2010-05-16

ptrace 在 linux 和 freebsd 下的若干区别 | Several differences of ptrace between Linux and FreeBSD

最近要把一个程序移植到Debian-kfreebsd上,并不如想象中的顺利。
主要是ptrace在两个平台上不太一样。

首先是宏定义,linux底下都叫PTRACE_*,freebsd上都是PT_*。这个也许不算什么

然后是ptrace函数的参数,主要是value这个,linux下面是long很好用,但是freebsd下是int,这样64位的时候就有些问题。

但是freebsd的ptrace有个更好用的操作PT_IO,可以自定义读写长度,而linux底下没有,要自己搞。

最后一个,花了我很长时间才解决的,是CONTINUE这个操作,linux下面addr这个参数是被忽略的,直接从中断的地方继续;但是freebsd下面则可以利用这个参数指定从哪里继续,如果希望从中断的地方继续,则指定为1即可。

目前只遇到这些,从这些方面来看,还是freebsd的接口更好用一些。



Recently I've been porting a software from Linux to Debian-kfreebsd, but it's not as easy as I had expected. The problem is the interface of ptrace is not exactly the same between linux and kfreebsd.

The first is the names of the macros, which are PTRACE_* under linux and PT_* under freebsd.

Secondly the function `ptrace' is not the same, the parameter `value' is `long' under Linux, but `int' under freebsd, so it seems that there'll be a problem on 64 bit freebsd.

However, there's another operation called PT_IO under freebsd, using which we can specify the number of bytes we want to read or write.

The last and the most annoying one I've met, is the parameter `addr' for the CONTINUE operations. Under linux this parameter is ignored, and the child process will continue at where it had been interrupted; but under freebsd, we can specify this location by setting this parameter, and we can also let it continue at where it had been interrupted but setting the value to 1.

Now that's all for my program, and it seems that the interface under freebsd is better than that under linux.

2010-05-03

并行运行多进程的Bash脚本 | A srcipt for running processes in parallel in Bash

原文:http://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/

技巧是控制了最大并发数目,当前并发数过大时,等待有进程退出才开始下一个。

我现在正在写的脚本里正需要这个,借鉴过来


#!/bin/bash
NUM=0
QUEUE=""
MAX_NPROC=2 # default
REPLACE_CMD=0 # no replacement by default
USAGE="A simple wrapper for running processes in parallel.
Usage: `basename $0` [-h] [-r] [-j nb_jobs] command arg_list
-h Shows this help
-r Replace asterix * in the command string with argument
-j nb_jobs Set number of simultanious jobs [2]
Examples:
`basename $0` somecommand arg1 arg2 arg3
`basename $0` -j 3 \"somecommand -r -p\" arg1 arg2 arg3
`basename $0` -j 6 -r \"convert -scale 50% * small/small_*\" *.jpg"

function queue {
QUEUE="$QUEUE $1"

NUM=$(($NUM+1))
}

function regeneratequeue {
OLDREQUEUE=$QUEUE
QUEUE=""
NUM=0
for PID in $OLDREQUEUE
do
if [ -d /proc/$PID ] ; then
QUEUE="$QUEUE $PID"
NUM=$(($NUM+1))
fi
done
}

function checkqueue {
OLDCHQUEUE=$QUEUE
for PID in $OLDCHQUEUE
do
if [ ! -d /proc/$PID ] ; then
regeneratequeue # at least one PID has finished
break
fi
done
}

# parse command line
if [ $# -eq 0 ]; then # must be at least one arg
echo "$USAGE" >&2
exit 1
fi

while getopts j:rh OPT; do # "j:" waits for an argument "h" doesnt
case $OPT in
h) echo "$USAGE"

exit 0 ;;
j) MAX_NPROC=$OPTARG ;;
r) REPLACE_CMD=1 ;;
\?) # getopts issues an error message
echo "$USAGE" >&2
exit 1 ;;
esac
done

# Main program
echo Using $MAX_NPROC parallel threads
shift `expr $OPTIND - 1` # shift input args, ignore processed args
COMMAND=$1
shift

for INS in $* # for the rest of the arguments
do
# DEFINE COMMAND
if [ $REPLACE_CMD -eq 1 ]; then
CMD=${COMMAND//"*"/$INS}
else
CMD="$COMMAND $INS" #append args
fi
echo "Running $CMD"

$CMD &
# DEFINE COMMAND END

PID=$!
queue $PID

while [ $NUM -ge $MAX_NPROC ]; do
checkqueue
sleep 0.4
done
done
wait # wait for all processes to finish before exit






Original posted at: http://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/

This script will run multiple process in background concurrently, while the maximum number of running processed is under control. When there are already too many running processes, a new one will wait until one process finished.

I just need this trick in my project, so I copied it here.

(See codes above)