TypeError: Cannot read property 'on' of undefined

[ohardy]

I use onchange package which crash in tree-kill. Stack trace:

<folder>/node_modules/tree-kill/index.js:78
    ps.stdout.on('data', function (data) {
             ^

TypeError: Cannot read property 'on' of undefined
    at buildProcessTree (/***/node_modules/tree-kill/index.js:78:14)
    at /***/node_modules/tree-kill/index.js:99:11
    at Array.forEach (native)
    at ChildProcess.onClose (/***/node_modules/tree-kill/index.js:94:31)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:192:7)
    at maybeClose (internal/child_process.js:890:16)
    at Socket.<anonymous> (internal/child_process.js:334:11)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:189:7)

[billiegoose]

If I understand correctly, you are using the onchange package and it is using tree-kill? I don't yet have enough information to figure out what went wrong. The error Cannot read property 'on' of undefined would imply that ps.stdout is undefined, but I have never seen that happen before. Could you add some more details like what: operating system, Node version?

[ohardy]

I hope it will help you

Node version: 7.5.0

I added some debug and added a test to not call ps.stdout.on if ps.stdout is null and that's it:

onchange: change to src/server.js
onchange: killing command 41413 and restarting
kill(41413, 'SIGTERM');
pgrep -P 41413
pgrep -P 1
pgrep -P 61
pgrep -P 62

toggle full log entire log

pgrep -P 64
pgrep -P 65
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pgrep -P 34658

pgrep -P 34661
pgrep -P 34668
pgrep -P 35612
Null stdout for : spawnChildProcessesList(35612)
pgrep -P 35636
Null stdout for : spawnChildProcessesList(35636)
pgrep -P 35641
Null stdout for : spawnChildProcessesList(35641)
pgrep -P 35669
Null stdout for : spawnChildProcessesList(35669)
pgrep -P 35714
Null stdout for : spawnChildProcessesList(35714)
pgrep -P 36565
Null stdout for : spawnChildProcessesList(36565)
pgrep -P 36566
Null stdout for : spawnChildProcessesList(36566)
pgrep -P 36567
Null stdout for : spawnChildProcessesList(36567)
pgrep -P 36731
Null stdout for : spawnChildProcessesList(36731)
pgrep -P 36732
Null stdout for : spawnChildProcessesList(36732)
pgrep -P 36733
Null stdout for : spawnChildProcessesList(36733)
pgrep -P 36734
Null stdout for : spawnChildProcessesList(36734)
pgrep -P 36738
Null stdout for : spawnChildProcessesList(36738)
pgrep -P 36739
Null stdout for : spawnChildProcessesList(36739)
pgrep -P 36740
Null stdout for : spawnChildProcessesList(36740)
pgrep -P 36741
Null stdout for : spawnChildProcessesList(36741)
pgrep -P 37001
Null stdout for : spawnChildProcessesList(37001)
pgrep -P 37002
Null stdout for : spawnChildProcessesList(37002)
pgrep -P 37004
Null stdout for : spawnChildProcessesList(37004)
pgrep -P 37006
Null stdout for : spawnChildProcessesList(37006)
pgrep -P 37026
Null stdout for : spawnChildProcessesList(37026)
pgrep -P 40026
Null stdout for : spawnChildProcessesList(40026)
pgrep -P 41303
Null stdout for : spawnChildProcessesList(41303)
pgrep -P 41412
Null stdout for : spawnChildProcessesList(41412)
pgrep -P 41413
Null stdout for : spawnChildProcessesList(41413)
pgrep -P 41424
Null stdout for : spawnChildProcessesList(41424)
events.js:161
      throw er; // Unhandled 'error' event
      ^

Error: spawn pgrep EAGAIN
    at exports._errnoException (util.js:1023:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
    at onErrorNT (internal/child_process.js:359:16)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)

killAll(tree, signal, callback);

is never called

[Marak]

What happens if you switch back to Node version 6?

[ohardy]

Same bug with v6.9.5

[billiegoose]

Huh. This is on Linux?

[ohardy]

Mac OS 10.12.3

[ohardy]

So i try to fix the issue. I thinks it's a too many process problem for the buildProcessTree part, if i add a setTimeout for each spawn call, no more stdout null bug.

But the other problem is :

kill :  75531 SIGTERM
onClose pid : 75531 code: 0
Object.keys(pidsToProcess).length :  0

So in onClose, i change:

if (code != 0) {

to:

if (code == 0) {

And everything works.

Why do you check the return code of the process ?

[ickma]

I met the same issue as u @ohardy , your solution saved me!

[billiegoose]

Why do you check the return code of the process ?

The return code of pgrep -P tells us whether the process has children that also need to be killed. From the manpage:

EXIT STATUS
       0      One or more processes matched the criteria.
       1      No processes matched.
       2      Syntax error in the command line.
       3      Fatal error: out of memory etc.

By changing the != to == you're bailing out of the recursion prematurely. However the more I study this code, the more I'm not sure it is right. I think the forEach loop and the callback cb invocation creates a race condition. I think this code should probably be refactored to make the control flow simpler, but I don't have the time right now. Long story short @ohardy and @ickma, somehow the process you're trying to kill creates so many children that tree-kill runs into a race condition. The fix suggested will probably keep tree-kill from crashing and never calling killAll, but it might allow children/grandchildren of the process to escape it's killer grasp and become zombies.

If anyone thinks of a better way to do the recursive process killing I'm all ears. I don't have spare cycles to investigate. (And don't have a Mac.) @ickma is yours Mac OSX too?

[DPiaz]

In my case, i removed the option {stdio: 'inherit'} from the call spawn(command, args, options) and works.

[mogutan88]

In my case, I have proctools installed on my macOS at, /usr/local/bin. I confirmed that the output of '/usr/local/bin/pgrep -P' and that of '/usr/bin/pgrep -P' are different. So, uninstalling the proctools, changing the PATH, or even changing the tree-kill/index.js code like below, solved the problem.

    case 'darwin':
        buildProcessTree(pid, tree, pidsToProcess, function (parentPid) {
          return spawn('/usr/bin/pgrep', ['-P', parentPid]);