Namespaces
namespace	fd_limit_impl

Classes
struct	FdLimitOutcome
	The result of acting on a plan. More...

struct	FdLimitPlan

struct	FdLimits

struct	SocketOptions

struct	WireHeader

Enumerations
enum class	Comp : uint8_t { None = 0 , Snappy = 1 }

Functions
const std::string &	clock_domain_id ()
	Stable identifier for the clock this process reads. Computed once (function-local static, thread-safe init) and cached for the life of the process.

uint64_t	agent_capacity (uint64_t soft)
	How many agents a given soft limit leaves room for.

FdLimits	query_fd_limits ()
	Reads the limits currently in force, with `hard` clamped as described above.

std::string	describe_fd_limits (const FdLimits &limits)
	Renders e.g. "1024 soft / 1048576 hard, about 492 agents".

std::string	fd_limit_hint ()
	The hint appended to every message that reports a limit worth raising.

FdLimitPlan	plan_fd_limit (std::optional< int64_t > requested, const FdLimits &limits)

FdLimitOutcome	apply_fd_limit (const FdLimitPlan &plan)

bool	is_fd_exhaustion (int err)

mongocxx::instance &	mongo_instance ()
	Return the process-wide mongocxx driver instance.

uint64_t	fnv1a64 (const void *data, size_t len)

std::string	digest_hex (std::string_view bytes)

std::filesystem::path	attachment_cache_root ()

void	sweep_stale (const std::filesystem::path &agent_dir, std::string_view keep_digest, const std::string &name, const std::string &ext)

std::filesystem::path	store_attachment (const std::string &name, const std::string &ext, const std::string &bytes)
	Persist a broker-served attachment under its content digest and return the path to load it from.

template<typename T >
std::optional< T >	resolve_setting (toml::node_view< toml::node > fleet_cfg, toml::node_view< toml::node > agent_cfg, std::string_view key)

std::string	make_wire_header (WireFormat fmt, Comp comp, bool has_blob)

bool	parse_wire_header (const std::string &part, WireHeader &out)

Comp	resolve_compression (Compression policy, size_t size)

std::string	encode_payload (const nlohmann::json &j, WireFormat fmt)

bool	decode_to_json_text (const std::string &raw, uint8_t format, uint8_t comp, std::string &json_text_out)

Variables
constexpr uint64_t	FD_PER_AGENT = 2

constexpr uint64_t	FD_BROKER_OVERHEAD = 64

constexpr uint64_t	FD_LOW_WATERMARK = 1024

constexpr uint64_t	FD_ABSOLUTE_CEILING = 1048576

constexpr char	WIRE_MAGIC [4] = {'M', 'A', 'D', 'S'}

constexpr uint8_t	WIRE_HDR_VERSION = 1

constexpr uint8_t	WIRE_FLAG_BLOB = 0x01

constexpr size_t	WIRE_HEADER_SIZE

Enumeration Type Documentation

◆ Comp

enum class Mads::detail::Comp : uint8_t

strong

Enumerator
None
Snappy

Definition at line 46 of file wire_format.hpp.

Function Documentation

◆ agent_capacity()

uint64_t Mads::detail::agent_capacity ( uint64_t soft )

inline

How many agents a given soft limit leaves room for.

Definition at line 76 of file fd_limit.hpp.

References FD_BROKER_OVERHEAD, and FD_PER_AGENT.

Referenced by describe_fd_limits(), and plan_fd_limit().

◆ apply_fd_limit()

FdLimitOutcome Mads::detail::apply_fd_limit ( const FdLimitPlan & plan )

inline

Carries out plan. Only ever moves the soft limit: rlim_max is left untouched, since raising it needs CAP_SYS_RESOURCE and would simply fail for an unprivileged broker, while moving the soft limit anywhere at or below the hard one never needs privileges at all – in either direction.

Lowering does not close descriptors that are already open; it only makes further allocations fail. Since the broker applies this before binding anything, that distinction does not arise in practice.

Definition at line 318 of file fd_limit.hpp.

References Mads::detail::FdLimitPlan::action, Mads::detail::FdLimitOutcome::applied, Mads::detail::FdLimitOutcome::error, Mads::detail::FdLimitOutcome::limits, Mads::detail::FdLimitPlan::Lower, query_fd_limits(), Mads::detail::FdLimitPlan::Raise, Mads::detail::FdLimits::supported, and Mads::detail::FdLimitPlan::target.

◆ attachment_cache_root()

std::filesystem::path Mads::detail::attachment_cache_root ( )

inline

Definition at line 86 of file plugin_cache.hpp.

Referenced by store_attachment().

◆ clock_domain_id()

const std::string & Mads::detail::clock_domain_id ( )

inline

Stable identifier for the clock this process reads. Computed once (function-local static, thread-safe init) and cached for the life of the process.

Definition at line 45 of file clock_domain.hpp.

References HOST_NAME_MAX.

◆ decode_to_json_text()

bool Mads::detail::decode_to_json_text	(	const std::string &	raw,
		uint8_t	format,
		uint8_t	comp,
		std::string &	json_text_out
	)

inline

Definition at line 115 of file wire_format.hpp.

References Snappy.

◆ describe_fd_limits()

std::string Mads::detail::describe_fd_limits ( const FdLimits & limits )

inline

Renders e.g. "1024 soft / 1048576 hard, about 492 agents".

Definition at line 187 of file fd_limit.hpp.

References agent_capacity(), Mads::detail::FdLimits::hard, and Mads::detail::FdLimits::soft.

Referenced by plan_fd_limit().

◆ digest_hex()

std::string Mads::detail::digest_hex ( std::string_view bytes )

inline

Definition at line 74 of file plugin_cache.hpp.

References fnv1a64().

Referenced by store_attachment().

◆ encode_payload()

std::string Mads::detail::encode_payload	(	const nlohmann::json &	j,
		WireFormat	fmt
	)

inline

Definition at line 104 of file wire_format.hpp.

◆ fd_limit_hint()

std::string Mads::detail::fd_limit_hint ( )

inline

The hint appended to every message that reports a limit worth raising.

Definition at line 194 of file fd_limit.hpp.

Referenced by plan_fd_limit().

◆ fnv1a64()

uint64_t Mads::detail::fnv1a64	(	const void *	data,
		size_t	len
	)

inline

Definition at line 62 of file plugin_cache.hpp.

Referenced by digest_hex().

◆ is_fd_exhaustion()

bool Mads::detail::is_fd_exhaustion ( int err )

inline

True when err is the errno of a process (or system) descriptor table that has filled up – the condition every explanatory message here exists for.

Definition at line 346 of file fd_limit.hpp.

◆ make_wire_header()

std::string Mads::detail::make_wire_header	(	WireFormat	fmt,
		Comp	comp,
		bool	has_blob
	)

inline

Definition at line 56 of file wire_format.hpp.

References WIRE_FLAG_BLOB, WIRE_HDR_VERSION, WIRE_HEADER_SIZE, and WIRE_MAGIC.

◆ mongo_instance()

mongocxx::instance & Mads::detail::mongo_instance ( )

inline

Return the process-wide mongocxx driver instance.

mongocxx::instance must be constructed exactly once per process and must outlive every other driver object; constructing a second one while the first is alive throws mongocxx::logic_error{k_cannot_recreate_instance}. Holding one as a class member therefore makes it impossible for two driver-using MADS objects to coexist, so every translation unit that touches the driver shares the single function-local static created here.

The static is destroyed at process exit, after all clients built on top of it.

Note: This is inline, so all callers linked into the same binary share one static. MadsCore is a single shared library, so that holds for MADS.

Definition at line 36 of file mongo_instance.hpp.

◆ parse_wire_header()

bool Mads::detail::parse_wire_header	(	const std::string &	part,
		WireHeader &	out
	)

inline

Definition at line 73 of file wire_format.hpp.

References Mads::detail::WireHeader::compression, Mads::detail::WireHeader::format, Mads::detail::WireHeader::has_blob, Mads::detail::WireHeader::hdr_version, Mads::detail::WireHeader::schema, WIRE_FLAG_BLOB, WIRE_HEADER_SIZE, and WIRE_MAGIC.

◆ plan_fd_limit()

FdLimitPlan Mads::detail::plan_fd_limit	(	std::optional< int64_t >	requested,
		const FdLimits &	limits
	)

inline

Decides what to do. requested is the resolved max_open_files value: nullopt leaves the limit untouched, 0 means "as high as this process is allowed to go", and a positive value is a specific soft limit.

Definition at line 202 of file fd_limit.hpp.

◆ query_fd_limits()

FdLimits Mads::detail::query_fd_limits ( )

inline

Reads the limits currently in force, with hard clamped as described above.

Definition at line 132 of file fd_limit.hpp.

References FD_ABSOLUTE_CEILING, Mads::detail::FdLimits::hard, Mads::detail::fd_limit_impl::kernel_fd_ceiling(), Mads::detail::FdLimits::soft, and Mads::detail::FdLimits::supported.

Referenced by apply_fd_limit().

◆ resolve_compression()

Comp Mads::detail::resolve_compression	(	Compression	policy,
		size_t	size
	)

inline

Definition at line 91 of file wire_format.hpp.

References None, and Snappy.

◆ resolve_setting()

template<typename T >

std::optional< T > Mads::detail::resolve_setting	(	toml::node_view< toml::node >	fleet_cfg,
		toml::node_view< toml::node >	agent_cfg,
		std::string_view	key
	)

Definition at line 24 of file socket_options.hpp.

◆ store_attachment()

std::filesystem::path Mads::detail::store_attachment	(	const std::string &	name,
		const std::string &	ext,
		const std::string &	bytes
	)

inline

Persist a broker-served attachment under its content digest and return the path to load it from.

Safe to call concurrently from any number of processes and threads: the bytes at the returned path are never mutated in place, so a copy another process has already dlopen()'d stays exactly as that process mapped it.

Parameters

name	Settings section name; also the returned file's stem.
ext	Extension without the leading dot (e.g. "plugin").
bytes	The attachment as received from the broker.

Returns: Absolute path to the cached file.

Exceptions

std::runtime_error if the attachment cannot be persisted.

Definition at line 134 of file plugin_cache.hpp.

References attachment_cache_root(), digest_hex(), and sweep_stale().

◆ sweep_stale()

void Mads::detail::sweep_stale	(	const std::filesystem::path &	agent_dir,
		std::string_view	keep_digest,
		const std::string &	name,
		const std::string &	ext
	)

inline

Definition at line 96 of file plugin_cache.hpp.

Referenced by store_attachment().

Variable Documentation

◆ FD_ABSOLUTE_CEILING

constexpr uint64_t Mads::detail::FD_ABSOLUTE_CEILING = 1048576

inlineconstexpr

Last-resort ceiling when the OS reports an unbounded hard limit and no kernel cap could be read. Matches Linux's own default fs.nr_open.

Definition at line 73 of file fd_limit.hpp.

Referenced by query_fd_limits().

◆ FD_BROKER_OVERHEAD

constexpr uint64_t Mads::detail::FD_BROKER_OVERHEAD = 64

inlineconstexpr

The broker's own descriptor footprint, independent of fleet size: three listening sockets, ~10 libzmq socket mailboxes, the context reaper's and each I/O thread's poller, stdio, and the settings-file watch.

Platform-dependent, because the mailboxes dominate it and their cost is not the same everywhere: libzmq's signaler uses eventfd() where it exists (Linux), costing one descriptor per mailbox, and falls back to a socketpair – two descriptors – everywhere else. Measured at idle: ~34 on Linux, 49 on macOS. Rounded up in both cases, so the capacity estimate errs toward understating how many agents will fit rather than overstating.

Definition at line 63 of file fd_limit.hpp.

Referenced by agent_capacity(), and plan_fd_limit().

◆ FD_LOW_WATERMARK

constexpr uint64_t Mads::detail::FD_LOW_WATERMARK = 1024

inlineconstexpr

Soft limit at or below which raising is worth suggesting – the default on essentially every Linux distribution, and the value systemd hands a unit that does not set LimitNOFILE=.

Definition at line 69 of file fd_limit.hpp.

Referenced by plan_fd_limit().

◆ FD_PER_AGENT

constexpr uint64_t Mads::detail::FD_PER_AGENT = 2

inlineconstexpr

Descriptors a single connected agent costs the broker for as long as it stays connected: one for its publisher, one for its subscriber. (The settings request needs a third, but only while it is in flight.)

Definition at line 48 of file fd_limit.hpp.

Referenced by agent_capacity().

◆ WIRE_FLAG_BLOB

constexpr uint8_t Mads::detail::WIRE_FLAG_BLOB = 0x01

constexpr

Definition at line 41 of file wire_format.hpp.

Referenced by make_wire_header(), and parse_wire_header().

◆ WIRE_HDR_VERSION

constexpr uint8_t Mads::detail::WIRE_HDR_VERSION = 1

constexpr

Definition at line 40 of file wire_format.hpp.

Referenced by make_wire_header().

◆ WIRE_HEADER_SIZE

constexpr size_t Mads::detail::WIRE_HEADER_SIZE

constexpr

Initial value:

= 4  + 1  + 1  +
                                    1  + 1  +
                                    4

Definition at line 42 of file wire_format.hpp.

Referenced by make_wire_header(), and parse_wire_header().

◆ WIRE_MAGIC

constexpr char Mads::detail::WIRE_MAGIC[4] = {'M', 'A', 'D', 'S'}

constexpr

Definition at line 39 of file wire_format.hpp.

Referenced by make_wire_header(), and parse_wire_header().

Namespaces

Classes

Enumerations

Functions

Variables

Enumeration Type Documentation

◆ Comp

Function Documentation

◆ agent_capacity()

◆ apply_fd_limit()

◆ attachment_cache_root()

◆ clock_domain_id()

◆ decode_to_json_text()

◆ describe_fd_limits()

◆ digest_hex()

◆ encode_payload()

◆ fd_limit_hint()

◆ fnv1a64()

◆ is_fd_exhaustion()

◆ make_wire_header()

◆ mongo_instance()

◆ parse_wire_header()

◆ plan_fd_limit()

◆ query_fd_limits()

◆ resolve_compression()

◆ resolve_setting()

◆ store_attachment()

◆ sweep_stale()

Variable Documentation

◆ FD_ABSOLUTE_CEILING

◆ FD_BROKER_OVERHEAD

◆ FD_LOW_WATERMARK

◆ FD_PER_AGENT

◆ WIRE_FLAG_BLOB

◆ WIRE_HDR_VERSION

◆ WIRE_HEADER_SIZE

◆ WIRE_MAGIC