Question

True or False

28. “page fault” is resolved transparently by the kernel without notification to user 29. Virtual memory used in different processes cannot be mapped to the same physical memory 30. Dynamic memory can be allocated at compile time 31. free(NULL) is a valid statement which just silently returns 32. Using integers directly to represent signals should be avoided 33. After fork(), the child process will receive a copy of all signals set to its parent 34. After exec(), all signals are reset to their default actions for the child process 35. sigqueue() is different from kill() in that it can send a signal with payload data

Answer 1

28)T

Kernel incorporates regions table into the virtual address space abstraction implementation. Region table is implemented as a memory page which contains an array of thread ids of region managers.Regions table itself is mapped into the kernel part of the virtual address space which is located on a fixed address. As a result during page fault kernel can easily find the region table itself and identify the region manager responsible for the region to which fault address belongs, and to which kernel will send a page fault notification message. Each memory object is associated with a managing task, which is called a pager. This association enables the ability to handle page faults and page-out requests outside the kernel. Access to the pager is represented by a port to which the kernel can send messages to request data or to notify the pager about a change in the object’s primary memory cache.

29)F

It is a technique that is implemented using both hardware and software. It maps memory addresses used by a program, called virtual addresses, into physical addresses in computer memory.All memory references within a process are logical addresses that are dynamically translated into physical addresses at run time. This means that a process can be swapped in and out of main memory such that it occupies different places in main memory at different times during the course of execution.

30)F

C programming or any other programming language basically support two types of memory allocation.

1. Compile time memory allocation
2. Runtime memory allocation

Compile time memory allocation means reserving memory for variables, constants during the compilation process.Text also refer compile time memory allocation as static or stack memory allocation.

Memory allocated at runtime either through malloc(), calloc() or realloc() is called as runtime memory allocation.It refers runtime memory allocation as dynamic or heap memory allocation.

31)F

setting a pointer to NULL after free is supposed to prevent the dreaded "double free" problem when the same pointer value is passed to free more than once.

32)F

C does not have boolean data types, and normally uses integers for boolean testing.

Zero is used to represent false, and One is used to represent true.

33)T

using fork() system call, the address space of the Parent process is replicated. If the parent process calls wait() system call, then the execution of parent is suspended until the child is terminated.fork() creates a new process by duplicating the calling process, The new process, referred to as child, is an exact duplicate of the calling process, referred to as parent.fork starts a new process which is a copy of the one that calls it.Both parent and child processes are executed simultaneously.

34)F

The exec() family of functions replaces the current process image with a new process image. It loads the program into the current process space and runs it from the entry point.Control never returns to the original program unless there is an exec() error.

35)T

sigqueue() sends the signal specified in sig to the process whose PID is given in pid. The permissions required to send a signal are the same as for kill(2). As with kill(2), the null signal (0) can be used to check if a process with a given PID exists.The conditions under which a process has permission to queue a signal to another process with sigqueue() are the same as for the kill()function.