令人惊奇的gdb和pstack

pstack竟然是一个shell脚本，核心是调用gdb的thread apply all bt查看进程的所有线程的堆栈，之后用sed正则展示线程堆栈信息。

/proc/pid/exe是一个指向可执行文件的软连接。

#!/bin/sh

if test $# -ne 1; then

    echo "Usage: `basename $0 .sh` <process-id>" 1>&2

    exit 1

fi

if test ! -r /proc/$1; then

    echo "Process $1 not found." 1>&2

    exit 1

fi

# GDB doesn't allow "thread apply all bt" when the process isn't

# threaded; need to peek at the process to determine if that or the

# simpler "bt" should be used.

backtrace="bt"

if test -d /proc/$1/task ; then

    # Newer kernel; has a task/ directory.

    if test `/bin/ls /proc/$1/task | /usr/bin/wc -l` -gt 1 2>/dev/null ; then

        backtrace="thread apply all bt"

    fi

elif test -f /proc/$1/maps ; then

    # Older kernel; go by it loading libpthread.

    if /bin/grep -e libpthread /proc/$1/maps > /dev/null 2>&1 ; then

        backtrace="thread apply all bt"

    fi

fi

GDB=${GDB:-/usr/bin/gdb}

if $GDB -nx --quiet --batch --readnever > /dev/null 2>&1; then

    readnever=--readnever

else

    readnever=

fi

# Run GDB, strip out unwanted noise.

$GDB --quiet $readnever -nx /proc/$1/exe $1 <<EOF 2>&1 | 

set width 0

set height 0

set pagination no

$backtrace

EOF

/bin/sed -n \

    -e 's/^(gdb) //' \

    -e '/^#/p' \

    -e '/^Thread/p'