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.TH curl_easy_pause 3 "17 Dec 2007" "libcurl 7.18.0" "libcurl Manual"
.SH NAME
curl_easy_pause - pause and unpause a connection
Using this function, you can explicitly mark a running connection to get
paused, and you can unpause a connection that was previously paused.
-A connection can be paused by using this function or by letting the read
-or the write callbacks return the proper magic return code
+A connection can be paused by using this function or by letting the read or
+the write callbacks return the proper magic return code
(\fICURL_READFUNC_PAUSE\fP and \fICURL_WRITEFUNC_PAUSE\fP). A write callback
that returns pause signals to the library that it couldn't take care of any
data at all, and that data will then be delivered again to the callback when
the writing is later unpaused.
-NOTE: while it may feel tempting, take care and notice that you cannot call
-this function from another thread.
+While it may feel tempting, take care and notice that you cannot call this
+function from another thread. To unpause, you may for example call it from the
+progress callback (\fICURLOPT_PROGRESSFUNCTION(3)\fP), which gets called at
+least once per second, even if the connection is paused.
When this function is called to unpause reading, the chance is high that you
will get your write callback called before this function returns.
.IP CURLPAUSE_RECV
Pause receiving data. There will be no data received on this connection until
this function is called again without this bit set. Thus, the write callback
-(\fICURLOPT_WRITEFUNCTION\fP) won't be called.
+(\fICURLOPT_WRITEFUNCTION(3)\fP) won't be called.
.IP CURLPAUSE_SEND
Pause sending data. There will be no data sent on this connection until this
function is called again without this bit set. Thus, the read callback
-(\fICURLOPT_READFUNCTION\fP) won't be called.
+(\fICURLOPT_READFUNCTION(3)\fP) won't be called.
.IP CURLPAUSE_ALL
Convenience define that pauses both directions.
.IP CURLPAUSE_CONT
CURLE_OK (zero) means that the option was set properly, and a non-zero return
code means something wrong occurred after the new state was set. See the
\fIlibcurl-errors(3)\fP man page for the full list with descriptions.
+.SH LIMITATIONS
+The pausing of transfers does not work with protocols that work without
+network connectivity, like FILE://. Trying to pause such a transfer, in any
+direction, will cause problems in the worst case or an error in the best case.
.SH AVAILABILITY
This function was added in libcurl 7.18.0. Before this version, there was no
explicit support for pausing transfers.
+.SH "USAGE WITH THE MULTI-SOCKET INTERFACE"
+Before libcurl 7.32.0, when a specific handle was unpaused with this function,
+there was no particular forced rechecking or similar of the socket's state,
+which made the continuation of the transfer get delayed until next
+multi-socket call invoke or even longer. Alternatively, the user could
+forcibly call for example curl_multi_socket_all(3) - with a rather hefty
+performance penalty.
+
+Starting in libcurl 7.32.0, unpausing a transfer will schedule a timeout
+trigger for that handle 1 millisecond into the future, so that a
+curl_multi_socket_action( ... CURL_SOCKET_TIMEOUT) can be used immediately
+afterwards to get the transfer going again as desired.
.SH "MEMORY USE"
When pausing a read by returning the magic return code from a write callback,
the read data is already in libcurl's internal buffers so it'll have to keep
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