Question

What's the high resolution time axis behavior of TCL 'exec ' ? I understand that a 'fork' command will be used which will at first create a copy of the memory image of the process and then proceed.

Here's the motivation for my question:

A user gave me following observation. A 64 GB machine has a TCL based tool interface running with 60GB memory used. (let's assume swap is small). At the TCL prompt he gives 'exec ls' and the process crashes with a memory error.

You insight is much appreciated. Thanks, Gert

Answer 1

exec命令将在内部调用fork()系统调用。这通常没问题，但是当操作系统配置为不交换并且原始Tcl进程非常大时（或者如果有很少的slop空间;它当然取决于实际情况）可能会耗尽内存。

我减少内存使用量的想法是使用vfork()（通过修补tclUnixPipe.c;您可以在makefile中定义USE_VFORK以启用它，而且我不会这样做。知道为什么不能更广泛地使用）或者在早期创建一个帮助程序（在使用大量内存之前），这将在主进程上执行exec＆＃39;代表。以下是如何做到后一种选择：

# This is setup done at the start
set forkerProcess [open "|tclsh" r+]
fconfigure $forkerProcess -buffering line -blocking 0
puts $forkerProcess {
    fconfigure stdout -buffering none
    set tcl_prompt1 ""
    set tcl_prompt2 ""
    set tcl_interactive 0
    proc exechelper args {
        catch {exec {*}$args} value options
        puts [list [list $value $options]]
    }
}
# TRICKY BIT: Yield and drain anything unwanted
after 25
read $forkerProcess

# Call this, just like exec, to run programs without memory hazards
proc do-exec args {
    global forkerProcess
    fconfigure $forkerProcess -blocking 1
    puts $forkerProcess [list exechelper {*}$args]
    set result [gets $forkerProcess]
    fconfigure $forkerProcess -blocking 0
    while {![info complete $result]} {
        append result \n [read $forkerProcess]
    }
    lassign [lindex $result 0] value options
    return -options $options $value
}

Time resolved memory footprint of TCL exec

1 个答案: