Chapter 6 Implementing Processes, Threads, and Resources

Implementing the Process Abstraction Pi Address Space Pi CPU Pi Executable Memory Pj Address Space Pj CPU Pj Executable Memory Pk Address Space … Pk CPU Pk Executable Memory OS interface OS Address Space CPU ALU Machine Executable Memory Control Unit …

External View of the Process Manager Application Program Device Mgr Process Mgr Memory Mgr File Mgr Windows CreateThread() CreateProcess() CloseHandle() WaitForSingleObject() fork() wait() exec() Device Mgr Process Mgr Memory Mgr File Mgr UNIX Hardware

Process Manager Responsibilities Define & implement the essential characteristics of a process and thread Algorithms to define the behavior Data structures to preserve the state of the execution Define what “things” threads in the process can reference – the address space (most of the “things” are memory locations) Manage the resources used by the processes/threads Tools to create/destroy/manipulate processes & threads Tools to time-multiplex the CPU – Scheduling the (Chapter 7) Tools to allow threads to synchronization the operation with one another (Chapters 8-9) Mechanisms to handle deadlock (Chapter 10) Mechanisms to handle protection (Chapter 14)

Modern Processes and Threads Thrdj in Pi Thrdk in Pi … Pi CPU … … OS interface …

Processes &Threads State Stack State Stack Map Address Space Map Program Static data Resources

Process Address Space Process address space is the collection of addresses that a thread can reference. Normally, it refers to an executable memory location. However, due to the nature of a process, a process address space can also be associated with other machine abstract elements-such as, files, device registers and other objects.

Memory-Mapped-Resources 1. Most of the components in a computer system can be referenced by memory addresses. (One of the exception is the processor it self) 2. The address space provides a uniform mechanism by which a process can reference bytes in all memory-mapped resources. 3. Each resource manager is responsible for binding addresses with addressable elements of the resource.

The Address Space Process Executable Memory Address Space Address Binding Process Files Other objects

Building the Address Space Some parts are built into the environment Files System services Some parts are imported at runtime Mailboxes Network connections Memory addresses are created at compile (and run) time

Tracing the Hardware Process Machine is Powered up Bootstap Process Manager Interrupt Handler P1 P,2 Pn Loader Load the kernel Initialization Execute a thread … Schedule Hardware process progress Service an interrupt

Responsibilities of Process Manager 1. Process Creation and Termination 2. Thread Creation and Termination 3. Process/Thread Synchronization 4. Resource Allocation 5. Resource Protection 6. Co-operate with Device Manager to Implement I/O 7. Co-operate with the Memory Manager to Implement Memory Space

The Abstract Machine Interface Application Program Abstract Machine Instructions Trap Instruction Supervisor Mode Instructions fork() create() open() OS User Mode Instructions User Mode Instructions

Context Switching-Abstract Machine switching Executable Memory Initialization 1 Process Manager 9 6 4 2 5 8 3 7 Interrupt Interrupt Handler P1 P2 Pn

OS Families-Example POSIX Standard Description Release POSIX.1-1988 system interfaces and headers SunOS 4.1 POSIX.1-1990 POSIX.1-1988 update Solaris 2.0 POSIX.1b-1993 real-time extensions Solaris 2.4 POSIX.1c-1996 threads extensions Solaris 2.6 POSIX.2-1992 shell and utilities Solaris 2.5 POSIX.2a-1992 interactive shell and utilities Solaris 2.5

Process Descriptors OS creates/manages process abstraction Descriptor is data structure for each process Register values Logical state Type & location of resources it holds List of resources it needs Security keys etc. (see Table 6.1 and the source code of your favorite OS)

Windows NT Process Descriptor EPROCESS … void *UniqueProcessId; NT Executive KPROCESS … uint32 KernelTime; uint32 UserTime; Byte state; NT Kernel

Windows NT Process Descriptor (2) Kernel process object including: Pointer to the page directory Kernel & user time Process base priority Process state List of the Kernel thread descriptors that are using this process

Windows NT Process Descriptor (3) Parent identification Exit status Creation and termination times. Memory status Security information executable image Process priority class used by the thread scheduler. A list of handles used by this process A pointer to Win32-specific information

Windows NT Thread Descriptor EPROCESS KPROCESS ETHREAD KTHREAD NT Kernel NT Executive

Creating a Process in UNIX pid = fork(); UNIX kernel Process Table … Process Descriptor

Creating a Process in NT CreateProcess(…); Win32 Subsystem ntCreateProcess(…); … ntCreateThread(…); NT Executive Handle Table NT Kernel … Process Descriptor

Windows NT Handles

Simple State Diagram Request Done Running Request Schedule Start Allocate Blocked Ready

UNIX State Transition Diagram Request Wait by parent Done Running zombie Schedule Request Sleeping I/O Request Start Allocate Runnable I/O Complete Resume Traced or Stopped Uninterruptible Sleep

Windows NT Thread States CreateThread Terminated Initialized Reinitialize Activate Dispatch Exit Wait Waiting Ready Running Wait Complete Wait Complete Select Preempt Transition Dispatch Standby

Resources Resource: Anything that a process can request, then be blocked because that thing is not available. R = {Rj | 0  j < m} = resource types C = {cj  0 |  RjR (0  j < m)} = units of Rj available Reusable resource: After a unit of the resource has been allocated, it must ultimately be released back to the system. E.g., CPU, primary memory, disk space, … The maximum value for cj is the number of units of that resource Consumable resource: There is no need to release a resource after it has been acquired. E.g., a message, input data, … Notice that cj is unbounded.

Using the Model There is a resource manager, Mgr(Rj) for every Rj pi can only request ni  cj units of reusable Rj pi can request unbounded # of units of consumable Rj Process pi can request units of Rj if it is currently running request Mgr(Rj) can allocate units of Rj to pi allocate Mgr(Rj) Process

A Generic Resource Manager Blocked Processes Policy Process request() Process release() Resource Pool

Process Hierarchies Parent-child relationship may be significant: parent controls children’s execution Request Done Running Yield Suspend Request Schedule Suspend Start Ready-Active Activate Ready-Suspended Allocate Allocate Suspend Blocked-Active Blocked-Suspended Activate

Process Manager Overview Program Process Abstract Computing Environment Deadlock Process Description File Manager Protection Synchronization Device Manager Memory Manager Resource Manager Scheduler Devices Memory CPU Other H/W

UNIX Organization Process Libraries Process Process System Call Interface Deadlock Process Description File Manager Protection Synchronization Device Manager Memory Manager Resource Manager Scheduler Monolithic Kernel Devices Memory CPU Other H/W

Windows NT Organization Process Process T T Process T T T T Libraries T T T Subsystem Subsystem Subsystem User I/O Subsystem NT Executive NT Kernel Hardware Abstraction Layer Processor(s) Main Memory Devices