[Rd] Big speedup in install.packages() by re-using connections

[Tomas Kalibera]

On 4/25/24 17:01, Ivan Krylov via R-devel wrote:
> On Thu, 25 Apr 2024 14:45:04 +0200
> Jeroen Ooms <jeroenooms using gmail.com> wrote:
>
>> Thoughts?
> How verboten would it be to create an empty external pointer object,
> add it to the preserved list, and set an on-exit finalizer to clean up
> the curl multi-handle? As far as I can tell, the internet module is not
> supposed to be unloaded, so this would not introduce an opportunity to
> jump to an unmapped address. This makes it possible to avoid adding a
> CurlCleanup() function to the internet module:

Cleaning up this way in principle would probably be fine, but R already 
has support for re-using connections. Even more, R can download files in 
parallel (in a single thread), which particularly helps with bigger 
latencies (e.g. typically users connecting from home, etc). See 
?download.file(), look for "simultaneous".

I've improved the existing support in R-devel and made it the default in 
install.packages() and download.packages(). I am seeing speedups 
somewhere between 2x and 9x on several systems (with quiet=TRUE) when 
downloading many packages.

Sequential downloads by default (quiet=FALSE) show a progress bar, which 
can be rather slow, particularly on Windows. Turning that off can help 
with slow downloads in already released versions of R. Consequently, via 
disabling the progress bar, the speedups with R-devel could seem even 
bigger than the range.

A common practice when installing/checking say all packages from CRAN or 
Bioconductor is to set up a local mirror of the repositories and 
download/update it with "rsync". When R then "downloads" packages from 
the local mirror using the "file://" protocol, it completely avoids 
these problems. The increased performance of download in R-devel cannot 
beat this setup.

However, the improvement should help a little bit users installing 
binary packages (on Windows, macOS), where the download time can play a 
visible role, when they install packages with many (uninstalled) 
dependencies. Users installing from source, particularly with packages 
needing compilation, would probably not notice.

Tomas


>
> Index: src/modules/internet/libcurl.c
> ===================================================================
> --- src/modules/internet/libcurl.c	(revision 86484)
> +++ src/modules/internet/libcurl.c	(working copy)
> @@ -55,6 +55,47 @@
>   
>   static int current_timeout = 0;
>   
> +// The multi-handle is shared between downloads for reusing connections
> +static CURLM *shared_mhnd = NULL;
> +static SEXP mhnd_sentinel = NULL;
> +
> +static void cleanup_mhnd(SEXP ignored)
> +{
> +    if(shared_mhnd){
> +        curl_multi_cleanup(shared_mhnd);
> +        shared_mhnd = NULL;
> +    }
> +    curl_global_cleanup();
> +}
> +static void rollback_mhnd_sentinel(void* sentinel) {
> +    // Failed to allocate memory while registering a finalizer,
> +    // therefore must release the object
> +    R_ReleaseObject((SEXP)sentinel);
> +}
> +static CURLM *get_mhnd(void)
> +{
> +    if (!mhnd_sentinel) {
> +      SEXP sentinel = PROTECT(R_MakeExternalPtr(NULL, R_NilValue, R_NilValue));
> +      R_PreserveObject(sentinel);
> +      UNPROTECT(1);
> +      // Avoid leaking the sentinel before setting the finalizer
> +      RCNTXT cntxt;
> +      begincontext(&cntxt, CTXT_CCODE, R_NilValue, R_BaseEnv, R_BaseEnv,
> +                   R_NilValue, R_NilValue);
> +      cntxt.cend = &rollback_mhnd_sentinel;
> +      cntxt.cenddata = sentinel;
> +      R_RegisterCFinalizerEx(sentinel, cleanup_mhnd, TRUE);
> +      // Succeeded, no need to clean up if endcontext() fails allocation
> +      mhnd_sentinel = sentinel;
> +      cntxt.cend = NULL;
> +      endcontext(&cntxt);
> +    }
> +    if(!shared_mhnd) {
> +      shared_mhnd = curl_multi_init();
> +    }
> +    return shared_mhnd;
> +}
> +
>   # if LIBCURL_VERSION_MAJOR < 7 || (LIBCURL_VERSION_MAJOR == 7 && LIBCURL_VERSION_MINOR < 28)
>   
>   // curl/curl.h includes <sys/select.h> and headers it requires.
> @@ -565,8 +606,6 @@
>   	if (c->hnd && c->hnd[i])
>   	    curl_easy_cleanup(c->hnd[i]);
>       }
> -    if (c->mhnd)
> -	curl_multi_cleanup(c->mhnd);
>       if (c->headers)
>   	curl_slist_free_all(c->headers);
>   
> @@ -668,7 +707,7 @@
>   	c.headers = headers = tmp;
>       }
>   
> -    CURLM *mhnd = curl_multi_init();
> +    CURLM *mhnd = get_mhnd();
>       if (!mhnd)
>   	error(_("could not create curl handle"));
>       c.mhnd = mhnd;
>
>