TLibEv

An object-oriented, line-by-line port of libev 4.33 to Delphi and Free Pascal / Lazarus.

• Version: TLibEv 1.0 (an original library, versioned on its own; it ports libev 4.33)
• Platforms: Linux (epoll or poll backend), macOS (poll backend) and Windows (winsock select backend)
• Architectures: Linux on x86-64, ARM64 (aarch64) and 32-bit ARM, and macOS on Apple Silicon — Free Pascal takes its platform types and syscalls from the RTL, so they are laid out per OS and architecture; Windows on x86/x64. macOS is a Free Pascal target; Delphi's Linux target is x86-64 only.
• Compilers: Delphi 12+/13 (dcc32, dcc64, dcclinux64) and FPC 3.2+ ({$MODE DELPHI})
• License: 2-clause BSD (see LICENSE; derivative of libev, BSD option exercised)

Every method is annotated with an ev.c:NNNN name comment pointing at the corresponding line of the upstream libev 4.33 C source, so the port can be audited against it side by side. The C source itself is not redistributed here — fetch it from the link above if you want to follow the references.

Installation

There is no package to install and no external dependency: just add src/LibEv.pas to your project (or put its folder on your unit search path) and uses LibEv.

Full manual: docs/MANUAL.md - a faithful adaptation of libev's ev.pod documentation to this port's API, covering loop semantics, every watcher type in depth, common idioms and algorithmic complexities.

Watchers

Class	libev type	Purpose
TEvIo	ev_io	fd readable/writable
TEvTimer	ev_timer	relative timer (monotonic clock), Again, Remaining
TEvPeriodic	ev_periodic	wall-clock timer with interval/reschedule callback
TEvSignal	ev_signal	signals (sigaction on Linux, CRT signal() on Windows)
TEvChild	ev_child	child process status via SIGCHLD (Linux only, default loop)
TEvStat	ev_stat	path attribute changes; inotify fast path on Linux, timed polling elsewhere
TEvIdle	ev_idle	runs when nothing else is pending
TEvPrepare / TEvCheck	ev_prepare / ev_check	around each poll
TEvFork	ev_fork	fires in the child after LoopFork
TEvCleanup	ev_cleanup	fires when the loop is destroyed
TEvAsync	ev_async	thread-safe loop wakeup (Send)

Plus TEvLoop.Once (ev_once), TEvLoop.Verify (ev_verify), Suspend/Resume, Ref/Unref, IoCollectInterval/TimeoutCollectInterval.

Example

uses LibEv;

type
  TApp = class
    procedure OnTick(Loop: TEvLoop; W: TEvWatcher; RE: TEvEvents);
    procedure OnRead(Loop: TEvLoop; W: TEvWatcher; RE: TEvEvents);
  end;

procedure TApp.OnTick(Loop: TEvLoop; W: TEvWatcher; RE: TEvEvents);
begin
  Writeln('tick at ', Loop.Now:0:3);
end;

procedure TApp.OnRead(Loop: TEvLoop; W: TEvWatcher; RE: TEvEvents);
begin
  // socket TEvIo(W).Fd is readable
end;

var
  Loop: TEvLoop;
  Timer: TEvTimer;
  Io: TEvIo;
  App: TApp;
begin
  App := TApp.Create;
  Loop := TEvLoop.Default;

  Timer := TEvTimer.Create(1.0, 1.0); // after 1s, repeat every 1s
  Timer.OnTimeout := App.OnTick;
  Timer.Start(Loop);

  Io := TEvIo.Create(SocketFd, [evRead]);
  Io.OnEvent := App.OnRead;
  Io.Start(Loop);

  Loop.Run;
end;

The examples/ folder has a self-testing program for every feature:

Demo	Shows
TimerDemo	timers and periodics
IoDemo / EchoDemo	socket I/O (UDP; a full non-blocking TCP echo server)
AsyncDemo	cross-thread wakeup with TEvAsync
SignalDemo	signal and child watchers, forking a child (Linux)
SignalSelfDemo	signal watcher, raising SIGINT to self (Linux and Windows)
SignalFdDemo	signal delivery via signalfd, evflagSignalFd (Linux)
ForkDemo	fork watcher (Linux)
StatDemo	path watching, Once and cleanup watchers
LoopHooksDemo	TEvPrepare / TEvCheck / TEvIdle
TimeoutDemo	the inactivity-timeout idiom with Again
PriorityDemo	watcher priorities
ExtrasDemo	FeedEvent, Suspend/Resume, collect intervals
HooksDemo	Invoke, FeedFdEvent, invoke-pending / release-acquire hooks
PollDemo	selecting the poll backend explicitly (Linux)
KeyDemo	one event per keypress, with Unicode (interactive)
UartLoopbackDemo	event-driven serial I/O (Linux via a PTY pair; Windows on a real COM port with a physical RX↔TX loopback)

Every demo except the interactive KeyDemo drives its own scenario and exits non-zero on failure, so they double as the test suite that CI runs.

Building

Windows (Delphi):

cd examples
dcc64 -B "-NSSystem;Winapi;System.Win" -U..\src -E..\bin EchoDemo.dpr

Linux (Delphi cross-compile; SDK installed via PAServer, e.g. ubuntu24.04.sdk):

$sdk = "$env:USERPROFILE\Documents\Embarcadero\Studio\SDKs\ubuntu24.04.sdk"
$bds = 'C:\Program Files (x86)\Embarcadero\Studio\37.0'
$lp  = "$bds\lib\linux64\release;$sdk\lib\x86_64-linux-gnu;$sdk\usr\lib\x86_64-linux-gnu;$sdk\usr\lib\gcc\x86_64-linux-gnu\13"
dcclinux64 -B -U..\src -E..\binlinux "--syslibroot:$sdk" "--libpath:$lp" EchoDemo.dpr

Linux (FPC):

cd examples
fpc -Mdelphi -Sh -Fu../src EchoDemo.dpr

Define EV_VERIFY_2 to run the ev_verify consistency checks on every loop iteration (debug builds).

Backends and extras

• Backends: epoll (default) or poll on Linux, poll on macOS, select on Windows. Request one with TEvLoop.Create([], [evbackendPoll]); the choice is fixed for the loop's lifetime. EvSupportedBackends/EvRecommendedBackends report them.
• Signals: sigaction on Linux/macOS, signalfd with evflagSignalFd (Linux), or the CRT signal() on Windows.
• timerfd time-jump detection is used by default on Linux (disable with evflagNoTimerFd).
• Extensibility: EvSetSyserrCb, Watcher.Invoke, Loop.FeedFdEvent, SetInvokePendingCb, SetLoopReleaseCb (threaded loop sharing).
• Platform layer: on Free Pascal the OS types, structs and syscalls come from the RTL units (BaseUnix, UnixType, Linux), which define them per OS and architecture — that is what makes the same source correct on Linux (x86-64, arm64, arm32) and macOS. Delphi/Linux keeps hand-written x86-64 bindings (its Linux compiler targets x86-64 only). The Linux-only kernel interfaces (epoll, inotify, eventfd, signalfd, timerfd) and child watchers are absent on macOS, where signals use sigaction, TEvStat polls, and the wakeup pipe is a plain pipe.

Notes / deviations from C

• Event masks are Pascal sets (TEvEvents); enum ordinals equal the C bit numbers.
• On Windows an "fd" is the SOCKET value itself (no CRT fd layer).
• Watchers are objects owned by the caller; destroying an active watcher stops it first.
• Backend selection has no fallback chain (a failed backend raises rather than trying the next), and LIBEV_FLAGS is not consulted.
• On macOS the poll backend is used (the native kqueue backend is not ported); TEvChild is Linux-only (as in libev on non-Linux).
• Not ported: ev_embed (needs embeddable backends like kqueue), the kqueue / Solaris ports / Linux aio / io_uring backends, custom allocators, and ev_walk (off by default in C too).

Testing

Each program in examples/ is self-checking (it drives the loop and verifies the observed behaviour, returning a non-zero exit code on failure). On every push, CI compiles and runs them with Free Pascal on:

• Linux x86-64, Windows and macOS (Apple Silicon) hosted runners,
• Linux ARM64 (a hosted ubuntu-24.04-arm runner),
• Linux 32-bit ARM (an armhf container under QEMU emulation).