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How to guarantee no deadlock

I am stuck in one question in an interview.

Given two threads, and each of them has a lock, how to guarantee the absence of deadlock.

I know that it's not easy to avoid a dead end, so I'm stuck. Can someone give a hint.

Thank!

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7 answers

The description is a bit missing, but if you put the blocking order in place (for example, if A and B are locked, never block B, if you already locked A, and you never let go of A, and B is locked), then the deadlock won Not happen.

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, , . , Banker Algorithm.

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:

A 1, 2

B 2 1

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- , , WaitForMultipleObjects(). API Windows, ( ) .

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/ . , , , - . , concurrency.

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  • :
    , . :
    i) Thread A Lock LEFT
    ii) B RIGHT
    iii) A Lock RIGHT
    iv) B Lock LEFT
    --- >

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    void transferFund( Account A, Account B, Amount x)
{
    synchronized(A)
    { 
        synchronized(B)
        {
          // do transfer update balance
        }
    }
}

    : 1 - transferFund (A1, B1, 10); Thread 2 - transferFund (B1, A1, 20);

    : , , , . -

    if( A1.hashCode()  < B1.hashCode())
  { Lock A1 then Lock B1 }
else
  { Lock B1 then Lock A1 }

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