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ChorusOS 5.0 Features and Architecture Overview

Optional Actor Management Services

User Mode (USER_MODE)

The USER_MODE feature enables support for user mode actors that require direct access to the microkernel API.

This feature provides support for unprivileged actors, running in separate virtual user address spaces (when available).

USER_MODE is used in all memory models.

For details, see USER_MODE(5FEA).

GZ_FILE

The GZ_FILE feature enables dynamically loaded actors and dynamic libraries to be uncompressed at load time, prior to execution. This minimizes the space required to store these compressed files and the download time.

The GZ_FILE feature has no API. It is based on the gunzip tool. Thus, an executable file compressed on the host system using the gzip command (whose suffix is .gz) will be recognized automatically as a compressed executable file or dynamic library and uncompressed by the system at load time.

For details, see GZ_FILE(5FEA).

Dynamic Libraries (DYNAMIC_LIB)

The DYNAMIC_LIB feature provides support for dynamic libraries within the ChorusOS operating system. These libraries are loaded and mapped within the actor address space at execution time. Symbol resolution is performed at library load time. This feature also enables a running actor to ask for a library to be loaded and installed within its address space, and then to resolve symbols within this library. The feature handles dependencies between libraries.

The DYNAMIC_LIB feature API is summarized in the following table.

Function 

Description 

dladdr()

Translate address into symbolic information 

dlclose()

Close a dynamic library 

dlerror()

Get diagnostic information 

dlopen()

Gain access to a dynamic library file 

dlsym()

Get the address of a symbol in a dymanic library 

For details, see DYNAMIC_LIB(5FEA).

Shared Libraries

Shared libraries are similar to dynamic libraries. Dynamic libraries are shared if there is no relocation in the text section. To make a dynamic library sharable, you must compile all the objects belonging to the shared library with the FPIC = ON imake definition. The ChorusOS operating system also provides Imake rules to create shared libraries.

The API which applies to dynamic libraries also applies to shared libraries. The ChorusOS operating system provides the following shared libraries for user actors and processes:

Library 

Description 

libc.so

Basic library routines 

libnsl.so

RPC library and network resolution routine (gethostbyname(), and so on)

librpc.so

RPC library only 

libpthread.so

POSIX thread library 

libpam.so

Password management routines 

Thread Synchronization (MONITOR)

Concurrent threads are synchronized by monitors. A monitor is a set of functions in which only one thread may execute at a time. It is possible for a thread running inside a monitor to suspend its execution so that another thread may enter the monitor. The initial thread waits for the second one to notify it (for example, that a resource is now available) and then to exit the monitor.

MONITOR API

The MONITOR API is summarized in the following table:

Function 

Description 

monitorGet()

Obtains the lock on the given monitor 

monitorInit()

Initializes the given monitor 

monitorNotify()

Notifies one thread waiting in monitorWait()

monitorNotifyAll()

Notifies all threads waiting in monitorWait()

monitorRel()

Releases a lock on a given monitor 

monitorWait()

Causes a thread that owns the lock on the given monitor to suspend itself until it receives notification from another thread