May be my question is stupid. But i would like to get it cleared. We know that functions are loaded in memory only once and when you create new objects, only instance variables gets created, functions are never created. My question is, say suppose there is server and all clients access a method named createCustomer(). Say suppose all clients do something which fired createCustomer on server. So, if the method is in middle of execution and new client fires it. Will the new request be put on wait? or new request also will start executing the method? How does it all get managed when there is only one copy of function in memory? No book mentions answers to this type of questions. So i am posting here where i am bound to get answers :).
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Functions are code which is then executed in a memory context. The code can be run many times in parallel (literally in parallel on a multi-processor machine), but each of those calls will execute in a different memory context (from the point of view of local variables and such). At a low level this works because the functions will reference local variables as offsets into memory on something called a “stack” which is pointed to by a processor register called the “stack pointer” (or in some interpreted languages, an analog of that register at a higher level), and the value of this register will be different for different calls to the function. So the
xlocal variable in one call to functionfoois in a different location in memory than thexlocal variable in another call tofoo, regardless of whether those calls happen simultaneously.Instance variables are different, they’re referenced via a reference (pointer) to the memory allocated to the instance of an object. Two running copies of the same function might access the same instance variable at exactly the same time; similarly, two different functions might do so. This is why we get into “threading” or concurrency issues, synchronization, locks, race conditions, etc. But it’s also one reason things can be highly efficient.