464 (StringComparison.swift:375)
3   libswiftCore.dylib            	0x00000001a2b2115c _stringCompareInternal(_:_:expecting:) + 308 (StringComparison.swift:185)
4   Bluezone                      	0x00000001023f1450 binarySearch(in:for:) + 37968 (Utils.swift:46)
5   Bluezone                      	0x00000001024028c4 specialized static BluezoneIdTrace.checkContactF(bluezoneDailyKeyk:timeDk:max:timeTe:) + 108740 (BluezoneIdTrace.swift:307)
6   Bluezone                      	0x0000000102401928 static BluezoneIdTrace.isContactF(dataF0:) + 104744 (BluezoneIdTrace.swift:255)
7   Bluezone                      	0x0000000102412158 partial apply for closure #1 in ScannerManager.checkContactF(_:resolve:rejecter:) + 172376 (<compiler-generated>:0)
8   Bluezone                      	0x000000010240d6f4 thunk for @escaping @callee_guaranteed () -> () + 153332 (<compiler-generated>:0)
9   libdispatch.dylib             	0x000000019e9c1a84 _dispatch_call_block_and_release + 32 (init.c:1466)
10  libdispatch.dylib             	0x000000019e9c381c _dispatch_client_callout + 20 (object.m:559)
11  libdispatch.dylib             	0x000000019e9cb004 _dispatch_lane_serial_drain + 620 (inline_internal.h:2557)
12  libdispatch.dylib             	0x000000019e9cbc00 _dispatch_lane_invoke + 404 (queue.c:3862)
13  libdispatch.dylib             	0x000000019e9d64bc _dispatch_workloop_worker_thread + 764 (queue.c:6589)
14  libsystem_pthread.dylib       	0x00000001ea93a7a4 _pthread_wqthread + 276
15  libsystem_pthread.dylib       	0x00000001ea94174c start_wqthread + 8

How do you load the 1M+ contacts ? Are you sure it is fully loaded when you call binarySearch ?

So, add some print statements:

    let middle = Int(floor(Double(left + right) / 2.0))
    print("middle", middle)
    print("contact", contacts[middle])
    print("contact Id",  contacts[middle].blIdContact)
    print("value", value)
    if contacts[middle].blIdContact < value {

What do you get just before crash ?

0

Answer 5

OOPer OP

Sep ’21

I tried your code a few tens of times with 100 millions elements in contacts. It never crashed. So the number of String comparison does not matter. I guess it is a problem of multithreading, as it may be revealed only when huge number of elements involved. Anyway, you should better concentrate on the first thread of yours and respond to eskimo.

0