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examples/10-at-a-time.c: improve readability and simplify

 - use better variable names to explain their purposes
 - convert logic to curl_multi_wait()
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bagder committed Mar 1, 2019
1 parent 754ae10 commit 8cf6c170cf310626f8008c25df71f43f2a9061a6
Showing with 25 additions and 72 deletions.
  1. +25 −72 docs/examples/10-at-a-time.c
@@ -5,7 +5,7 @@
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
* Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
@@ -20,10 +20,8 @@
*
***************************************************************************/
/* <DESC>
* Source code using the multi interface to download many
* files, with a capped maximum amount of simultaneous transfers.
* Download many files in parallel, in the same thread.
* </DESC>
* Written by Michael Wallner
*/

#include <errno.h>
@@ -84,92 +82,47 @@ static const char *urls[] = {
"https://www.un.org",
};

#define MAX 10 /* number of simultaneous transfers */
#define CNT sizeof(urls)/sizeof(char *) /* total number of transfers to do */
#define MAX_PARALLEL 10 /* number of simultaneous transfers */
#define NUM_URLS sizeof(urls)/sizeof(char *) /* total number of transfers to do */

static size_t cb(char *d, size_t n, size_t l, void *p)
static size_t write_cb(char *data, size_t n, size_t l, void *userp)
{
/* take care of the data here, ignored in this example */
(void)d;
(void)p;
(void)data;
(void)userp;
return n*l;
}

static void init(CURLM *cm, int i)
static void add_transfer(CURLM *cm, int i)
{
CURL *eh = curl_easy_init();

curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, cb);
curl_easy_setopt(eh, CURLOPT_HEADER, 0L);
curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, write_cb);
curl_easy_setopt(eh, CURLOPT_URL, urls[i]);
curl_easy_setopt(eh, CURLOPT_PRIVATE, urls[i]);
curl_easy_setopt(eh, CURLOPT_VERBOSE, 0L);

curl_multi_add_handle(cm, eh);
}

int main(void)
{
CURLM *cm;
CURLMsg *msg;
long L;
unsigned int C = 0;
int M, Q, U = -1;
fd_set R, W, E;
struct timeval T;
unsigned int transfers = 0;
int msgs_left = -1;
int still_alive = 1;

curl_global_init(CURL_GLOBAL_ALL);

cm = curl_multi_init();

/* we can optionally limit the total amount of connections this multi handle
uses */
curl_multi_setopt(cm, CURLMOPT_MAXCONNECTS, (long)MAX);
/* Limit the amount of simultaneous connections curl should allow: */
curl_multi_setopt(cm, CURLMOPT_MAXCONNECTS, (long)MAX_PARALLEL);

for(C = 0; C < MAX; ++C) {
init(cm, C);
}
for(transfers = 0; transfers < MAX_PARALLEL; transfers++)
add_transfer(cm, transfers);

while(U) {
curl_multi_perform(cm, &U);
do {
curl_multi_perform(cm, &still_alive);

if(U) {
FD_ZERO(&R);
FD_ZERO(&W);
FD_ZERO(&E);

if(curl_multi_fdset(cm, &R, &W, &E, &M)) {
fprintf(stderr, "E: curl_multi_fdset\n");
return EXIT_FAILURE;
}

if(curl_multi_timeout(cm, &L)) {
fprintf(stderr, "E: curl_multi_timeout\n");
return EXIT_FAILURE;
}
if(L == -1)
L = 100;

if(M == -1) {
#ifdef WIN32
Sleep(L);
#else
sleep((unsigned int)L / 1000);
#endif
}
else {
T.tv_sec = L/1000;
T.tv_usec = (L%1000)*1000;

if(0 > select(M + 1, &R, &W, &E, &T)) {
fprintf(stderr, "E: select(%i,,,,%li): %i: %s\n",
M + 1, L, errno, strerror(errno));
return EXIT_FAILURE;
}
}
}

while((msg = curl_multi_info_read(cm, &Q))) {
while((msg = curl_multi_info_read(cm, &msgs_left))) {
if(msg->msg == CURLMSG_DONE) {
char *url;
CURL *e = msg->easy_handle;
@@ -182,13 +135,13 @@ int main(void)
else {
fprintf(stderr, "E: CURLMsg (%d)\n", msg->msg);
}
if(C < CNT) {
init(cm, C++);
U++; /* just to prevent it from remaining at 0 if there are more
URLs to get */
}
if(transfers < NUM_URLS)
add_transfer(cm, transfers++);
}
}
if(still_alive)
curl_multi_wait(cm, NULL, 0, 1000, NULL);

} while(still_alive || (transfers < NUM_URLS));

curl_multi_cleanup(cm);
curl_global_cleanup();

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