What is thread Safe in java

Question

Possible Duplicate    What does threadsafe mean        I am very confused that any class is Thread safe  I am understanding that  if any class is thread safe then it has some specific on its methods as synchronized   Is it right or wrong  Please help me by elaborating on the meaning of it

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Thread safe simply means that it may be used from multiple threads at the same time without causing problems  This can mean that access to any resources are synchronized  or whatever

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As Seth stated thread safe means that a method or class instance can be used by multiple threads at the same time without any problems occuring   Consider the following method   private int myInt   0  public int AddOne         int tmp   myInt      tmp   tmp   1      myInt   tmp      return tmp      Now thread A and thread B both would like to execute AddOne     but A starts first and reads the value of myInt  0  into tmp  Now for some reason the scheduler decides to halt thread A and defer execution to thread B  Thread B now also reads the value of myInt  still 0  into it s own variable tmp  Thread B finishes the entire method  so in the end myInt   1  And 1 is returned  Now it s Thread A s turn again  Thread A continues  And adds 1 to tmp  tmp was 0 for thread A    And then saves this value in myInt  myInt is again 1   So in this case the method AddOne   was called two times  but because the method was not implemented in a thread safe way the value of myInt is not 2  as expected  but 1 because the second thread read the variable myInt before the first thread finished updating it   Creating thread safe methods is very hard in non trivial cases  And there are quite a few techniques  In Java you can mark a method as synchronized  this means that only one thread can execute that method at a given time  The other threads wait in line  This makes a method thread safe  but if there is a lot of work to be done in a method  then this wastes a lot of time  Another technique is to  mark only a small part of a method as synchronized  by creating a lock or semaphore  and locking this small part  usually called the critical section   There are even some methods that are implemented as lockless thread safe  which means that they are built in such a way that multiple threads can race through them at the same time without ever causing problems  this can be the case when a method only executes one atomic call  Atomic calls are calls that can t be interrupted and can only be done by one thread at a time

[java] What is thread Safe in java?

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Examples related to thread-safety