Configuring Actor Applications¶
CAF configures applications at startup using an actor_system_config
or a
user-defined subclass of that type. The config objects allow users to add custom
types, to load modules (optional components), and to fine-tune the behavior of
loaded modules with command line options or configuration files (see
Command Line Options and INI Configuration Files).
The following code example is a minimal CAF application with a Middleman but without any custom configuration options.
void caf_main(actor_system& system) {
// ...
}
CAF_MAIN(io::middleman)
The compiler expands this example code to the following.
void caf_main(actor_system& system) {
// ...
}
int main(int argc, char** argv) {
return exec_main<io::middleman>(caf_main, argc, argv);
}
The function exec_main
performs several steps:
- Initialize all meta objects for the type ID blocks listed in
CAF_MAIN
. - Create a config object. If
caf_main
has two arguments, then CAF assumes that the second argument is the configuration and the type gets derived from that argument. Otherwise, CAF usesactor_system_config
. - Parse command line arguments and configuration file (if present).
- Load all modules requested in
CAF_MAIN
. - Create an actor system.
- Call
caf_main
with the actor system and optionally withconfig
.
When implementing the steps performed by CAF_MAIN
by hand, the main
function would resemble the following (pseudo) code:
int main(int argc, char** argv) {
// Create the config.
actor_system_config cfg;
// Add runtime-type information for user-defined types.
cfg.add_message_types<...>();
// Read CLI options.
if (auto err = cfg.parse(argc, argv)) {
std::cerr << "error while parsing CLI and file options: "
<< to_string(err) << std::endl;
return EXIT_FAILURE;
}
// Return immediately if a help text was printed.
if (cfg.cli_helptext_printed)
return EXIT_SUCCESS;
// Load modules.
cfg.load<...>();
// Create the actor system.
actor_system sys{cfg};
// Run user-defined code.
caf_main(sys, cfg);
return EXIT_SUCCESS;
}
Using CAF_MAIN
simply automates that boilerplate code. A minimal example
with a custom type ID block as well as a custom configuration class with the I/O
module loaded looks as follows:
CAF_BEGIN_TYPE_ID_BLOCK(my, first_custom_type_id)
// ...
CAF_END_TYPE_ID_BLOCK(my)
class my_config : public actor_system_config {
public:
my_config() {
// ...
}
};
void caf_main(actor_system& system, const my_config& cfg) {
// ...
}
CAF_MAIN(id_block::my, io::middleman)
Note
Using type ID blocks is optional. Users can also call add_message_type
for each user-defined type in the constructor of my_config
.
Loading Modules¶
The simplest way to load modules is to use the macro CAF_MAIN
and
to pass a list of all requested modules, as shown below.
void caf_main(actor_system& system) {
// ...
}
CAF_MAIN(mod1, mod2, ...)
Alternatively, users can load modules in user-defined config classes.
class my_config : public actor_system_config {
public:
my_config() {
load<mod1>();
load<mod2>();
// ...
}
};
The third option is to simply call x.load<mod1>()
on a config
object before initializing an actor system with it.
Command Line Options and INI Configuration Files¶
CAF organizes program options in categories and parses CLI arguments as well as
INI files. CLI arguments override values in the INI file which override
hard-coded defaults. Users can add any number of custom program options by
implementing a subtype of actor_system_config
. The example below
adds three options to the global
category.
class config : public actor_system_config {
public:
uint16_t port = 0;
std::string host = "localhost";
bool server_mode = false;
config() {
opt_group{custom_options_, "global"}
.add(port, "port,p", "set port")
.add(host, "host,H", "set host (ignored in server mode)")
.add(server_mode, "server-mode,s", "enable server mode");
}
};
We create a new global
category in custom_options_
.
Each following call to add
then appends individual options to the
category. The first argument to add
is the associated variable. The
second argument is the name for the parameter, optionally suffixed with a
comma-separated single-character short name. The short name is only considered
for CLI parsing and allows users to abbreviate commonly used option names. The
third and final argument to add
is a help text.
The custom config
class allows end users to set the port for the application
to 42 with either -p 42
(short name) or --port=42
(long name). The long
option name is prefixed by the category when using a different category than
global
. For example, adding the port option to the category foo
means
end users have to type --foo.port=42
when using the long name. Short names
are unaffected by the category, but have to be unique.
Boolean options do not require arguments. The member variable
server_mode
is set to true
if the command line contains
either --server-mode
or -s
.
The example uses member variables for capturing user-provided settings for
simplicity. However, this is not required. For example,
add<bool>(...)
allows omitting the first argument entirely. All
values of the configuration are accessible with get_or
. Note that
all global options can omit the "global."
prefix.
CAF adds the program options help
(with short names -h
and -?
) as well as long-help
to the global
category.
The default name for the INI file is caf-application.ini
. Users can
change the file name and path by passing --config-file=<path>
on the
command line.
INI files are organized in categories. No value is allowed outside of a category
(no implicit global
category). The parses uses the following syntax:
Syntax | Type |
---|---|
key=true |
Boolean |
key=1 |
Integer |
key=1.0 |
Floating point number |
key=1ms |
Timespan |
key='foo' |
Atom |
key="foo" |
String |
key=[0, 1, ...] |
List |
key={a=1, b=2, ...} |
Dictionary (map) |
The following example INI file lists all standard options in CAF and their
default value. Note that some options such as scheduler.max-threads
are usually detected at runtime and thus have no hard-coded default.
; This file shows all possible parameters with defaults.
; Values enclosed in <> are detected at runtime unless defined by the user.
; when using the default scheduler
[scheduler]
; accepted alternative: 'sharing'
policy='stealing'
; configures whether the scheduler generates profiling output
enable-profiling=false
; forces a fixed number of threads if set
max-threads=<number of cores>
; maximum number of messages actors can consume in one run
max-throughput=<infinite>
; measurement resolution in milliseconds (only if profiling is enabled)
profiling-resolution=100ms
; output file for profiler data (only if profiling is enabled)
profiling-output-file="/dev/null"
; when using 'stealing' as scheduler policy
[work-stealing]
; number of zero-sleep-interval polling attempts
aggressive-poll-attempts=100
; frequency of steal attempts during aggressive polling
aggressive-steal-interval=10
; number of moderately aggressive polling attempts
moderate-poll-attempts=500
; frequency of steal attempts during moderate polling
moderate-steal-interval=5
; sleep interval between poll attempts
moderate-sleep-duration=50us
; frequency of steal attempts during relaxed polling
relaxed-steal-interval=1
; sleep interval between poll attempts
relaxed-sleep-duration=10ms
; when loading io::middleman
[middleman]
; configures whether MMs try to span a full mesh
enable-automatic-connections=false
; application identifier of this node, prevents connection to other CAF
; instances with different identifier
app-identifier=""
; maximum number of consecutive I/O reads per broker
max-consecutive-reads=50
; heartbeat message interval in ms (0 disables heartbeating)
heartbeat-interval=0ms
; configures whether the MM attaches its internal utility actors to the
; scheduler instead of dedicating individual threads (needed only for
; deterministic testing)
attach-utility-actors=false
; configures whether the MM starts a background thread for I/O activity,
; setting this to true allows fully deterministic execution in unit test and
; requires the user to trigger I/O manually
manual-multiplexing=false
; disables communication via TCP
disable-tcp=false
; enable communication via UDP
enable-udp=false
; configures how many background workers are spawned for deserialization,
; by default CAF uses 1-4 workers depending on the number of cores
workers=<min(3, number of cores / 4) + 1>
; when compiling with logging enabled
[logger]
; file name template for output log file files (empty string disables logging)
file-name="actor_log_[PID]_[TIMESTAMP]_[NODE].log"
; format for rendering individual log file entries
file-format="%r %c %p %a %t %C %M %F:%L %m%n"
; configures the minimum severity of messages that are written to the log file
; (quiet|error|warning|info|debug|trace)
file-verbosity='trace'
; mode for console log output generation (none|colored|uncolored)
console='none'
; format for printing individual log entries to the console
console-format="%m"
; configures the minimum severity of messages that are written to the console
; (quiet|error|warning|info|debug|trace)
console-verbosity='trace'
; excludes listed components from logging (list of atoms)
component-blacklist=[]
Adding Custom Message Types¶
CAF requires serialization support for all of its message types (see Type Inspection). In addition, CAF also needs a mapping of unique type names to user-defined types at runtime. This is required to deserialize arbitrary messages from the network.
The function actor_system_config::add_message_type
adds runtime-type
information for a single type. It takes a template parameter (the message type)
and one function argument (the type name). For example,
cfg.add_message_type<foo>("foo")
would add runtime-type information for the
type foo
. However, calling add_message_type
for each type individually
is both verbose and prone to error.
For new code, we strongly recommend using the new type ID blocks. When setting
the CMake option CAF_ENABLE_TYPE_ID_CHECKS
to ON
(or calling the
configure
script with --enable-type-id-checks
), CAF raises a static
assertion that prohibits any message type that does not appear in such a type ID
block. When using this API, users can instead call add_message_types
once
per message block. Combined with the type ID checks, this makes sure that the
runtime-type information never runs out of sync when adding new message types.
Passing the type ID blocks to CAF_MAIN
also automates the setup steps for
adding new message types.
A type ID block in CAF starts by calling CAF_BEGIN_TYPE_ID_BLOCK
. Inside the
block appear any number of CAF_ADD_TYPE_ID
and CAF_ADD_ATOM
statements.
The type ID block only requires forward declarations. The block ends at
CAF_END_TYPE_ID_BLOCK
, as shown in the example below.
struct foo;
struct foo2;
CAF_BEGIN_TYPE_ID_BLOCK(custom_types_1, first_custom_type_id)
CAF_ADD_TYPE_ID(custom_types_1, (foo))
CAF_ADD_TYPE_ID(custom_types_1, (foo2))
CAF_ADD_TYPE_ID(custom_types_1, (std::pair<int32_t, int32_t>) )
CAF_END_TYPE_ID_BLOCK(custom_types_1)
Note
The second argument to CAF_ADD_TYPE_ID
(the type) must appear in extra
parentheses. This unusual syntax is an artifact of argument handling in
macros. Without the extra set of parentheses, we would not be able to add
types with commas such as std::pair
.
The first argument to all macros is the name of the type ID block. The macro
expands a name X
to caf::id_block::X
. In the example above, we can refer
to the custom type ID block with caf::id_block::custom_types_1
. To add the
required runtime-type information to CAF, we can either call
cfg.add_message_types<caf::id_block::custom_types_1>()
on a config object
pass the ID block to CAF_MAIN
:
CAF_MAIN(caf::id_block::custom_types_1)
Note
At the point of calling CAF_MAIN
or add_message_types
, the compiler
must have the type declaration plus all inspect
overloads available for
each type in the type ID block.
Adding Custom Actor Types experimental¶
Adding actor types to the configuration allows users to spawn actors by their
name. In particular, this enables spawning of actors on a different node (see
Remote Spawning of Actors experimental). For our example configuration, we consider the following
simple calculator
actor.
using calculator = caf::typed_actor<
caf::replies_to<caf::add_atom, int32_t, int32_t>::with<int32_t>,
caf::replies_to<caf::sub_atom, int32_t, int32_t>::with<int32_t>>;
Adding the calculator actor type to our config is achieved by calling
add_actor_type
. After calling this in our config, we can spawn the
calculator
anywhere in the distributed actor system (assuming all nodes use
the same config). Note that the handle type still requires a type ID (see
Adding Custom Message Types).
After adding the actor type to the config, we can spawn our calculator
by
name. Unlike the regular spawn
overloads, this version requires wrapping the
constructor arguments into a message
and the function might fail and thus
returns an expected
:
if (auto x = system.spawn<calculator>("calculator", make_message())) {
// ... do something with *x ...
} else {
std::cerr << "*** unable to spawn a calculator: " << to_string(x.error())
<< std::endl;
// ...
}
Adding dynamically typed actors to the config is achieved in the same way. When
spawning a dynamically typed actor in this way, the template parameter is
simply actor
. For example, spawning an actor “foo” which requires
one string is created with:
auto worker = system.spawn<actor>("foo", make_message("bar"));
Because constructor (or function) arguments for spawning the actor are stored in
a message
, only actors with appropriate input types are allowed. Pointer
types, for example, are illegal in messages.
Log Output¶
CAF comes with a logger integrated into the actor system. By default, CAF itself
won’t emit any log messages. Developers can set the verbosity of CAF itself at
build time by setting the CMake option CAF_LOG_LEVEL
manually or by passing
--with-log-level=...
to the configure
script. The available verbosity
levels are (from least to most output):
error
warning
info
debug
trace
The logging infrastructure is always available to users, regardless of the verbosity level of CAF itself.
File Name¶
The output file is generated from the template configured by
logger-file-name
. This template supports the following variables.
Variable | Output |
---|---|
[PID] |
The OS-specific process ID. |
[TIMESTAMP] |
The UNIX timestamp on startup. |
[NODE] |
The node ID of the CAF system. |
Console¶
Console output is disabled per default. Setting logger-console
to either
uncolored
or colored
prints log events to std::clog
. Using the
colored
option will print the log events in different colors depending on
the severity level.
Format Strings¶
CAF uses log4j-like format strings for configuring printing of individual
events via logger-file-format
and
logger-console-format
. Note that format modifiers are not supported
at the moment. The recognized field identifiers are:
Pattern | Output |
---|---|
%c |
The category/component. |
%C |
The full qualifier of the current function. For example, the function void ns::foo::bar() would print ns.foo . |
%d |
The date in ISO 8601 format, i.e., "YYYY-MM-DDThh:mm:ss" . |
%F |
The file name. |
%L |
The line number. |
%m |
The user-defined log message. |
%M |
The name of the current function. For example, the name of void ns::foo::bar() is printed as bar . |
%n |
A newline. |
%p |
The priority (severity level). |
%r |
Elapsed time since starting the application in milliseconds. |
%t |
ID of the current thread. |
%a |
ID of the current actor (or actor0 when not logging inside an actor). |
%% |
A single percent sign. |
Filtering¶
The two configuration options logger.component-blacklist
and
logger.(file|console)-verbosity
reduce the amount of generated log events.
The former is a list of excluded component names and the latter can increase the
reported severity level (but not decrease it beyond the level defined at compile
time).