Process and Address Space

Address space is the kernel abstraction of managing the memory
pages allocation for the process. Process needs memory address
space to store text instruction, data segment,heap as tmp process
space and stack

HW context: platform specific process execution environment
such as registers ------ CPU
address space ------------Memory

SW context: process credentials, open file lists, PIDs, signal disposition, signal handler, scheduling class and priority, process state,

Most of the process has stdin, stdout, stderr which define the source and destination
of input and output char streams for the process.

Solaris kernel, a process is composed of LWP and kthread. It is a kernel data strcution
linked to the process structure. This threading model seperate the user land threads with
kernel threads.

User land thread is created by routine call: thr_create(3T) or pthread_create(3T) from
libthread.so and libpthread.so. User thread has it's own scheduling and priority scheme
which different from kernel scheduling class and priority. It is done by calling into
thread library dispatcher and switch routines periodically at predefined preemption points.
User land thread is scheduled by linking on to a available LWP. It is required for a user
land thread to be executed. However, user thread is created does not mean LWP is created.
It must be specified as user thread to have kernel to create LWP from THR_NEW_LWP or THR_BOUND
flag. But for a threaded process with many bound LWPs with kernel thread will cause performance
impact.

In addition, thr_setconcurrency(3T) informs kernel that how may threads programmer wishes to run.
Without specification from code, thread library will maintain the reasonable number of LWPs for user land thread execution.

System should balance the case which there are too many LWPs or no enough LWPs to run.
Too many LWP cause kernel overhead to manage and too less LWPs cause many runnable user
land threads wait for resources for execution.

As traditional process modlel, exec or fork create new process.

In a multi thread process model, all HW context are not shared among user land threads
However, SW context such as address space, PIDs, credentials, signal hanlders etc. are shared.