Common Software Services

1
Common Software Services

• The Globus Project
• Argonne National LaboratoryUSC Information
  Sciences Instutute
• http//www.globus.org/

2
Common Services

• Portability Aids Assist in writing portable
  Makefiles, shell scripts, and programs
• Collection of fundamental modules
• Module activation/deactivation
• Portable thread library (POSIX subset)
• Thread-safe and portable libc wrappers
• Timed and periodic callbacks
• Data object and error object management
• Modules to manipulate lists, fifos, URLs,
• The rest of the Globus Toolkit relies on
  globus_common
• User can/should use these for maximum portability
  and convenience

3
Writing Portable Makefiles

• Each development flavor has a file for inclusion
  in makefiles etc/makefile_header
• defines settings used for CC, LD, etc.
• three important defintions
• CFLAGS ex -g -thread
• LDFLAGS ex -L/usr/local/ssl/lib
• LIBS ex -lpthreads -lsocket -lssl
• also, the three definitions for each module is
  defined
• GLOBUS_COMMON_CFLAGS,LDFLAGS,LIBS
• GLOBUS_DUROC_RUNTIME_CFLAGS,LDFLAGS,LIBS
• etc.

4
Writing portable shell scripts

• Need to be able to write scripts that work
  anywhere, regardless of your path settings
• The globus-sh-tools file defines variables with
  complete paths to gt100 commonlyused programs
  (Bourne shell syntax)
• GLOBUS_SH_LS/bin/ls
• GLOBUS_SH_GREP/usr/bin/grep
• This can be sourced in your /bin/sh script
• . GLOBUS_TOOLS_PATH/libexec/globus-sh-tools
• The variables can then used in your script
• GLOBUS_SH_GREP -i grid mydocument gt outputfile

5
globus_config.h

• When Globus Toolkit is built, it runs extensive
  configuration checks. Much of this knowledge is
  stored in a globus_config.h file, which can be
  used by any program
• Architecture type
• Availability of particular header files
• Availability of particular functions
• Non-standard types or functions

6
Activation and Deactivation

• globus_module_()
• Functions for activation (initialization) and
  deactivation (shutdown)
• Support for multiple independent activations and
  deactivations of a module through reference
  counting
• Support for dependencies amongst modules
• Support for thread-safe initialization
• Modules can use atexit()...

7
globus_module_activate()

• This function must be called, passing it the
  appropriate module descriptor, before calling any
  other functions in that module
• globus_module_activate(GLOBUS_NEXUS_MODULE)
• Returns GLOBUS_SUCCESS if the module was
  successfully activated
• Simultaneous activations of the same module are
  handled correctly through serialization
• The activated module is responsible for
  recursively activating all modules that it
  requires

8
globus_module_deactivate()

• There must be a matching deactivation for each
  and every activation
• globus_module_deactivate(GLOBUS_NEXUS_MODULE)
• Returns GLOBUS_SUCCESS if the module was
  successfully activated
• Can re-activate a module after it has been
  deactivated
• For convenience, can deactivate all at once
• globus_module_deactivate_all()

9
Threads

• globus_thread_(), globus_mutex_(),
  globus_cond_()
• Simple POSIX threads (pthreads) subset
• Same arguments and semantics as pthreads
• Simply change pthread to globus or
  globus_thread in the function name
• Provides portability to pre-standard pthread
  libraries, and non-pthread based systems
• Simple pass-through on systems with standard
  pthreads
• Co-exists with programs using pthreads directly

10
Thread Management Functions

• Subset of pthreads for creating and managing
  threads
• globus_thread_create()
• globus_thread_exit()
• globus_thread_self()
• globus_thread_equal()
• globus_thread_once()
• globus_thread_yield()
• globus_threadattr_init(), _destroy()
• globus_threadattr_setstacksize(),

11
Thread Specific Storage

• Pthread functions for storing per-thread data
• globus_thread_key_create()
• globus_thread_key_delete()
• globus_thread_setspecific()
• globus_thread_getspecific()
• These work with or without threads

12
Mutual Exclusion

• Pthread functions for mutual exclusion
• globus_mutex_init()
• globus_mutex_destroy()
• globus_mutex_lock()
• globus_mutex_trylock()
• globus_mutex_unlock()
• These work with or without threads

13
Conditions

• Condition variables for signaling between threads
• globus_cond_init()
• globus_cond_destroy()
• globus_cond_wait()
• globus_cond_signal()
• globus_cond_broadcast()
• These work with our without threads

14
Thread Block Callbacks

• Layer on top of pthread functions, which allows
  callbacks to be triggered when a thread blocks
  via globus_cond_wait()
• globus_thread_blocking_callback_push()
• globus_thread_blocking_callback_pop()
• globus_thread_blocking_callback_enable()
• globus_thread_blocking_callback_disable()
• globus_thread_blocking_will_block()
• Used by common callback library

15
Threaded vs Non-threaded

• Globus supports pthreads, cthreads, Solaris
  threads, and sproc
• Also supports non-threaded applications
• Most thread-related functions are stubbed out
• If you write code carefully which uses the mutex,
  cond, and thread specific storage functions, if
  should work both threaded and non-threaded
• Most Globus Toolkit APIs use an event driven
  approach, which works well either with or without
  threads

16
globus_libc

• Wrappers around standard libc functions
• Thread safe, even if underlying libc is not
• Caveat Application must also use globus_libc to
  ensure thread safety
• Same interface for threaded and non-threaded
• POSIX reentrant functions (_r()) always work
• Example globus_libc_gethostbyname_r()
• Fixes or enhances some functions
• Example globus_libc_gethostname() tries to
  figure out a fully qualified hostname despite
  system configuration

17
Callbacks

• Driver for timed and periodic callbacks
• globus_callback_register_oneshot()
• globus_callback_register_periodic()
• globus_callback_unregister()
• globus_callback_poll()
• All modules rely on this for periodic polling
• Uses threads where possible
• Uses thread blocking callbacks to guarantee
  progress even when callback blocks

18
Convenience Modules

• globus_common also contains a small set of
  convenience modules
• globus_fifo First-In-First-Out queue
• globus_hashtable Hashtable
• globus_list List functions
• globus_symboltable Symbol table management
• globus_url URL parsing
• globus_strptime Y2K-compliant strptime()
• globus_object
• globus_error

19
globus_common exercises

• Go to the common subdirectory
• View the layout of the Makefile
• View the documentation on the web
• Unfortunately, globus_common docs are currently
  incomplete, but what we will cover today is
  available athttp//www.globus.org/common/
• Follow instructions in the file README