Annotation of embedaddon/libpdel/util/paction.3, revision 1.1
1.1 ! misho 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"
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! 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,
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! 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
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! 31: .\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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! 34: .\" THE POSSIBILITY OF SUCH DAMAGE.
! 35: .\"
! 36: .\" Author: Archie Cobbs <archie@freebsd.org>
! 37: .\"
! 38: .\" $Id: paction.3,v 1.4 2004/06/02 17:24:39 archie 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
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