max_threads not working as expected

[bogdandubyk]

What happened?

max_threads is not working as expected, or I do not understand how does it supose to work. For now I'm using franken in non-worker mode, recenlty updated to 1.22.4, in caddy config I have

      frankenphp {
        num_threads 45
        max_threads 45
      }

running

 curl -s http://localhost:2019/config/ | python3 -m json.tool | grep -A5 -i "thread\|frankenphp"                                                                                                                           
          "frankenphp": {                                                                                                                                                                                                               
              "max_threads": 45,                                                                                                                                                                                                        
              "num_threads": 45                                                                                                                                                                                                         
          },                                                                                                                                                                                                                            
          "http": {                                                                                                                                                                                                                     
              "http_port": 8080,                                                                                                                                                                                                        
              "metrics": {},                                                                                                                                                                                                            
              "servers": {  

shows that confing is there, but Prometheus metrics for frankenphp_busy_threads are showing more than 150 threads sometimes, but frankenphp_total_threads is straight line on 45 as expected. Why it's not limiting number of threads

Build Type

Docker (Alpine)

Worker Mode

No

Operating System

GNU/Linux

CPU Architecture

x86_64

PHP configuration

phpinfo() output

HP Version => 8.5.7

System => Linux products-data-api-f749b4879-xppkk 6.12.83-115.161.amzn2023.x86_64 #1 SMP PREEMPT_DYNAMIC Thu May 14 12:25:55 UTC 2026 x86_64
Build Date => Jun  5 2026 01:16:10
Build System => Linux - Docker
Build Provider => https://github.com/docker-library/php
Configure Command =>  './configure'  '--build=x86_64-linux-musl' '--sysconfdir=/usr/local/etc' '--with-config-file-path=/usr/local/etc/php' '--with-config-file-scan-dir=/usr/local/etc/php/conf.d' '--enable-option-checking=fatal' '--with-mhash' '--with-pic' '--enable-mbstring' '--enable-mysqlnd' '--with-password-argon2' '--with-sodium=shared' '--with-pdo-sqlite=/usr' '--with-sqlite3=/usr' '--with-curl' '--with-iconv=/usr' '--with-openssl' '--with-readline' '--with-zlib' '--enable-phpdbg' '--enable-phpdbg-readline' '--with-pear' '--enable-embed' '--enable-zts' '--disable-zend-signals' 'build_alias=x86_64-linux-musl' 'PHP_UNAME=Linux - Docker' 'PHP_BUILD_PROVIDER=https://github.com/docker-library/php'
Server API => Command Line Interface
Virtual Directory Support => enabled
Configuration File (php.ini) Path => /usr/local/etc/php
Loaded Configuration File => /usr/local/etc/php/php.ini
Scan this dir for additional .ini files => /usr/local/etc/php/conf.d
Additional .ini files parsed => /usr/local/etc/php/conf.d/docker-php-ext-apcu.ini,
/usr/local/etc/php/conf.d/docker-php-ext-blackfire.ini,
/usr/local/etc/php/conf.d/docker-php-ext-intl.ini,
/usr/local/etc/php/conf.d/docker-php-ext-mongodb.ini,
/usr/local/etc/php/conf.d/docker-php-ext-pcntl.ini,
/usr/local/etc/php/conf.d/docker-php-ext-pdo_pgsql.ini,
/usr/local/etc/php/conf.d/docker-php-ext-pgsql.ini,
/usr/local/etc/php/conf.d/docker-php-ext-redis.ini,
/usr/local/etc/php/conf.d/docker-php-ext-sodium.ini,
/usr/local/etc/php/conf.d/docker-php-ext-zip.ini,
/usr/local/etc/php/conf.d/z-apcu.ini,
/usr/local/etc/php/conf.d/z-custom.ini

PHP API => 20250925
PHP Extension => 20250925
Zend Extension => 420250925
Zend Extension Build => API420250925,TS
PHP Extension Build => API20250925,TS
PHP Integer Size => 64 bits
Debug Build => no
Thread Safety => enabled
Thread API => POSIX Threads
Zend Signal Handling => disabled
Zend Memory Manager => enabled
Zend Multibyte Support => provided by mbstring
Zend Max Execution Timers => enabled
IPv6 Support => enabled
DTrace Support => disabled

Registered PHP Streams => https, ftps, compress.zlib, php, file, glob, data, http, ftp, phar, zip
Registered Stream Socket Transports => tcp, udp, unix, udg, ssl, tls, tlsv1.0, tlsv1.1, tlsv1.2, tlsv1.3
Registered Stream Filters => zlib.*, convert.iconv.*, string.rot13, string.toupper, string.tolower, convert.*, consumed, dechunk

This program makes use of the Zend Scripting Language Engine:
Zend Engine v4.5.7, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.7, Copyright (c), by Zend Technologies


 _______________________________________________________________________


Configuration

apcu

APCu Support => Disabled
Version => 5.1.28
APCu Debugging => Disabled
MMAP Support => Enabled
MMAP File Mask =>  
Serialization Support => Disabled
Build Date => Jun  8 2026 14:08:22

Directive => Local Value => Master Value
apc.coredump_unmap => Off => Off
apc.enable_cli => Off => Off
apc.enabled => Off => Off
apc.entries_hint => 0 => 0
apc.gc_ttl => 3600 => 3600
apc.mmap_file_mask => no value => no value
apc.mmap_hugepage_size => 0 => 0
apc.preload_path => no value => no value
apc.serializer => php => php
apc.shm_size => 1M => 1M
apc.slam_defense => Off => Off
apc.smart => 0 => 0
apc.ttl => 1800 => 1800
apc.use_request_time => Off => Off

Core

PHP Version => 8.5.7

Directive => Local Value => Master Value
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allow_url_include => Off => Off
arg_separator.input => & => &
arg_separator.output => & => &
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auto_globals_jit => On => On
auto_prepend_file => no value => no value
browscap => no value => no value
default_charset => UTF-8 => UTF-8
default_mimetype => text/html => text/html
disable_functions => no value => no value
display_errors => Off => Off
display_startup_errors => Off => Off
doc_root => no value => no value
docref_ext => no value => no value
docref_root => no value => no value
enable_dl => Off => Off
enable_post_data_reading => On => On
error_append_string => no value => no value
error_log => no value => no value
error_log_mode => 0644 => 0644
error_prepend_string => no value => no value
error_reporting => 22527 => 22527
expose_php => On => On
extension_dir => /usr/local/lib/php/extensions/no-debug-zts-20250925 => /usr/local/lib/php/extensions/no-debug-zts-20250925
fatal_error_backtraces => On => On
fiber.stack_size => no value => no value
file_uploads => On => On
hard_timeout => 2 => 2
highlight.comment => <span style="color: #FF8000">#FF8000</span> => <span style="color: #FF8000">#FF8000</span>
highlight.default => <span style="color: #0000BB">#0000BB</span> => <span style="color: #0000BB">#0000BB</span>
highlight.html => <span style="color: #000000">#000000</span> => <span style="color: #000000">#000000</span>
highlight.keyword => <span style="color: #007700">#007700</span> => <span style="color: #007700">#007700</span>
highlight.string => <span style="color: #DD0000">#DD0000</span> => <span style="color: #DD0000">#DD0000</span>
html_errors => Off => Off
ignore_repeated_errors => Off => Off
ignore_repeated_source => Off => Off
ignore_user_abort => Off => Off
implicit_flush => On => On
include_path => .:/usr/local/lib/php => .:/usr/local/lib/php
input_encoding => no value => no value
internal_encoding => no value => no value
log_errors => On => On
mail.add_x_header => Off => Off
mail.cr_lf_mode => crlf => crlf
mail.force_extra_parameters => no value => no value
mail.log => no value => no value
mail.mixed_lf_and_crlf => Off => Off
max_execution_time => 0 => 0
max_file_uploads => 20 => 20
max_input_nesting_level => 64 => 64
max_input_time => -1 => -1
max_input_vars => 1000 => 1000
max_memory_limit => -1 => -1
max_multipart_body_parts => -1 => -1
memory_limit => 1280M => 1280M
open_basedir => no value => no value
output_buffering => 0 => 0
output_encoding => no value => no value
output_handler => no value => no value
post_max_size => 82M => 82M
precision => 14 => 14
realpath_cache_size => 4096K => 4096K
realpath_cache_ttl => 600 => 600
register_argc_argv => Off => Off
report_memleaks => On => On
report_zend_debug => Off => Off
request_order => GP => GP
sendmail_from => no value => no value
sendmail_path => /usr/sbin/sendmail -t -i => /usr/sbin/sendmail -t -i
serialize_precision => -1 => -1
short_open_tag => Off => Off
SMTP => localhost => localhost
smtp_port => 25 => 25
sys_temp_dir => no value => no value
syslog.facility => LOG_USER => LOG_USER
syslog.filter => no-ctrl => no-ctrl
syslog.ident => php => php
unserialize_callback_func => no value => no value
upload_max_filesize => 82M => 82M
upload_tmp_dir => no value => no value
user_dir => no value => no value
user_ini.cache_ttl => 300 => 300
user_ini.filename => .user.ini => .user.ini
variables_order => GPCS => GPCS
xmlrpc_error_number => 0 => 0
xmlrpc_errors => Off => Off
zend.assertions => -1 => -1
zend.detect_unicode => On => On
zend.enable_gc => On => On
zend.exception_ignore_args => On => On
zend.exception_string_param_max_len => 0 => 0
zend.max_allowed_stack_size => 0 => 0
zend.multibyte => Off => Off
zend.reserved_stack_size => 0 => 0
zend.script_encoding => no value => no value

ctype

ctype functions => enabled

curl

cURL support => enabled
cURL Information => 8.19.0
Age => 11
Features
AsynchDNS => Yes
CharConv => No
Debug => No
GSS-Negotiate => No
IDN => Yes
IPv6 => Yes
krb4 => No
Largefile => Yes
libz => Yes
NTLM => Yes
NTLMWB => No
SPNEGO => No
SSL => Yes
SSPI => No
TLS-SRP => Yes
HTTP2 => Yes
GSSAPI => No
KERBEROS5 => No
UNIX_SOCKETS => Yes
PSL => Yes
HTTPS_PROXY => Yes
MULTI_SSL => No
BROTLI => Yes
ALTSVC => Yes
HTTP3 => No
UNICODE => No
ZSTD => Yes
HSTS => Yes
GSASL => No
Protocols => dict, file, ftp, ftps, gopher, gophers, http, https, imap, imaps, mqtt, mqtts, pop3, pop3s, rtsp, smb, smbs, smtp, smtps, telnet, tftp, ws, wss
Host => x86_64-alpine-linux-musl
SSL Version => OpenSSL/3.5.6
ZLib Version => 1.3.2

Directive => Local Value => Master Value
curl.cainfo => no value => no value

date

date/time support => enabled
timelib version => 2022.15
"Olson" Timezone Database Version => 2026.1
Timezone Database => internal
Default timezone => UTC

Directive => Local Value => Master Value
date.default_latitude => 31.7667 => 31.7667
date.default_longitude => 35.2333 => 35.2333
date.sunrise_zenith => 90.833333 => 90.833333
date.sunset_zenith => 90.833333 => 90.833333
date.timezone => UTC => UTC

dom

DOM/XML => enabled
DOM/XML API Version => 20031129
libxml Version => 2.13.9
HTML Support => enabled
XPath Support => enabled
XPointer Support => enabled
Schema Support => enabled
RelaxNG Support => enabled

fileinfo

fileinfo support => enabled
libmagic => 5.46

filter

Input Validation and Filtering => enabled

Directive => Local Value => Master Value
filter.default => unsafe_raw => unsafe_raw
filter.default_flags => no value => no value

hash

hash support => enabled
Hashing Engines => md2 md4 md5 sha1 sha224 sha256 sha384 sha512/224 sha512/256 sha512 sha3-224 sha3-256 sha3-384 sha3-512 ripemd128 ripemd160 ripemd256 ripemd320 whirlpool tiger128,3 tiger160,3 tiger192,3 tiger128,4 tiger160,4 tiger192,4 snefru snefru256 gost gost-crypto adler32 crc32 crc32b crc32c fnv132 fnv1a32 fnv164 fnv1a64 joaat murmur3a murmur3c murmur3f xxh32 xxh64 xxh3 xxh128 haval128,3 haval160,3 haval192,3 haval224,3 haval256,3 haval128,4 haval160,4 haval192,4 haval224,4 haval256,4 haval128,5 haval160,5 haval192,5 haval224,5 haval256,5 

MHASH support => Enabled
MHASH API Version => Emulated Support

iconv

iconv support => enabled
iconv implementation => libiconv
iconv library version => 1.18

Directive => Local Value => Master Value
iconv.input_encoding => no value => no value
iconv.internal_encoding => no value => no value
iconv.output_encoding => no value => no value

intl

Internationalization support => enabled
ICU version => 76.1
ICU Data version => 76.1
ICU TZData version => 2024b
ICU Unicode version => 16.0

Directive => Local Value => Master Value
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intl.error_level => 0 => 0
intl.use_exceptions => Off => Off

json

json support => enabled

lexbor

Lexbor support => active
Lexbor version => 2.7.0

libxml

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libXML Compiled Version => 2.13.9
libXML Loaded Version => 21309
libXML streams => enabled

mbstring

Multibyte Support => enabled
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HTTP input encoding translation => disabled
libmbfl version => 1.3.2

mbstring extension makes use of "streamable kanji code filter and converter", which is distributed under the GNU Lesser General Public License version 2.1.

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mbstring.internal_encoding => no value => no value
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mbstring.regex_stack_limit => 100000 => 100000
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mbstring.substitute_character => no value => no value

mongodb

MongoDB support => enabled
MongoDB extension version => 2.3.3
MongoDB extension stability => stable
libbson bundled version => 2.3.0
libmongoc bundled version => 2.3.0
libmongoc SSL => enabled
libmongoc SSL library => OpenSSL
libmongoc crypto => enabled
libmongoc crypto library => libcrypto
libmongoc crypto system profile => disabled
libmongoc SASL => disabled
libmongoc SRV => enabled
libmongoc compression => enabled
libmongoc compression snappy => disabled
libmongoc compression zlib => enabled
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libmongocrypt bundled version => 1.17.3
libmongocrypt crypto => enabled
libmongocrypt crypto library => libcrypto
crypt_shared library version => unknown

Directive => Local Value => Master Value
mongodb.debug => no value => no value

mysqlnd

mysqlnd => enabled
Version => mysqlnd 8.5.7
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core SSL => supported
extended SSL => supported
Command buffer size => 4096
Read buffer size => 32768
Read timeout => 86400
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Collecting memory statistics => No
Tracing => n/a
Loaded plugins => mysqlnd,debug_trace,auth_plugin_mysql_native_password,auth_plugin_mysql_clear_password,auth_plugin_caching_sha2_password,auth_plugin_sha256_password
API Extensions =>  

openssl

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OpenSSL Header Version => OpenSSL 3.5.6 7 Apr 2026
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Directive => Local Value => Master Value
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openssl.capath => no value => no value
openssl.libctx => custom => custom

pcntl

pcntl support => enabled

pcre

PCRE (Perl Compatible Regular Expressions) Support => enabled
PCRE Library Version => 10.44 2024-06-07
PCRE Unicode Version => 15.0.0
PCRE JIT Support => enabled
PCRE JIT Target => x86 64bit (little endian + unaligned)

Directive => Local Value => Master Value
pcre.backtrack_limit => 1000000 => 1000000
pcre.jit => On => On
pcre.recursion_limit => 100000 => 100000

PDO

PDO support => enabled
PDO drivers => sqlite, pgsql

pdo_pgsql

PDO Driver for PostgreSQL => enabled
PostgreSQL(libpq) Version => 18.4

pdo_sqlite

PDO Driver for SQLite 3.x => enabled
SQLite Library => 3.51.2

pgsql

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PostgreSQL (libpq) Version => 18.4
Multibyte character support => enabled
Active Persistent Links => 0
Active Links => 0

Directive => Local Value => Master Value
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pgsql.max_persistent => Unlimited => Unlimited

Phar

Phar: PHP Archive support => enabled
Phar API version => 1.1.1
Phar-based phar archives => enabled
Tar-based phar archives => enabled
ZIP-based phar archives => enabled
gzip compression => enabled
bzip2 compression => disabled (install ext/bz2)
Native OpenSSL support => enabled


Phar based on pear/PHP_Archive, original concept by Davey Shafik.
Phar fully realized by Gregory Beaver and Marcus Boerger.
Portions of tar implementation Copyright (c) 2003-2009 Tim Kientzle.
Directive => Local Value => Master Value
phar.cache_list => no value => no value
phar.readonly => On => On
phar.require_hash => On => On

posix

POSIX support => enabled

random

Version => 8.5.7

readline

Readline Support => enabled
Readline library => 8.3

Directive => Local Value => Master Value
cli.pager => no value => no value
cli.prompt => \b \>  => \b \> 

redis

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Redis Version => 6.3.0
Redis Sentinel Version => 1.0
Available serializers => php, json

Directive => Local Value => Master Value
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redis.arrays.auth => no value => no value
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redis.arrays.connecttimeout => 0 => 0
redis.arrays.consistent => 0 => 0
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redis.session.lock_retries => 100 => 100
redis.session.lock_wait_time => 20000 => 20000
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Reflection

Reflection => enabled

session

Session Support => enabled
Registered save handlers => files user redis rediscluster 
Registered serializer handlers => php_serialize php php_binary 

Directive => Local Value => Master Value
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session.cache_expire => 180 => 180
session.cache_limiter => nocache => nocache
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session.cookie_httponly => Off => Off
session.cookie_lifetime => 0 => 0
session.cookie_partitioned => Off => Off
session.cookie_path => / => /
session.cookie_samesite => no value => no value
session.cookie_secure => Off => Off
session.gc_divisor => 1000 => 1000
session.gc_maxlifetime => 1440 => 1440
session.gc_probability => 1 => 1
session.lazy_write => On => On
session.name => PHPSESSID => PHPSESSID
session.referer_check => no value => no value
session.save_handler => no value => no value
session.save_path => no value => no value
session.serialize_handler => no value => no value
session.sid_bits_per_character => 4 => 4
session.sid_length => 32 => 32
session.upload_progress.cleanup => On => On
session.upload_progress.enabled => On => On
session.upload_progress.freq => 1% => 1%
session.upload_progress.min_freq => 1 => 1
session.upload_progress.name => PHP_SESSION_UPLOAD_PROGRESS => PHP_SESSION_UPLOAD_PROGRESS
session.upload_progress.prefix => upload_progress_ => upload_progress_
session.use_cookies => On => On
session.use_only_cookies => On => On
session.use_strict_mode => Off => Off
session.use_trans_sid => Off => Off

SimpleXML

SimpleXML support => enabled
Schema support => enabled

sodium

sodium support => enabled
libsodium headers version => 1.0.20
libsodium library version => 1.0.20

SPL

SPL support => enabled
Interfaces => OuterIterator, RecursiveIterator, SeekableIterator, SplObserver, SplSubject
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sqlite3

SQLite3 support => enabled
SQLite Library => 3.51.2

Directive => Local Value => Master Value
sqlite3.defensive => On => On
sqlite3.extension_dir => no value => no value

standard

Dynamic Library Support => enabled
Path to sendmail => /usr/sbin/sendmail -t -i

Directive => Local Value => Master Value
assert.active => On => On
assert.bail => Off => Off
assert.callback => no value => no value
assert.exception => On => On
assert.warning => On => On
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default_socket_timeout => 60 => 60
from => no value => no value
session.trans_sid_hosts => no value => no value
session.trans_sid_tags => a=href,area=href,frame=src,form= => a=href,area=href,frame=src,form=
unserialize_max_depth => 4096 => 4096
url_rewriter.hosts => no value => no value
url_rewriter.tags => form= => form=
user_agent => no value => no value

tokenizer

Tokenizer Support => enabled

uri

URI support => active
uriparser bundled version => 1.0.2

xml

XML Support => active
XML Namespace Support => active
libxml2 Version => 2.13.9

xmlreader

XMLReader => enabled

xmlwriter

XMLWriter => enabled

Zend OPcache

Opcode Caching => Up and Running
Optimization => Enabled
SHM Cache => Enabled
File Cache => Disabled
JIT => Disabled
Startup => OK
Shared memory model => mmap
Cache hits => 0
Cache misses => 0
Used memory => 68766976
Free memory => 199668480
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opcache.file_cache => no value => no value
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opcache.jit_blacklist_side_trace => 8 => 8
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opcache.jit_debug => 0 => 0
opcache.jit_hot_func => 127 => 127
opcache.jit_hot_loop => 61 => 61
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opcache.jit_max_root_traces => 1024 => 1024
opcache.jit_max_side_traces => 128 => 128
opcache.jit_max_trace_length => 1024 => 1024
opcache.jit_prof_threshold => 0.005 => 0.005
opcache.lockfile_path => /tmp => /tmp
opcache.log_verbosity_level => 1 => 1
opcache.max_accelerated_files => 32531 => 32531
opcache.max_file_size => 0 => 0
opcache.max_wasted_percentage => 5 => 5
opcache.memory_consumption => 256 => 256
opcache.opt_debug_level => 0 => 0
opcache.optimization_level => 0x7FFEBFFF => 0x7FFEBFFF
opcache.preferred_memory_model => no value => no value
opcache.preload => /srv/app/config/preload.php => /srv/app/config/preload.php
opcache.preload_user => daemon => daemon
opcache.protect_memory => Off => Off
opcache.record_warnings => Off => Off
opcache.restrict_api => no value => no value
opcache.revalidate_freq => 0 => 0
opcache.revalidate_path => Off => Off
opcache.save_comments => On => On
opcache.use_cwd => On => On
opcache.validate_permission => Off => Off
opcache.validate_root => Off => Off
opcache.validate_timestamps => Off => Off

zip

Zip => enabled
Zip version => 1.22.8
Libzip version => 1.11.4
BZIP2 compression => Yes
XZ compression => Yes
ZSTD compression => Yes
AES-128 encryption => Yes
AES-192 encryption => Yes
AES-256 encryption => Yes

zlib

ZLib Support => enabled
Stream Wrapper => compress.zlib://
Stream Filter => zlib.inflate, zlib.deflate
Compiled Version => 1.3.2
Linked Version => 1.3.2

Directive => Local Value => Master Value
zlib.output_compression => Off => Off
zlib.output_compression_level => -1 => -1
zlib.output_handler => no value => no value

Relevant log output

Relevant log output

[AlliBalliBaba]

After looking through the code I think this metric is a bit badly named. frankenphp_busy_threads includes queued requests. So the actual number of threads currently handling a request would be:

frankenphp_busy_threads - frankenphp_queue_depth

Not sure what the original intention was, but I agree that this should be mentioned in the docs or maybe even be renamed.