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modified post a5 by Anonymous on Mon 18th Nov 2019 17:45
original post 239810184c by Anonymous on Mon 18th Nov 2019 16:16
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#!/usr/bin/ksh93

1	1		#!/usr/bin/ksh93
2	2
3	3		# should work for ksh88/ksh93/bash4
4	4
5	5		########################################################################
6	6		# #
7	7		# This software is part of the ast package #
8	8		# Copyright (c) 2019 Roland Mainz #
9	9		# and is licensed under the #
10	10		# Eclipse Public License, Version 1.0 #
11	11		# by AT&T Intellectual Property #
12	12		# #
13	13		# A copy of the License is available at #
14	14		# http://www.eclipse.org/org/documents/epl-v10.html #
15	15		# (with md5 checksum b35adb5213ca9657e911e9befb180842) #
16	16		# #
17	17		# #
18	18		# Roland Mainz <roland.mainz@nrubsig.org> #
19	19		# #
20	20		########################################################################
21	21
22	22		#
23	23		# Copyright (c) 2019, Roland Mainz. All rights reserved.
24	24		#
25	25
26	26		#
27	27		# shsemaphore.sh - wait until <n> customers are waiting
28	28		# at the semaphore
29	29		#
30	30		# Usage:
31	31		# 1. init semaphore ("mysemaname" is the 'semaphore address')
32	32		# $ shsemaphore.sh init mysemaname
33	33		#
34	34		# 2. let two semaphore customers (names are 'Bear' and 'Fox')
35	35		# wait for each other:
36	36		# $ shsemaphore.sh wait mysemaname Bear 2 &
37	37		# $ shsemaphore.sh wait mysemaname Fox 2
38	38		#
39	39		# 3. Cleanup all the mess if you are really done:
40	40		# $ shsemaphore.sh cleanup mysemaname
41	41		#
42	42
43	43		# POSIX path for mkdir, ls, rm, rmdir ...
44	44		export PATH='/bin:/usr/bin'
45	45
46	46		# constants
47	47		typeset -r SEMA_BASE_DIR='/tmp/'
48	48
49	49		# arguments
50	50		typeset sema_cmd="$1"
51	51		typeset sema_address="${SEMA_BASE_DIR}/shsemaphore_$2"
52	52		typeset sema_name="${sema_address}/$3"
53	53		typeset -i sema_count="$4"
54	54
55	55		# Debug:
56	56		#printf "cmd=%s, address=%s, name=%s, count=%d\n" \
57	57		# "${sema_cmd}" "${sema_address}" "${sema_name}" "${sema_count}"
58	58
59	59		function sema_cleanup
60	60		{
61	61		rm -Rf "${sema_address}"
62	62		}
63	63
64	64		function sema_init
65	65		{
66	66		if [[ -z "$SEMA_BASE_DIR" \|\| -z "$sema_address" ]] ; then
67	67		printf "%s: Illegal arguments.\n" "$0" 1>&2
68	68		return 1
69	69		fi
70	70
71	71		mkdir -p "${SEMA_BASE_DIR}"
72	72
73	73		sema_cleanup
74	74		mkdir "${sema_address}"
75	75		}
76	76
77	77		function sema_wait
78	78		{
79	79		typeset IFS
80	80
81	81		if [[ -z "$SEMA_BASE_DIR" \|\| -z "$sema_address" \|\| -z "$sema_name" \|\| -z "$sema_count" ]] ; then
82	82		printf "%s: Illegal arguments.\n" "$0" 1>&2
83	83		return 1
84	84		fi
85	85
86	86		if ! mkdir "${sema_name}" ; then
87	87		printf "%s: Count not set name.\n" "$0" 1>&2
88	88		return 1
89	89		fi
90	90
	91	+	# is semaphore still valid ?
91	94		IFS=$'\n'
92	95		while (( 1 )) ; do
93		-	# we count '.' and '..', too
	96	+	# 1. we rely on shell globing to avoid \|fork()\|/\|exec()\|
94		-	sfiles=( $(ls -1a "${sema_address}" 2>'/dev/null') )
	97	+	# for ls(1)
	98	+	# 2. we count '.' and '..', too. Both special dirs
95	102
	103	+	# Debug:
96	106		# semaphore condition fullfilled ?
97	107		(( ${#sfiles[@]} >= (sema_count+2) )) && return 0
98	108
99	109		# semaphore gone ?
100		-	(( ${#sfiles[@]} < 2 )) && return 4
	110	+	# In that case we get only two entries from globbing
	111	+	# above, one for '/' and one for './'
101	113
102	114		sleep 2
103	115		done
104	116		# notreached
105	117		}
106	118
107	119		# main
108	120		case "${sema_cmd}" in
109	121		'init')
110	122		sema_init
111	123		exit $?
112	124		;;
113	125		'wait')
114	126		sema_wait
115	127		exit $?
116	128		;;
117	129		'cleanup')
118	130		sema_cleanup
119	131		exit $?
120	132		;;
121	133		*)
122	134		printf "%s: Unknown command.\n" "$0" 1>&1
123	135		exit 1
124	136		;;
125	137		esac
126	138
127	139