Introduction

Ev is a static class providing access to the default loop and to some common operations.

Class synopsis

Predefined Constants

Flags passed to create a loop:

Ev::FLAG_AUTO

The default flags value

Ev::FLAG_NOENV

If this flag used(or the program runs setuid or setgid), libev won't look at the environment variable LIBEV_FLAGS . Otherwise(by default), LIBEV_FLAGS will override the flags completely if it is found. Useful for performance tests and searching for bugs.

Ev::FLAG_FORKCHECK

Makes libev check for a fork in each iteration, instead of calling EvLoop::fork manually. This works by calling getpid() on every iteration of the loop, and thus this might slow down the event loop with lots of loop iterations, but usually is not noticeable. This flag setting cannot be overridden or specified in the LIBEV_FLAGS environment variable.

Ev::FLAG_NOINOTIFY

When this flag is specified, libev won't attempt to use the inotify API for its » ev_stat watchers. The flag can be useful to conserve inotify file descriptors, as otherwise each loop using ev_stat watchers consumes one inotify handle.

Ev::FLAG_SIGNALFD

When this flag is specified, libev will attempt to use the signalfd API for its » ev_signal (and » ev_child ) watchers. This API delivers signals synchronously, which makes it both faster and might make it possible to get the queued signal data. It can also simplify signal handling with threads, as long as signals are properly blocked in threads. Signalfd will not be used by default.

Ev::FLAG_NOSIGMASK

When this flag is specified, libev will avoid to modify the signal mask. Specifically, this means having to make sure signals are unblocked before receiving them.

This behaviour is useful for custom signal handling, or handling signals only in specific threads.

Flags passed to Ev::run , or EvLoop::run

Ev::RUN_NOWAIT

Means that event loop will look for new events, will handle those events and any already outstanding ones, but will not wait and block the process in case there are no events and will return after one iteration of the loop. This is sometimes useful to poll and handle new events while doing lengthy calculations, to keep the program responsive.

Ev::RUN_ONCE

Means that event loop will look for new events (waiting if necessary) and will handle those and any already outstanding ones. It will block the process until at least one new event arrives (which could be an event internal to libev itself, so there is no guarantee that a user-registered callback will be called), and will return after one iteration of the loop.

Flags passed to Ev::stop , or EvLoop::stop

Ev::BREAK_CANCEL

Cancel the break operation.

Ev::BREAK_ONE

Makes the innermost Ev::run (or EvLoop::run ) call return.

Ev::BREAK_ALL

Makes all nested Ev::run (or EvLoop::run ) calls return.

Watcher priorities:

Ev::MINPRI

Minimum allowed watcher priority.

Ev::MAXPRI

Maximum allowed watcher priority.

Bit masks of (received) events:

Ev::READ

The file descriptor in the EvIo watcher has become readable.

Ev::WRITE

The file descriptor in the EvIo watcher has become writable.

Ev::TIMER

EvTimer watcher has been timed out.

Ev::PERIODIC

EvPeriodic watcher has been timed out.

Ev::SIGNAL

A signal specified in EvSignal::__construct has been received.

Ev::CHILD

The pid specified in EvChild::__construct has received a status change.

Ev::STAT

The path specified in EvStat watcher changed its attributes.

Ev::IDLE

EvIdle watcher works when there is nothing to do with other watchers.

Ev::PREPARE

All EvPrepare watchers are invoked just before Ev::run starts. Thus, EvPrepare watchers are the last watchers invoked before the event loop sleeps or polls for new events.

Ev::CHECK

All EvCheck watchers are queued just after Ev::run has gathered the new events, but before it queues any callbacks for any received events. Thus, EvCheck watchers will be invoked before any other watchers of the same or lower priority within an event loop iteration.

Ev::EMBED

The embedded event loop specified in the EvEmbed watcher needs attention.

Ev::CUSTOM

Not ever sent(or otherwise used) by libev itself, but can be freely used by libev users to signal watchers (e.g. via EvWatcher::feed ).

Ev::ERROR

An unspecified error has occurred, the watcher has been stopped. This might happen because the watcher could not be properly started because libev ran out of memory, a file descriptor was found to be closed or any other problem. Libev considers these application bugs. See also » ANATOMY OF A WATCHER

Backend flags:

Ev::BACKEND_SELECT

select(2) backend

Ev::BACKEND_POLL

poll(2) backend

Ev::BACKEND_EPOLL

Linux-specific epoll(7) backend for both pre- and post-2.6.9 kernels

Ev::BACKEND_KQUEUE

kqueue backend used on most BSD systems. EvEmbed watcher could be used to embed one loop(with kqueue backend) into another. For instance, one can try to create an event loop with kqueue backend and use it for sockets only.

Ev::BACKEND_DEVPOLL

Solaris 8 backend. This is not implemented yet.

Ev::BACKEND_PORT

Solaris 10 event port mechanism with a good scaling.

Ev::BACKEND_ALL

Try all backends(even currupted ones). It's not recommended to use it explicitly. Bitwise operators should be applied here(e.g. Ev::BACKEND_ALL & ~ Ev::BACKEND_KQUEUE ) Use Ev::recommendedBackends , or don't specify any backends at all.

Ev::BACKEND_MASK

Not a backend, but a mask to select all backend bits from flags value to mask out any backends(e.g. when modifying the LIBEV_FLAGS environment variable).

Note:

For the default loop during module initialization phase Ev registers » ev_loop_fork call by means of pthread_atfork (if available).

Note:

There are methods providing access to the default event loop in Ev class(e.g. Ev::iteration , Ev::depth etc.) For custom loops (created with EvLoop::__construct ) these values may be accessed via corresponding properties and methods of the EvLoop class.

The instance of the default event loop itself can be fetched by means of EvLoop::defaultLoop method.

Introduction

EvPrepare and EvCheck watchers are usually used in pairs. EvPrepare watchers get invoked before the process blocks, EvCheck afterwards.

It is not allowed to call EvLoop::run or similar methods or functions that enter the current event loop from either EvPrepare or EvCheck watchers. Other loops than the current one are fine, however. The rationale behind this is that one don't need to check for recursion in those watchers, i.e. the sequence will always be: EvPrepare -> blocking -> EvCheck , so having a watcher of each kind they will always be called in pairs bracketing the blocking call.

The main purpose is to integrate other event mechanisms into libev and their use is somewhat advanced. They could be used, for example, to track variable changes, implement custom watchers, integrate net-snmp or a coroutine library and lots more. They are also occasionally useful to cache some data and want to flush it before blocking.

It is recommended to give EvCheck watchers highest( Ev::MAXPRI ) priority, to ensure that they are being run before any other watchers after the poll (this doesn’t matter for EvPrepare watchers).

Also, EvCheck watchers should not activate/feed events. While libev fully supports this, they might get executed before other EvCheck watchers did their job.

Class synopsis

Introduction

EvChild watchers trigger when the process receives a SIGCHLD in response to some child status changes (most typically when a child dies or exits). It is permissible to install an EvChild watcher after the child has been forked(which implies it might have already exited), as long as the event loop isn't entered(or is continued from a watcher), i.e. forking and then immediately registering a watcher for the child is fine, but forking and registering a watcher a few event loop iterations later or in the next callback invocation is not.

It is allowed to register EvChild watchers in the default loop only.

Class synopsis

Properties

pid

Readonly . The process ID this watcher watches out for, or 0 , meaning any process ID.

rpid

Readonly .The process ID that detected a status change.

rstatus

Readonly . The process exit status caused by rpid .

Introduction

Used to embed one event loop into another.

Class synopsis

Properties

is_active

data

is_pending

priority

embed

Introduction

Fork watchers are called when a fork() was detected (usually because whoever signalled libev about it by calling EvLoop::fork ). The invocation is done before the event loop blocks next and before EvCheck watchers are being called, and only in the child after the fork. Note, that if whoever calling EvLoop::fork calls it in the wrong process, the fork handlers will be invoked, too.

Class synopsis

Introduction

EvIdle watchers trigger events when no other events of the same or higher priority are pending ( EvPrepare , EvCheck and other EvIdle watchers do not count as receiving events ).

Thus, as long as the process is busy handling sockets or timeouts(or even signals) of the same or higher priority it will not be triggered. But when the process is in idle(or only lower-priority watchers are pending), the EvIdle watchers are being called once per event loop iteration - until stopped, that is, or the process receives more events and becomes busy again with higher priority stuff.

Apart from keeping the process non-blocking(which is a useful on its own sometimes), EvIdle watchers are a good place to do "pseudo-background processing" , or delay processing stuff to after the event loop has handled all outstanding events.

The most noticeable effect is that as long as any idle watchers are active, the process will not block when waiting for new events.

Class synopsis

Introduction

EvIo watchers check whether a file descriptor(or socket, or a stream castable to numeric file descriptor) is readable or writable in each iteration of the event loop, or, more precisely, when reading would not block the process and writing would at least be able to write some data. This behaviour is called level-triggering because events are kept receiving as long as the condition persists. To stop receiving events just stop the watcher.

The number of read and/or write event watchers per fd is unlimited. Setting all file descriptors to non-blocking mode is also usually a good idea(but not required).

Another thing to watch out for is that it is quite easy to receive false readiness notifications, i.e. the callback might be called with Ev::READ but a subsequent read() will actually block because there is no data. It is very easy to get into this situation. Thus it is best to always use non-blocking I/O: An extra read() returning EAGAIN (or similar) is far preferable to a program hanging until some data arrives.

If for some reason it is impossible to run the fd in non-blocking mode, then separately re-test whether a file descriptor is really ready. Some people additionally use SIGALRM and an interval timer, just to be sure thry won't block infinitely.

Always consider using non-blocking mode.

Class synopsis

Properties

fd

events

Introduction

Represents an event loop that is always distinct from the default loop . Unlike the default loop , it cannot handle EvChild watchers.

Having threads we have to create a loop per thread, and use the default loop in the parent thread.

The default event loop is initialized automatically by Ev . It is accessible via methods of the Ev class, or via EvLoop::defaultLoop method.

Class synopsis

Properties

data

Custom data attached to loop

backend

Readonly . The backend flags indicating the event backend in use.

is_default_loop

Readonly . TRUE if it is the default event loop.

iteration

The current iteration count of the loop. See Ev::iteration

pending

The number of pending watchers. 0 indicates that there are no watchers pending.

io_interval

Higher io_interval allows libev to spend more time collecting EvIo events, so more events can be handled per iteration, at the cost of increasing latency. Timeouts (both EvPeriodic and EvTimer ) will not be affected. Setting this to a non-zero value will introduce an additional sleep() call into most loop iterations. The sleep time ensures that libev will not poll for EvIo events more often than once per this interval, on average. Many programs can usually benefit by setting the io_interval to a value near 0.1 , which is often enough for interactive servers(not for games). It usually doesn't make much sense to set it to a lower value than 0.01 , as this approaches the timing granularity of most systems.

See also » FUNCTIONS CONTROLLING EVENT LOOPS .

timeout_interval

Higher timeout_interval allows libev to spend more time collecting timeouts, at the expense of increased latency/jitter/inexactness(the watcher callback will be called later). EvIo watchers will not be affected. Setting this to a non-null value will not introduce any overhead in libev . See also » FUNCTIONS CONTROLLING EVENT LOOPS .

depth

The recursion depth. See Ev::depth .

Introduction

Periodic watchers are also timers of a kind, but they are very versatile.

Unlike EvTimer , EvPeriodic watchers are not based on real time(or relative time, the physical time that passes) but on wall clock time(absolute time, calendar or clock). The difference is that wall clock time can run faster or slower than real time, and time jumps are not uncommon(e.g. when adjusting it).

EvPeriodic watcher can be configured to trigger after some specific point in time. For example, if an EvPeriodic watcher is configured to trigger "in 10 seconds" (e.g. EvLoop::now + 10.0 , i.e. an absolute time, not a delay), and the system clock is reset to January of the previous year , then it will take a year or more to trigger the event (unlike an EvTimer , which would still trigger roughly 10 seconds after starting it as it uses a relative timeout).

As with timers, the callback is guaranteed to be invoked only when the point in time where it is supposed to trigger has passed. If multiple timers become ready during the same loop iteration then the ones with earlier time-out values are invoked before ones with later time-out values (but this is no longer true when a callback calls EvLoop::run recursively).

Class synopsis

Properties

offset

When repeating, this contains the offset value, otherwise this is the absolute point in time(the offset value passed to EvPeriodic::set , although libev might modify this value for better numerical stability).

interval

The current interval value. Can be modified any time, but changes only take effect when the periodic timer fires or EvPeriodic::again is being called.

Introduction

EvPrepare and EvCheck watchers are usually used in pairs. EvPrepare watchers get invoked before the process blocks, EvCheck afterwards.

It is not allowed to call EvLoop::run or similar methods or functions that enter the current event loop from either EvPrepare or EvCheck watchers. Other loops than the current one are fine, however. The rationale behind this is that one don't need to check for recursion in those watchers, i.e. the sequence will always be: EvPrepare -> blocking -> EvCheck , so having a watcher of each kind they will always be called in pairs bracketing the blocking call.

The main purpose is to integrate other event mechanisms into libev and their use is somewhat advanced. They could be used, for example, to track variable changes, implement custom watchers, integrate net-snmp or a coroutine library and lots more. They are also occasionally useful to cache some data and want to flush it before blocking.

It is recommended to give EvCheck watchers highest( Ev::MAXPRI ) priority, to ensure that they are being run before any other watchers after the poll (this doesn’t matter for EvPrepare watchers).

Also, EvCheck watchers should not activate/feed events. While libev fully supports this, they might get executed before other EvCheck watchers did their job.

Class synopsis

Introduction

EvSignal watchers will trigger an event when the process receives a specific signal one or more times. Even though signals are very asynchronous, libev will try its best to deliver signals synchronously, i.e. as part of the normal event processing, like any other event.

There is no limit for the number of watchers for the same signal, but only within the same loop, i.e. one can watch for SIGINT in the default loop and for SIGIO in another loop, but it is not allowed to watch for SIGINT in both the default loop and another loop at the same time. At the moment, SIGCHLD is permanently tied to the default loop.

If possible and supported, libev will install its handlers with SA_RESTART (or equivalent) behaviour enabled, so system calls should not be unduly interrupted. In case of a problem with system calls getting interrupted by signals, all the signals can be blocked in an EvCheck watcher and unblocked in a EvPrepare watcher.

Class synopsis

Properties

signum

Signal number. See the constants exported by pcntl extension. See also signal(7) man page.

Introduction

EvStat monitors a file system path for attribute changes. It calls stat() on that path in regular intervals(or when the OS signals it changed) and sees if it changed compared to the last time, invoking the callback if it did.

The path does not need to exist: changing from "path exists" to "path does not exist" is a status change like any other. The condition "path does not exist" is signified by the 'nlink' item being 0(returned by EvStat::attr method).

The path must not end in a slash or contain special components such as '.' or .. . The path should be absolute: if it is relative and the working directory changes, then the behaviour is undefined.

Since there is no portable change notification interface available, the portable implementation simply calls stat() regularly on the path to see if it changed somehow. For this case a recommended polling interval can be specified. If one specifies a polling interval of 0.0 (highly recommended) then a suitable, unspecified default value will be used(which could be expected to be around 5 seconds, although this might change dynamically). libev will also impose a minimum interval which is currently around 0.1 , but that’s usually overkill.

This watcher type is not meant for massive numbers of EvStat watchers, as even with OS-supported change notifications, this can be resource-intensive.

Class synopsis

Properties

interval

Readonly . Hint on how quickly a change is expected to be detected and should normally be specified as 0.0 to let libev choose a suitable value.

path

Readonly . The path to wait for status changes on.

Introduction

EvTimer watchers are simple relative timers that generate an event after a given time, and optionally repeating in regular intervals after that.

The timers are based on real time, that is, if one registers an event that times out after an hour and resets the system clock to January last year , it will still time out after(roughly) one hour. "Roughly" because detecting time jumps is hard, and some inaccuracies are unavoidable.

The callback is guaranteed to be invoked only after its timeout has passed (not at, so on systems with very low-resolution clocks this might introduce a small delay). If multiple timers become ready during the same loop iteration then the ones with earlier time-out values are invoked before ones of the same priority with later time-out values (but this is no longer true when a callback calls EvLoop::run recursively).

The timer itself will do a best-effort at avoiding drift, that is, if a timer is configured to trigger every 10 seconds, then it will normally trigger at exactly 10 second intervals. If, however, the script cannot keep up with the timer because it takes longer than those 10 seconds to do) the timer will not fire more than once per event loop iteration.

Class synopsis

Properties

repeat

If repeat is 0.0 , then it will automatically be stopped once the timeout is reached. If it is positive, then the timer will automatically be configured to trigger again every repeat seconds later, until stopped manually.

remaining

Returns the remaining time until a timer fires. If the timer is active, then this time is relative to the current event loop time, otherwise it's the timeout value currently configured.

That is, after instanciating an EvTimer with an after value of 5.0 and repeat value of 7.0 , remaining returns 5.0 . When the timer is started and one second passes, remaining will return 4.0 . When the timer expires and is restarted, it will return roughly 7.0 (likely slightly less as callback invocation takes some time too), and so on.

Introduction

EvWatcher is a base class for all watchers( EvCheck , EvChild etc.). Since EvWatcher 's constructor is abstract , one can't(and don't need to) create EvWatcher objects directly.

Class synopsis

Properties

is_active

Readonly . TRUE if the watcher is active. FALSE otherwise.

data

User custom data associated with the watcher

is_pending

Readonly .TRUE if the watcher is pending, i.e. it has outstanding events, but its callback has not yet been invoked. FALSE otherwise. As long, as a watcher is pending(but not active), one must not change its priority.

priority

Integer between Ev::MINPRI and Ev::MAXPRI . Pending watchers with higher priority will be invoked before watchers with lower priority, but priority will not keep watchers from being executed(except for EvIdle watchers). EvIdle watchers provide functionality to suppress invocation when higher priority events are pending.