Running a program which accepts stdin/stdout in Node.js causes it to consume 100% CPU+RAM

[shlomif]

Hi,

I am trying to build perl5 using emscripten and so far I have this:

https://github.com/shlomif/perl5-build-using-emscripten

However I'm running into problem with the perl "tryp.c" example, and could not find anything in a web search.

Please run the following script in an empty directory with "emcc" and "node" (from node-js) in the path:

#!/bin/bash

cat <<EOF > tryp.c
#include <stdio.h>
int
main(int argc, char **argv)
{
    char buf[1024];
    int i;
    char *bp = buf;
    while (1) {
    while ((i = getc(stdin)) != -1
           && (*bp++ = i) != '\n'
           && bp < &buf[1024])
    /* DO NOTHING */ ;
    *bp = '\0';
    fprintf(stdout, "%s", buf);
    fflush(stdin);
    if (i == -1)
        return 0;
    bp = buf;
    }
}
EOF

emcc --jcache -s TOTAL_MEMORY=134217728 -std=gnu99 -O2 -I . -m32 -o tryp.js tryp.c
node tryp.js

node ends up consuming 100% of CPU and gradually consumes more and more RAM. Can this be fixed?

Update: I am on Mageia Linux 3 Cauldron ( http://www.mageia.org/en/ ) with clang-3.2-5.mga3 , llvm-3.2-5.mga3 , nodejs-0.10.3-2.mga3 , etc.

Thanks!

-- @shlomif

[shlomif]

Update: I am able to reproduce it on an Arch Linux x86-64 latest VM.

[kripken]

The problem is that there doesn't seem to be a way to read a line of input from stdin in a synchronous way, in node. In v8 and spidermonkey shells we can do that by calling readline() simply enough ;) In node I saw various suggestions for how to do it, but none worked for me.

If we find out how to do it, then basically in src/shell.js we would define readline() in the node case using the solution.

[shlomif]

@kripken : thanks for the explanation - I see.I guess I can try it using v8 or spidermonkey for now.

[shlomif]

Hi @kripken ,

With this script that uses spidermonkey's "js" instead of "node", the JS program gets stuck. The equivalent C program ("gcc tryp.c") exits after a while:

#!/bin/bash

cat <<'EOF' > tryp.c
#include <stdio.h>
int
main(int argc, char **argv)
{
    char buf[1024];
    int i;
    char *bp = buf;
    while (1) {
    while ((i = getc(stdin)) != -1
           && (*bp++ = i) != '\n'
           && bp < &buf[1024])
    /* DO NOTHING */ ;
    *bp = '\0';
    fprintf(stdout, "%s", buf);
    fflush(stdin);
    if (i == -1)
        return 0;
    bp = buf;
    }
}
EOF

emcc --jcache -s TOTAL_MEMORY=134217728 -std=gnu99 -O2 -I . -m32 -o tryp.js tryp.c
# node tryp.js
perl -E 'print ("x\n" x 100)' | js tryp.js

[kripken]

Isn't that the same program as before? In js and in native, it waits for lines of input and repeats them, for me.

[shlomif]

@kripken : sorry for the late response. Yes , it is the same program, but:

perl -e 'print ("x\n" x 100)' | ./a.out

exits after a short while, while:

perl -e 'print ("x\n" x 100)' | js tryp.js 

gets stuck in an infinite loop consuming a lot of CPU and some RAM.

[kripken]

forgive my ignorance ;) but what does that perl do? how is it different than interactively entering input (which seems to work)?

[shlomif]

Hi @kripken ,

what this perl code does is emit 100 lines containing "x" (and a newline) followed by and "end-of-stream". print emits output to the string, and "x" is the repeat operator - http://perl-begin.org/tutorials/perl-for-newbies/part1/#page--arrays--x--PAGE . I can also reproduce this problem using:

(for idx in `seq 1 100` ; do echo x ; done) | ./a.out 

vs:

(for idx in `seq 1 100` ; do echo x ; done) | js tryp.js 

This also works:

python -c 'print "x\n" * 100,' | js tryp.js

Regards,

-- Shlomi Fish

[shlomif]

Hi @kripken ,

what this perl code does is emit 100 lines containing "x" (and a newline) followed by and "end-of-stream". print emits output to the string, and "x" is the repeat operator - http://perl-begin.org/tutorials/perl-for-newbies/part1/#page--arrays--x--PAGE . I can also reproduce this problem using:

(for idx in `seq 1 100` ; do echo x ; done) | ./a.out 

vs:

(for idx in `seq 1 100` ; do echo x ; done) | js tryp.js 

This also works:

python -c 'print "x\n" * 100,' | js tryp.js

Regards,

-- Shlomi Fish

[kripken]

I'm not sure what's going wrong here. But it must be something to do with how js engines handle pipes I guess. In general, only node (the only one not relevant here) has good support for console stuff like pipes, because people use it for that kind of stuff, other js shells are mainly just used for testing.

[shlomif]

@kripken : I see. So what can we do and what should we do?

[kripken]

Best thing would be to figure out how to properly read from standard input
in node, because that is the one that should be able to do that.

On Tue, May 21, 2013 at 2:14 PM, Shlomi Fish notifications@github.comwrote:

@krpiken : I see. So what can we do and what should we do?

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/1151#issuecomment-18241387
.

[shlomif]

@kripken : I see regarding Node. I'll try to investigate.