From 4869f7e4e023a802c535a036011083ff425d7fec Mon Sep 17 00:00:00 2001
From: root <root>
Date: Tue, 6 May 2008 23:34:16 +0000
Subject: *** empty log message ***

---
 Changes |   4 ++-
 ev.c    |   4 ++-
 ev.pod  | 119 ++++++++++++++++++++++++++++++++++++++++++----------------------
 3 files changed, 84 insertions(+), 43 deletions(-)

diff --git a/Changes b/Changes
index 9f2e296..0e7d962 100644
--- a/Changes
+++ b/Changes
@@ -4,7 +4,9 @@ Revision history for libev, a high-performance and full-featured event loop.
           for better cache-efficiency and increases memory requirements
           by up to two pointers/loop.
         - fix a potential aliasing issue in ev_timer_again.
-        - add/document ev_periodic_at, retract diretc access to ->at.
+        - add/document ev_periodic_at, retract direct access to ->at.
+        - improve ev_stat docs.
+        - add portability requirements section.
 
 3.31 Wed Apr 16 20:45:04 CEST 2008
 	- added last minute fix for ev_poll.c by Brandon Black.
diff --git a/ev.c b/ev.c
index 4065b99..058d7ee 100644
--- a/ev.c
+++ b/ev.c
@@ -522,7 +522,7 @@ ev_sleep (ev_tstamp delay)
 
 /*****************************************************************************/
 
-#define MALLOC_ROUND 4096 // prefer to allocate in chunks of this size, must be 2**n and >> 4 longs
+#define MALLOC_ROUND 4096 /* prefer to allocate in chunks of this size, must be 2**n and >> 4 longs */
 
 int inline_size
 array_nextsize (int elem, int cur, int cnt)
@@ -2118,6 +2118,8 @@ infy_add (EV_P_ ev_stat *w)
       ev_timer_start (EV_A_ &w->timer); /* this is not race-free, so we still need to recheck periodically */
 
       /* monitor some parent directory for speedup hints */
+      /* note that exceeding the hardcoded limit is not a correctness issue, */
+      /* but an efficiency issue only */
       if ((errno == ENOENT || errno == EACCES) && strlen (w->path) < 4096)
         {
           char path [4096];
diff --git a/ev.pod b/ev.pod
index 6ae53b1..0f0b2e3 100644
--- a/ev.pod
+++ b/ev.pod
@@ -1612,11 +1612,12 @@ resource-intensive.
 
 At the time of this writing, only the Linux inotify interface is
 implemented (implementing kqueue support is left as an exercise for the
-reader). Inotify will be used to give hints only and should not change the
-semantics of C<ev_stat> watchers, which means that libev sometimes needs
-to fall back to regular polling again even with inotify, but changes are
-usually detected immediately, and if the file exists there will be no
-polling.
+reader, note, however, that the author sees no way of implementing ev_stat
+semantics with kqueue). Inotify will be used to give hints only and should
+not change the semantics of C<ev_stat> watchers, which means that libev
+sometimes needs to fall back to regular polling again even with inotify,
+but changes are usually detected immediately, and if the file exists there
+will be no polling.
 
 =head3 ABI Issues (Largefile Support)
 
@@ -1651,16 +1652,25 @@ The C<stat ()> syscall only supports full-second resolution portably, and
 even on systems where the resolution is higher, many filesystems still
 only support whole seconds.
 
-That means that, if the time is the only thing that changes, you might
-miss updates: on the first update, C<ev_stat> detects a change and calls
-your callback, which does something. When there is another update within
-the same second, C<ev_stat> will be unable to detect it.
-
-The solution to this is to delay acting on a change for a second (or till
-the next second boundary), using a roughly one-second delay C<ev_timer>
-(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
-is added to work around small timing inconsistencies of some operating
-systems.
+That means that, if the time is the only thing that changes, you can
+easily miss updates: on the first update, C<ev_stat> detects a change and
+calls your callback, which does something. When there is another update
+within the same second, C<ev_stat> will be unable to detect it as the stat
+data does not change.
+
+The solution to this is to delay acting on a change for slightly more
+than second (or till slightly after the next full second boundary), using
+a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
+ev_timer_again (loop, w)>).
+
+The C<.02> offset is added to work around small timing inconsistencies
+of some operating systems (where the second counter of the current time
+might be be delayed. One such system is the Linux kernel, where a call to
+C<gettimeofday> might return a timestamp with a full second later than
+a subsequent C<time> call - if the equivalent of C<time ()> is used to
+update file times then there will be a small window where the kernel uses
+the previous second to update file times but libev might already execute
+the timer callback).
 
 =head3 Watcher-Specific Functions and Data Members
 
@@ -1676,28 +1686,32 @@ be detected and should normally be specified as C<0> to let libev choose
 a suitable value. The memory pointed to by C<path> must point to the same
 path for as long as the watcher is active.
 
-The callback will be receive C<EV_STAT> when a change was detected,
-relative to the attributes at the time the watcher was started (or the
-last change was detected).
+The callback will receive C<EV_STAT> when a change was detected, relative
+to the attributes at the time the watcher was started (or the last change
+was detected).
 
 =item ev_stat_stat (loop, ev_stat *)
 
 Updates the stat buffer immediately with new values. If you change the
-watched path in your callback, you could call this fucntion to avoid
-detecting this change (while introducing a race condition). Can also be
-useful simply to find out the new values.
+watched path in your callback, you could call this function to avoid
+detecting this change (while introducing a race condition if you are not
+the only one changing the path). Can also be useful simply to find out the
+new values.
 
 =item ev_statdata attr [read-only]
 
-The most-recently detected attributes of the file. Although the type is of
+The most-recently detected attributes of the file. Although the type is
 C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
-suitable for your system. If the C<st_nlink> member is C<0>, then there
-was some error while C<stat>ing the file.
+suitable for your system, but you can only rely on the POSIX-standardised
+members to be present. If the C<st_nlink> member is C<0>, then there was
+some error while C<stat>ing the file.
 
 =item ev_statdata prev [read-only]
 
 The previous attributes of the file. The callback gets invoked whenever
-C<prev> != C<attr>.
+C<prev> != C<attr>, or, more precisely, one or more of these members
+differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
+C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
 
 =item ev_tstamp interval [read-only]
 
@@ -1761,7 +1775,7 @@ C<ev_timer> callback invocation).
   ...
   ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
   ev_stat_start (loop, &passwd);
-  ev_timer_init (&timer, timer_cb, 0., 1.01);
+  ev_timer_init (&timer, timer_cb, 0., 1.02);
 
 
 =head2 C<ev_idle> - when you've got nothing better to do...
@@ -1859,7 +1873,7 @@ It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
 priority, to ensure that they are being run before any other watchers
 after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
 too) should not activate ("feed") events into libev. While libev fully
-supports this, they will be called before other C<ev_check> watchers
+supports this, they might get executed before other C<ev_check> watchers
 did their job. As C<ev_check> watchers are often used to embed other
 (non-libev) event loops those other event loops might be in an unusable
 state until their C<ev_check> watcher ran (always remind yourself to
@@ -1884,9 +1898,9 @@ macros, but using them is utterly, utterly and completely pointless.
 There are a number of principal ways to embed other event loops or modules
 into libev. Here are some ideas on how to include libadns into libev
 (there is a Perl module named C<EV::ADNS> that does this, which you could
-use for an actually working example. Another Perl module named C<EV::Glib>
-embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
-into the Glib event loop).
+use as a working example. Another Perl module named C<EV::Glib> embeds a
+Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
+Glib event loop).
 
 Method 1: Add IO watchers and a timeout watcher in a prepare handler,
 and in a check watcher, destroy them and call into libadns. What follows
@@ -3204,15 +3218,21 @@ the form of the C<EVBACKEND_SELECT> backend, and only supports socket
 descriptors. This only applies when using Win32 natively, not when using
 e.g. cygwin.
 
+Lifting these limitations would basically require the full
+re-implementation of the I/O system. If you are into these kinds of
+things, then note that glib does exactly that for you in a very portable
+way (note also that glib is the slowest event library known to man).
+
 There is no supported compilation method available on windows except
 embedding it into other applications.
 
-Due to the many, low, and arbitrary limits on the win32 platform and the
-abysmal performance of winsockets, using a large number of sockets is not
-recommended (and not reasonable). If your program needs to use more than
-a hundred or so sockets, then likely it needs to use a totally different
-implementation for windows, as libev offers the POSIX model, which cannot
-be implemented efficiently on windows (microsoft monopoly games).
+Due to the many, low, and arbitrary limits on the win32 platform and
+the abysmal performance of winsockets, using a large number of sockets
+is not recommended (and not reasonable). If your program needs to use
+more than a hundred or so sockets, then likely it needs to use a totally
+different implementation for windows, as libev offers the POSIX readyness
+notification model, which cannot be implemented efficiently on windows
+(microsoft monopoly games).
 
 =over 4
 
@@ -3236,11 +3256,13 @@ complexity in the O(n²) range when using win32.
 
 =item Limited number of file descriptors
 
-Windows has numerous arbitrary (and low) limits on things. Early versions
-of winsocket's select only supported waiting for a max. of C<64> handles
-(probably owning to the fact that all windows kernels can only wait for
-C<64> things at the same time internally; microsoft recommends spawning a
-chain of threads and wait for 63 handles and the previous thread in each).
+Windows has numerous arbitrary (and low) limits on things.
+
+Early versions of winsocket's select only supported waiting for a maximum
+of C<64> handles (probably owning to the fact that all windows kernels
+can only wait for C<64> things at the same time internally; microsoft
+recommends spawning a chain of threads and wait for 63 handles and the
+previous thread in each. Great).
 
 Newer versions support more handles, but you need to define C<FD_SETSIZE>
 to some high number (e.g. C<2048>) before compiling the winsocket select
@@ -3289,6 +3311,21 @@ The most portable way to handle signals is to block signals in all threads
 except the initial one, and run the default loop in the initial thread as
 well.
 
+=item C<long> must be large enough for common memory allocation sizes
+
+To improve portability and simplify using libev, libev uses C<long>
+internally instead of C<size_t> when allocating its data structures. On
+non-POSIX systems (Microsoft...) this might be unexpectedly low, but
+is still at least 31 bits everywhere, which is enough for hundreds of
+millions of watchers.
+
+=item C<double> must hold a time value in seconds with enough accuracy
+
+The type C<double> is used to represent timestamps. It is required to have
+at least 51 bits of mantissa, which is good enough for at least into the
+year 4000. This requirement is fulfilled by implementations implementing
+IEEE 754 (basically all existing ones).
+
 =back
 
 If you know of other additional requirements drop me a note.
-- 
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