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curl_multi_poll: a sister to curl_multi_wait() that waits more

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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
This commit is contained in:
Daniel Stenberg 2019-07-29 13:41:00 +02:00
parent cee7639b79
commit 02346abc32
No known key found for this signature in database
GPG key ID: 5CC908FDB71E12C2
9 changed files with 160 additions and 79 deletions
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40
lib/multi.c
View file

@ -974,12 +974,12 @@ CURLMcode curl_multi_fdset(struct Curl_multi *multi,
#define NUM_POLLS_ON_STACK 10
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 */
static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
struct curl_waitfd extra_fds[],
unsigned int extra_nfds,
int timeout_ms,
int *ret,
bool extrawait) /* when no socket, wait */
{
struct Curl_easy *data;
curl_socket_t sockbunch[MAX_SOCKSPEREASYHANDLE];
@ -993,9 +993,6 @@ CURLMcode Curl_multi_wait(struct Curl_multi *multi,
struct pollfd a_few_on_stack[NUM_POLLS_ON_STACK];
struct pollfd *ufds = &a_few_on_stack[0];
if(gotsocket)
*gotsocket = FALSE;
if(!GOOD_MULTI_HANDLE(multi))
return CURLM_BAD_HANDLE;
@ -1124,9 +1121,19 @@ CURLMcode Curl_multi_wait(struct Curl_multi *multi,
free(ufds);
if(ret)
*ret = retcode;
if(gotsocket && (extra_fds || curlfds))
if(!extrawait || extra_fds || curlfds)
/* if any socket was checked */
*gotsocket = TRUE;
;
else {
long sleep_ms = 0;
/* Avoid busy-looping when there's nothing particular to wait for */
if(!curl_multi_timeout(multi, &sleep_ms) && sleep_ms) {
if(sleep_ms > timeout_ms)
sleep_ms = timeout_ms;
Curl_wait_ms((int)sleep_ms);
}
}
return CURLM_OK;
}
@ -1137,7 +1144,16 @@ CURLMcode curl_multi_wait(struct Curl_multi *multi,
int timeout_ms,
int *ret)
{
return Curl_multi_wait(multi, extra_fds, extra_nfds, timeout_ms, ret, NULL);
return Curl_multi_wait(multi, extra_fds, extra_nfds, timeout_ms, ret, FALSE);
}
CURLMcode curl_multi_poll(struct Curl_multi *multi,
struct curl_waitfd extra_fds[],
unsigned int extra_nfds,
int timeout_ms,
int *ret)
{
return Curl_multi_wait(multi, extra_fds, extra_nfds, timeout_ms, ret, TRUE);
}
/*