curl_multi_poll: a sister to curl_multi_wait() that waits more

Repeatedly we see problems where using curl_multi_wait() is difficult or
just awkward because if it has no file descriptor to wait for
internally, it returns immediately and leaves it to the caller to wait
for a small amount of time in order to avoid occasional busy-looping.

This is often missed or misunderstood, leading to underperforming
applications.

This change introduces curl_multi_poll() as a replacement drop-in
function that accepts the exact same set of arguments. This function
works identically to curl_multi_wait() - EXCEPT - for the case when
there's nothing to wait for internally, as then this function will by
itself wait for a "suitable" short time before it returns. This
effectiely avoids all risks of busy-looping and should also make it less
likely that apps "over-wait".

This also changes the curl tool to use this funtion internally when
doing parallel transfers and changes curl_easy_perform() to use it
internally.

Closes #4163

1 files changed, 0 insertions, 7 deletions

diff --git a/lib/multiif.h b/lib/multiif.h
index 57b6145eb..0755a7cd2 100644
--- a/lib/multiif.h
+++ b/lib/multiif.h
@@ -89,11 +89,4 @@ CURLMcode Curl_multi_add_perform(struct Curl_multi *multi,
                                  struct Curl_easy *data,
                                  struct connectdata *conn);
 
-CURLMcode Curl_multi_wait(struct Curl_multi *multi,
-                          struct curl_waitfd extra_fds[],
-                          unsigned int extra_nfds,
-                          int timeout_ms,
-                          int *ret,
-                          bool *gotsocket); /* if any socket was checked */
-
 #endif /* HEADER_CURL_MULTIIF_H */