Return to paction.3 CVS log

Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / libpdel / util

libpdel

    1: .\" Copyright (c) 2001-2002 Packet Design, LLC.
    2: .\" All rights reserved.
    3: .\" 
    4: .\" Subject to the following obligations and disclaimer of warranty,
    5: .\" use and redistribution of this software, in source or object code
    6: .\" forms, with or without modifications are expressly permitted by
    7: .\" Packet Design; provided, however, that:
    8: .\" 
    9: .\"    (i)  Any and all reproductions of the source or object code
   10: .\"         must include the copyright notice above and the following
   11: .\"         disclaimer of warranties; and
   12: .\"    (ii) No rights are granted, in any manner or form, to use
   13: .\"         Packet Design trademarks, including the mark "PACKET DESIGN"
   14: .\"         on advertising, endorsements, or otherwise except as such
   15: .\"         appears in the above copyright notice or in the software.
   16: .\" 
   17: .\" THIS SOFTWARE IS BEING PROVIDED BY PACKET DESIGN "AS IS", AND
   18: .\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, PACKET DESIGN MAKES NO
   19: .\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING
   20: .\" THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED
   21: .\" WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
   22: .\" OR NON-INFRINGEMENT.  PACKET DESIGN DOES NOT WARRANT, GUARANTEE,
   23: .\" OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS
   24: .\" OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY,
   25: .\" RELIABILITY OR OTHERWISE.  IN NO EVENT SHALL PACKET DESIGN BE
   26: .\" LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE
   27: .\" OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT,
   28: .\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL
   29: .\" DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF
   30: .\" USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF
   31: .\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   32: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
   33: .\" THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF
   34: .\" THE POSSIBILITY OF SUCH DAMAGE.
   35: .\"
   36: .\" Author: Archie Cobbs <archie@freebsd.org>
   37: .\"
   38: .\" $Id: paction.3,v 1.1.1.1 2012/02/21 23:25:53 misho Exp $
   39: .\"
   40: .Dd April 22, 2002
   41: .Dt PACTION 3
   42: .Os
   43: .Sh NAME
   44: .Nm paction
   45: .Nd actions in a separate thread
   46: .Sh LIBRARY
   47: PDEL Library (libpdel, \-lpdel)
   48: .Sh SYNOPSIS
   49: .In sys/types.h
   50: .In pthread.h
   51: .In pdel/util/paction.h
   52: .Ft int
   53: .Fn paction_start "struct paction **actionp" "pthread_mutex_t *mutex" "paction_handler_t *handler" "paction_finish_t *finish" "void *arg"
   54: .Ft void
   55: .Fn paction_cancel "struct paction **actionp"
   56: .Sh DESCRIPTION
   57: These functions provide support for
   58: .Em actions ,
   59: which are simply function invocations that happen in separate threads.
   60: This is just a simplified API for spawning and cancelling threads with
   61: built-in support for mutex locking and avoiding certain race conditions.
   62: .Pp
   63: .Fn paction_start
   64: creates a new action and stores a pointer to the action, represented by a
   65: .Li "struct paction" ,
   66: in
   67: .Fa "*actionp" .
   68: The creation of an action results in
   69: .Fn handler
   70: being invoked in a new thread.
   71: .Fn paction_cancel
   72: cancels an action by canceling its associated thread.
   73: In any case, when the action has completed,
   74: .Fn finish
   75: is invoked.
   76: If the action was not canceled via
   77: .Fn paction_cancel ,
   78: then
   79: .Fa "*mutex"
   80: is acquired before
   81: .Fn finish
   82: is invoked and released afterward.
   83: If 
   84: .Fn paction_cancel
   85: was called, then the mutex is not acquired for
   86: .Fn finish .
   87: The
   88: .Fa was_canceled
   89: argument to
   90: .Fn finish
   91: reflects this.
   92: .Pp
   93: .Fa handler
   94: and
   95: .Fa finish
   96: must be pointers to functions having these types:
   97: .Pp
   98: .Bd -literal -compact -offset 3n
   99: typedef void paction_handler_t(void *arg);
  100: typedef void paction_finish_t(void *arg, int was_canceled);
  101: .Ed
  102: .Pp
  103: When
  104: .Fn paction_start
  105: is invoked,
  106: .Fa "*actionp"
  107: must be
  108: .Dv NULL .
  109: As long as the action is still in progress (i.e.,
  110: .Fn finish
  111: has not yet been invoked),
  112: .Fa "*actionp"
  113: will be non-NULL.
  114: When the action completes or is canceled,
  115: .Fa "*actionp"
  116: is set to
  117: .Dv NULL
  118: again.
  119: Therefore,
  120: .Fa "*actionp"
  121: must remain valid and unmodified for the duration of the action,
  122: and can be used as an indicator of whether the action has completed.
  123: .Pp
  124: .Fn paction_cancel
  125: cancels an outstanding action.
  126: This results in the action thread being canceled at the next
  127: cancellation point.
  128: Therefore,
  129: .Fn handler
  130: may need to register thread cleanup hooks in order to free
  131: any allocated resources in the case of cancellation.
  132: Upon return,
  133: .Fa "*actionp"
  134: is set to
  135: .Dv NULL .
  136: If
  137: .Fa "*actionp"
  138: is already
  139: .Dv NULL
  140: when
  141: .Fn paction_cancel
  142: is invoked, nothing happens.
  143: .Pp
  144: In any case,
  145: .Fn finish
  146: is invoked when the action terminates.
  147: There are two reasons for an action terminating:
  148: either the action terminated normally, or
  149: .Fn paction_cancel
  150: was invoked.
  151: If the action terminated normally,
  152: .Fa "*mutex"
  153: is locked,
  154: .Fa "*actionp"
  155: is set to
  156: .Dv NULL ,
  157: and
  158: .Fn finish
  159: is invoked with
  160: .Fa was_canceled
  161: set to zero.
  162: When
  163: .Fn finish
  164: returns
  165: .Fa *mutex
  166: is unlocked.
  167: .Pp
  168: If the action was canceled by
  169: .Fn paction_cancel ,
  170: then neither
  171: .Fa "mutex"
  172: nor
  173: .Fa "actionp"
  174: are dereferenced;
  175: .Fn final
  176: is simply called with
  177: .Fa was_canceled
  178: set to non-zero.
  179: Note that
  180: .Fa "*actionp"
  181: will have already been set to
  182: .Dv NULL
  183: previously by
  184: .Fn paction_cancel .
  185: .Pp
  186: Cancelling the action thread directly via
  187: .Xr pthread_cancel 3
  188: is treated just as if
  189: .Fn handler
  190: returned early; i.e., the first case above.
  191: .\"
  192: .Ss Synchronization
  193: .\"
  194: There are inherent race conditions between an action's
  195: .Fn finish
  196: function being invoked and reading the value of
  197: .Fa "*actionp"
  198: or canceling the action with
  199: .Fn paction_cancel .
  200: The
  201: .Fa "*mutex"
  202: should be used to avoid these problems by using it to
  203: protect
  204: .Fa "*actionp" .
  205: .Pp
  206: The user code should acquire
  207: .Fa "*mutex"
  208: before calling
  209: .Fn paction_start
  210: or
  211: .Fn paction_cancel ,
  212: or before accessing
  213: .Fa "*actionp" .
  214: If this protocol is followed, then
  215: .Fa "*actionp"
  216: will be non-NULL if and only if the action is still pending, i.e.,
  217: .Fn finish
  218: has not yet been invoked.
  219: In addition, the
  220: .Fa was_canceled
  221: argument will always be accurate, i.e., be non-zero if and only if
  222: .Fn paction_cancel
  223: was called to cancel the action.
  224: .Pp
  225: Finally,
  226: .Fa "mutex"
  227: and
  228: .Fa "actionp"
  229: will not be dereferenced after a call to
  230: .Fn paction_cancel ,
  231: so it is always safe to destroy the memory pointed to by
  232: .Fa "mutex"
  233: and
  234: .Fa "actionp"
  235: after calling
  236: .Fn paction_cancel .
  237: However,
  238: .Fa arg
  239: must remain valid until
  240: .Fn finish
  241: is invoked, which may occur
  242: .Em after
  243: .Fn paction_cancel
  244: returns; alternatively,
  245: .Fn finish
  246: must not dereference
  247: .Fa arg
  248: if
  249: .Fa was_canceled
  250: is non-zero.
  251: .Sh RETURN VALUES
  252: .Fn paction_start
  253: returns -1 if there is an error, with
  254: .Va errno
  255: set appropriately.
  256: In particular, if
  257: .Fa "*actionp"
  258: is not equal to
  259: .Dv NULL ,
  260: then
  261: .Va errno
  262: will be set to
  263: .Er EBUSY .
  264: .Sh SEE ALSO
  265: .Xr libpdel 3 ,
  266: .Xr pevent 3 ,
  267: .Xr pthread_cancel 3 ,
  268: .Xr pthread_create 3
  269: .Sh HISTORY
  270: The PDEL library was developed at Packet Design, LLC.
  271: .Dv "http://www.packetdesign.com/"
  272: .Sh AUTHORS
  273: .An Archie Cobbs Aq archie@freebsd.org