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@ -132,7 +132,7 @@ |
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.\" ======================================================================== |
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.\" |
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.IX Title "LIBEV 3" |
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.TH LIBEV 3 "2008-05-11" "libev-3.33" "libev - high perfromance full featured event loop" |
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.TH LIBEV 3 "2008-05-22" "libev-3.41" "libev - high perfromance full featured event loop" |
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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.\" way too many mistakes in technical documents. |
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.if n .ad l |
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@ -254,6 +254,25 @@ to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculati |
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it, you should treat it as some floatingpoint value. Unlike the name |
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component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences |
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throughout libev. |
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.SH "ERROR HANDLING" |
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.IX Header "ERROR HANDLING" |
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Libev knows three classes of errors: operating system errors, usage errors |
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and internal errors (bugs). |
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.PP |
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When libev catches an operating system error it cannot handle (for example |
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a syscall indicating a condition libev cannot fix), it calls the callback |
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set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or |
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abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort |
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()\*(C'\fR. |
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.PP |
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When libev detects a usage error such as a negative timer interval, then |
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it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism, |
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so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in |
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the libev caller and need to be fixed there. |
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.PP |
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Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has |
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extensive consistency checking code. These do not trigger under normal |
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circumstances, as they indicate either a bug in libev or worse. |
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.SH "GLOBAL FUNCTIONS" |
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.IX Header "GLOBAL FUNCTIONS" |
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These functions can be called anytime, even before initialising the |
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@ -466,7 +485,7 @@ parallelity (most of the file descriptors should be busy). If you are |
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writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many |
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connections as possible during one iteration. You might also want to have |
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a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of |
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readyness notifications you get per iteration. |
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readiness notifications you get per iteration. |
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.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 |
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.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 |
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.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" |
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@ -555,7 +574,7 @@ file descriptor per loop iteration. For small and medium numbers of file |
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descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend |
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might perform better. |
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.Sp |
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On the positive side, ignoring the spurious readyness notifications, this |
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On the positive side, ignoring the spurious readiness notifications, this |
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backend actually performed to specification in all tests and is fully |
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embeddable, which is a rare feat among the OS-specific backends. |
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.ie n .IP """EVBACKEND_ALL""" 4 |
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@ -828,6 +847,16 @@ interval to a value near \f(CW0.1\fR or so, which is often enough for |
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interactive servers (of course not for games), likewise for timeouts. It |
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usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR, |
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as this approsaches the timing granularity of most systems. |
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.IP "ev_loop_verify (loop)" 4 |
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.IX Item "ev_loop_verify (loop)" |
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This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been |
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compiled in. It tries to go through all internal structures and checks |
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them for validity. If anything is found to be inconsistent, it will print |
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an error message to standard error and call \f(CW\*(C`abort ()\*(C'\fR. |
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.Sp |
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This can be used to catch bugs inside libev itself: under normal |
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circumstances, this function will never abort as of course libev keeps its |
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data structures consistent. |
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.SH "ANATOMY OF A WATCHER" |
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.IX Header "ANATOMY OF A WATCHER" |
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A watcher is a structure that you create and register to record your |
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@ -1165,7 +1194,7 @@ If you must do this, then force the use of a known-to-be-good backend |
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\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). |
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.PP |
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Another thing you have to watch out for is that it is quite easy to |
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receive \*(L"spurious\*(R" readyness notifications, that is your callback might |
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receive \*(L"spurious\*(R" readiness notifications, that is your callback might |
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be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block |
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because there is no data. Not only are some backends known to create a |
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lot of those (for example solaris ports), it is very easy to get into |
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@ -1285,8 +1314,8 @@ Timer watchers are simple relative timers that generate an event after a |
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given time, and optionally repeating in regular intervals after that. |
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.PP |
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The timers are based on real time, that is, if you register an event that |
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times out after an hour and you reset your system clock to last years |
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time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because |
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times out after an hour and you reset your system clock to january last |
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year, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because |
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detecting time jumps is hard, and some inaccuracies are unavoidable (the |
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monotonic clock option helps a lot here). |
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.PP |
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@ -1300,7 +1329,7 @@ on the current time, use something like this to adjust for this: |
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\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.); |
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.Ve |
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.PP |
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The callback is guarenteed to be invoked only when its timeout has passed, |
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The callback is guarenteed to be invoked only after its timeout has passed, |
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but if multiple timers become ready during the same loop iteration then |
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order of execution is undefined. |
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.PP |
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@ -1312,16 +1341,17 @@ order of execution is undefined. |
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.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 |
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.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" |
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.PD |
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Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is |
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\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the |
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timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds |
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later, again, and again, until stopped manually. |
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.Sp |
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The timer itself will do a best-effort at avoiding drift, that is, if you |
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configure a timer to trigger every 10 seconds, then it will trigger at |
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exactly 10 second intervals. If, however, your program cannot keep up with |
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the timer (because it takes longer than those 10 seconds to do stuff) the |
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timer will not fire more than once per event loop iteration. |
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Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR |
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is \f(CW0.\fR, then it will automatically be stopped once the timeout is |
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reached. If it is positive, then the timer will automatically be |
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configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again, |
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until stopped manually. |
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.Sp |
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The timer itself will do a best-effort at avoiding drift, that is, if |
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you configure a timer to trigger every 10 seconds, then it will normally |
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trigger at exactly 10 second intervals. If, however, your program cannot |
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keep up with the timer (because it takes longer than those 10 seconds to |
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do stuff) the timer will not fire more than once per event loop iteration. |
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.IP "ev_timer_again (loop, ev_timer *)" 4 |
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.IX Item "ev_timer_again (loop, ev_timer *)" |
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This will act as if the timer timed out and restart it again if it is |
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@ -1410,18 +1440,19 @@ Periodic watchers are also timers of a kind, but they are very versatile |
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.PP |
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Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) |
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but on wallclock time (absolute time). You can tell a periodic watcher |
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to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a |
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to trigger after some specific point in time. For example, if you tell a |
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periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () |
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+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will |
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take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger |
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roughly 10 seconds later). |
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+ 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system |
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clock to january of the previous year, then it will take more than year |
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to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would still trigger |
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roughly 10 seconds later as it uses a relative timeout). |
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.PP |
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They can also be used to implement vastly more complex timers, such as |
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triggering an event on each midnight, local time or other, complicated, |
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rules. |
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\&\f(CW\*(C`ev_periodic\*(C'\fRs can also be used to implement vastly more complex timers, |
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such as triggering an event on each \*(L"midnight, local time\*(R", or other |
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complicated, rules. |
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.PP |
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As with timers, the callback is guarenteed to be invoked only when the |
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time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready |
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time (\f(CW\*(C`at\*(C'\fR) has passed, but if multiple periodic timers become ready |
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during the same loop iteration then order of execution is undefined. |
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.PP |
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\fIWatcher-Specific Functions and Data Members\fR |
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@ -1438,10 +1469,10 @@ operation, and we will explain them from simplest to complex: |
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.IP "\(bu" 4 |
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absolute timer (at = time, interval = reschedule_cb = 0) |
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.Sp |
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In this configuration the watcher triggers an event at the wallclock time |
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\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, |
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that is, if it is to be run at January 1st 2011 then it will run when the |
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system time reaches or surpasses this time. |
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In this configuration the watcher triggers an event after the wallclock |
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time \f(CW\*(C`at\*(C'\fR has passed and doesn't repeat. It will not adjust when a time |
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jump occurs, that is, if it is to be run at January 1st 2011 then it will |
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run when the system time reaches or surpasses this time. |
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.IP "\(bu" 4 |
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repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) |
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.Sp |
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@ -1450,7 +1481,8 @@ In this mode the watcher will always be scheduled to time out at the next |
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and then repeat, regardless of any time jumps. |
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.Sp |
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This can be used to create timers that do not drift with respect to system |
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time: |
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time, for example, here is a \f(CW\*(C`ev_periodic\*(C'\fR that triggers each hour, on |
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the hour: |
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.Sp |
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.Vb 1 |
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\& ev_periodic_set (&periodic, 0., 3600., 0); |
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@ -1467,7 +1499,12 @@ time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time ju |
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.Sp |
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For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near |
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\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for |
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this value. |
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this value, and in fact is often specified as zero. |
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.Sp |
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Note also that there is an upper limit to how often a timer can fire (cpu |
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speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability |
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will of course detoriate. Libev itself tries to be exact to be about one |
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millisecond (if the \s-1OS\s0 supports it and the machine is fast enough). |
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.IP "\(bu" 4 |
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manual reschedule mode (at and interval ignored, reschedule_cb = callback) |
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.Sp |
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@ -1477,12 +1514,14 @@ reschedule callback will be called with the watcher as first, and the |
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current time as second argument. |
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.Sp |
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\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, |
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ever, or make any event loop modifications\fR. If you need to stop it, |
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return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by |
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starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). |
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ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR. |
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.Sp |
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If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop |
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it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the |
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only event loop modification you are allowed to do). |
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.Sp |
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Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
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ev_tstamp now)\*(C'\fR, e.g.: |
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The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic |
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*w, ev_tstamp now)\*(C'\fR, e.g.: |
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.Sp |
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.Vb 4 |
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\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
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@ -1496,11 +1535,11 @@ It must return the next time to trigger, based on the passed time value |
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will usually be called just before the callback will be triggered, but |
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might be called at other times, too. |
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.Sp |
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\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the |
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passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. |
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\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or |
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equal to the passed \f(CI\*(C`now\*(C'\fI value\fR. |
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.Sp |
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This can be used to create very complex timers, such as a timer that |
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triggers on each midnight, local time. To do this, you would calculate the |
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triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the |
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next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How |
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you do this is, again, up to you (but it is not trivial, which is the main |
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reason I omitted it as an example). |
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@ -1799,7 +1838,7 @@ within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it as |
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data does not change. |
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.PP |
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The solution to this is to delay acting on a change for slightly more |
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than second (or till slightly after the next full second boundary), using |
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than a second (or till slightly after the next full second boundary), using |
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a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02); |
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ev_timer_again (loop, w)\*(C'\fR). |
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.PP |
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@ -3088,8 +3127,8 @@ two). |
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.IX Item "EV_USE_4HEAP" |
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Heaps are not very cache-efficient. To improve the cache-efficiency of the |
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timer and periodics heap, libev uses a 4\-heap when this symbol is defined |
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to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has a |
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noticable after performance with many (thousands) of watchers. |
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to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has |
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noticably faster performance with many (thousands) of watchers. |
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.Sp |
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The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR |
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(disabled). |
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@ -3099,11 +3138,23 @@ Heaps are not very cache-efficient. To improve the cache-efficiency of the |
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timer and periodics heap, libev can cache the timestamp (\fIat\fR) within |
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the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR), |
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which uses 8\-12 bytes more per watcher and a few hundred bytes more code, |
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but avoids random read accesses on heap changes. This noticably improves |
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performance noticably with with many (hundreds) of watchers. |
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but avoids random read accesses on heap changes. This improves performance |
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noticably with with many (hundreds) of watchers. |
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.Sp |
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The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR |
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(disabled). |
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.IP "\s-1EV_VERIFY\s0" 4 |
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.IX Item "EV_VERIFY" |
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Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will |
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be done: If set to \f(CW0\fR, no internal verification code will be compiled |
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in. If set to \f(CW1\fR, then verification code will be compiled in, but not |
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called. If set to \f(CW2\fR, then the internal verification code will be |
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called once per loop, which can slow down libev. If set to \f(CW3\fR, then the |
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verification code will be called very frequently, which will slow down |
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libev considerably. |
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.Sp |
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The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be |
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\&\f(CW0.\fR |
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.IP "\s-1EV_COMMON\s0" 4 |
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.IX Item "EV_COMMON" |
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By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining |
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@ -3328,17 +3379,17 @@ Due to the many, low, and arbitrary limits on the win32 platform and |
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the abysmal performance of winsockets, using a large number of sockets |
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is not recommended (and not reasonable). If your program needs to use |
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more than a hundred or so sockets, then likely it needs to use a totally |
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different implementation for windows, as libev offers the \s-1POSIX\s0 readyness |
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different implementation for windows, as libev offers the \s-1POSIX\s0 readiness |
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notification model, which cannot be implemented efficiently on windows |
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(microsoft monopoly games). |
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.IP "The winsocket select function" 4 |
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.IX Item "The winsocket select function" |
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The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it requires |
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socket \fIhandles\fR and not socket \fIfile descriptors\fR. This makes select |
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very inefficient, and also requires a mapping from file descriptors |
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to socket handles. See the discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, |
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\&\f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and \f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor |
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symbols for more info. |
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The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it |
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requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is |
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also extremely buggy). This makes select very inefficient, and also |
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requires a mapping from file descriptors to socket handles. See the |
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discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and |
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\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info. |
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.Sp |
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The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime |
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libraries and raw winsocket select is: |
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@ -3417,12 +3468,62 @@ enough for at least into the year 4000. This requirement is fulfilled by |
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implementations implementing \s-1IEEE\s0 754 (basically all existing ones). |
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.PP |
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If you know of other additional requirements drop me a note. |
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.SH "COMPILER WARNINGS" |
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.IX Header "COMPILER WARNINGS" |
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Depending on your compiler and compiler settings, you might get no or a |
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lot of warnings when compiling libev code. Some people are apparently |
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scared by this. |
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.PP |
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However, these are unavoidable for many reasons. For one, each compiler |
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has different warnings, and each user has different tastes regarding |
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warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when |
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targetting a specific compiler and compiler-version. |
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.PP |
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Another reason is that some compiler warnings require elaborate |
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workarounds, or other changes to the code that make it less clear and less |
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maintainable. |
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.PP |
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And of course, some compiler warnings are just plain stupid, or simply |
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wrong (because they don't actually warn about the cindition their message |
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seems to warn about). |
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.PP |
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While libev is written to generate as few warnings as possible, |
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\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev |
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with any compiler warnings enabled unless you are prepared to cope with |
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them (e.g. by ignoring them). Remember that warnings are just that: |
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warnings, not errors, or proof of bugs. |
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.SH "VALGRIND" |
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.IX Header "VALGRIND" |
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Valgrind has a special section here because it is a popular tool that is |
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highly useful, but valgrind reports are very hard to interpret. |
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.PP |
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If you think you found a bug (memory leak, uninitialised data access etc.) |
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in libev, then check twice: If valgrind reports something like: |
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.PP |
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.Vb 3 |
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\& ==2274== definitely lost: 0 bytes in 0 blocks. |
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\& ==2274== possibly lost: 0 bytes in 0 blocks. |
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\& ==2274== still reachable: 256 bytes in 1 blocks. |
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.Ve |
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.PP |
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then there is no memory leak. Similarly, under some circumstances, |
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valgrind might report kernel bugs as if it were a bug in libev, or it |
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might be confused (it is a very good tool, but only a tool). |
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.PP |
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If you are unsure about something, feel free to contact the mailing list |
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with the full valgrind report and an explanation on why you think this is |
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a bug in libev. However, don't be annoyed when you get a brisk \*(L"this is |
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no bug\*(R" answer and take the chance of learning how to interpret valgrind |
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properly. |
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.PP |
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If you need, for some reason, empty reports from valgrind for your project |
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I suggest using suppression lists. |
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.SH "AUTHOR" |
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.IX Header "AUTHOR" |
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Marc Lehmann <libev@schmorp.de>. |
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.SH "POD ERRORS" |
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.IX Header "POD ERRORS" |
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Hey! \fBThe above document had some coding errors, which are explained below:\fR |
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.IP "Around line 3052:" 4 |
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.IX Item "Around line 3052:" |
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.IP "Around line 3107:" 4 |
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.IX Item "Around line 3107:" |
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You forgot a '=back' before '=head2' |
Marc Alexander Lehmann
12 years ago