Unable to create thread

hello, everyone

i am using sip message dialplan and written that dialpan in /etc/asterisk/extensions_custom.conf
dialplan is:

[astsms]
exten => _X.,1,NoOp(SMS receiving dialplan invoked)
exten => _X.,n,NoOp(To ${MESSAGE(to)})
exten => _X.,n,NoOp(From ${MESSAGE(from)})
exten => _X.,n,NoOp(Body ${MESSAGE(body)})
exten => _X.,n,Set(ACTUALTO=${CUT(MESSAGE(to),@,1)})
exten => _X.,n,ExecIf($[“${ACTUALTO}” != “sip:${EXTEN}”]?Set(ACTUALTO=sip:${EXTEN}))
exten => _X.,n,MessageSend(${ACTUALTO},${MESSAGE(from)})
;exten => _X.,n,Set(FILE(/var/spool/asterisk/sms/${STRFTIME(${EPOCH},%F-%T)}-${CALLERID(num)}-${EXTEN}.txt,a)=${MESSAGE(body)})
exten => _X.,n,NoOp(Send status is ${MESSAGE_SEND_STATUS})
exten => _X.,n,GotoIf($[“${MESSAGE_SEND_STATUS}” != “SUCCESS”]?sendfailedmsg)
exten => _X.,n,Hangup()
;
; Handle failed messaging
exten => _X.,n(sendfailedmsg),NoOp(Sending error to user)
exten => _X.,n,Set(SRC=${MESSAGE(from)})
exten => _X.,n,Set(DST=${MESSAGE(to)})
exten => _X.,n,Set(MSG=${MESSAGE(body)})
exten => _X.,n,Set(MESSAGE(body)=“[${STRFTIME(${EPOCH},%d%m%Y-%H:%M:%S)}] Your message to ${EXTEN} has failed. Sending when available”)
exten => _X.,n,Set(ME_1=${CUT(MESSAGE(from),<,2)})
exten => _X.,n,Set(ACTUALFROM=${CUT(ME_1,@,1)})
exten => _X.,n,MessageSend(${ACTUALFROM},ServiceCenter)
exten => _X.,n,GotoIf($[“${INQUEUE}” != “1”]?startq)
exten => _X.,n,Hangup()
;
exten => _X.,n(startq),NoOp(Queueing messaging for offline)
exten => _X.,n,Set(MSGTIME=${STRFTIME(${EPOCH},%d%m%Y-%H:%M:%S)})
;exten => _X.,n,System(/bin/bash /var/lib/asterisk/agi-bin/sc.sh)
exten => _X.,n,System(/bin/bash /var/lib/asterisk/agi-bin/astqueue.sh -s ‘${SRC}’ -d ‘${DST}’ -m ‘${MSG}’)
exten => _X.,n,Hangup()
[app-fakeanswer]
exten => _X.,1,NoCDR
exten => _X.,n,Set(DESTDEV=${EXTEN})
exten => _X.,n,Set(THISDEVSTATE=${DEVICE_STATE(SIP/${DESTDEV})})
exten => _X.,n,GotoIf($[“${THISDEVSTATE}” = “UNAVAILABLE”]?hang)
exten => _X.,n,GotoIf($[“${THISDEVSTATE}” = “UNKNOWN”]?hang)
exten => _X.,n,GotoIf($[“${THISDEVSTATE}” = “LAGGED”]?hang)
exten => _X.,n,Answer
exten => _X.,n,Hangup()
exten => _X.,n(hang),Hangup()

i got this issue when send more than 200 message simultaneously from single to single user.

[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[58989] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58973] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58969] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58978] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58889] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58991] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58966] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58985] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58995] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58895] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58906] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[8086] pbx_spool.c: Unable to create thread (returned error: 11)
[2019-01-08 07:05:02] WARNING[58899] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58976] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58984] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58993] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] WARNING[58970] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59026] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59029] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59029] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59018] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59018] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59019] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59019] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59006] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59006] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59032] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59032] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59011] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59011] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59020] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59020] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59028] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59028] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)
[2019-01-08 07:05:02] WARNING[59015] pbx.c: Failed to create new channel thread
[2019-01-08 07:05:02] NOTICE[59015] pbx_spool.c: Call failed to go through, reason (0) Call Failure (not BUSY, and not NO_ANSWER, maybe Circuit busy or down?)

i have 200 users on this server. when more than 200 message request send within a second than cpu utilization is 100% and load average of server is around 50. at this stage asterisk stopped and server hanged up.
sometime dialplan missed the message request.

server: intel i5 with 4 core
RAM: 8GB
harddrive: 1TB

i dont know to handle the message request through dialpan and need help to resolve this problem.
please help me.