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Richard W.M. Jones

2023-Feb-22 15:01 UTC

[Libguestfs] [PATCH nbdkit] curl: Try to share as much as possible between handles in the pool

Using the libcurl share interface we can share data between the
separate curl easy handles in the pool.  For more about this see:

https://curl.se/libcurl/c/CURLSHOPT_SHARE.html
https://gist.github.com/bagder/7eccf74f8b6d70b5abefeb7f288dba9b
https://everything.curl.dev/libcurl/sharing
---
 plugins/curl/curldefs.h |  3 +-
 plugins/curl/curl.c     |  4 ++-
 plugins/curl/pool.c     | 75 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/plugins/curl/curldefs.h b/plugins/curl/curldefs.h
index c2a3432fc..d614379d0 100644
--- a/plugins/curl/curldefs.h
+++ b/plugins/curl/curldefs.h
@@ -117,9 +117,10 @@ struct curl_handle {
 };
 
 /* pool.c */
+extern void load_pool (void);
+extern void unload_pool (void);
 extern struct curl_handle *get_handle (void);
 extern void put_handle (struct curl_handle *ch);
-extern void free_all_handles (void);
 
 /* scripts.c */
 extern int do_scripts (struct curl_handle *ch);
diff --git a/plugins/curl/curl.c b/plugins/curl/curl.c
index b5927b5b4..b8624a6f8 100644
--- a/plugins/curl/curl.c
+++ b/plugins/curl/curl.c
@@ -101,6 +101,8 @@ curl_load (void)
     nbdkit_error ("libcurl initialization failed: %d", (int) r);
     exit (EXIT_FAILURE);
   }
+
+  load_pool ();
 }
 
 static void
@@ -112,7 +114,7 @@ curl_unload (void)
   free (password);
   free (proxy_password);
   scripts_unload ();
-  free_all_handles ();
+  unload_pool ();
   curl_global_cleanup ();
 }
 
diff --git a/plugins/curl/pool.c b/plugins/curl/pool.c
index b6f4f8e5f..536123388 100644
--- a/plugins/curl/pool.c
+++ b/plugins/curl/pool.c
@@ -52,6 +52,7 @@
 
 #include <nbdkit-plugin.h>
 
+#include "array-size.h"
 #include "ascii-ctype.h"
 #include "ascii-string.h"
 #include "cleanup.h"
@@ -73,6 +74,18 @@ static int debug_cb (CURL *handle, curl_infotype type,
 static size_t header_cb (void *ptr, size_t size, size_t nmemb, void *opaque);
 static size_t write_cb (char *ptr, size_t size, size_t nmemb, void *opaque);
 static size_t read_cb (void *ptr, size_t size, size_t nmemb, void *opaque);
+static void lock_cb (CURL *handle, curl_lock_data data,
+                     curl_lock_access access, void *userptr);
+static void unlock_cb (CURL *handle, curl_lock_data data,
+                       void *userptr);
+
+/* These locks protect access to the curl share data.  See:
+ * https://gist.github.com/bagder/7eccf74f8b6d70b5abefeb7f288dba9b
+ */
+static pthread_rwlock_t lockarray[CURL_LOCK_DATA_LAST];
+
+/* Curl share data. */
+static CURLSH *share;
 
 /* This lock protects access to the curl_handles vector below. */
 static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
@@ -90,18 +103,46 @@ static curl_handle_list curl_handles = empty_vector;
 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
 static size_t in_use = 0, waiting = 0;
 
-/* Close and free all handles in the pool. */
+/* Initialize pool structures. */
 void
-free_all_handles (void)
+load_pool (void)
 {
   size_t i;
 
+  for (i = 0; i < ARRAY_SIZE (lockarray); ++i)
+    pthread_rwlock_init (&lockarray[i], NULL);
+
+  share = curl_share_init ();
+  if (share == NULL) {
+    nbdkit_error ("curl_share_init: %m");
+    exit (EXIT_FAILURE);
+  }
+  curl_share_setopt (share, CURLSHOPT_LOCKFUNC, lock_cb);
+  curl_share_setopt (share, CURLSHOPT_UNLOCKFUNC, unlock_cb);
+  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_CONNECT);
+  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_COOKIE);
+  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_DNS);
+  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_SSL_SESSION);
+}
+
+void
+unload_pool (void)
+{
+  size_t i;
+
+  /* Close and free all handles in the pool. */
   nbdkit_debug ("free_all_handles: number of curl handles allocated:
%zu",
                 curl_handles.len);
 
   for (i = 0; i < curl_handles.len; ++i)
     free_handle (curl_handles.ptr[i]);
   curl_handle_list_reset (&curl_handles);
+
+  /* Free share data. */
+  curl_share_cleanup (share);
+
+  for (i = 0; i < ARRAY_SIZE (lockarray); ++i)
+    pthread_rwlock_destroy (&lockarray[i]);
 }
 
 /* Get a handle from the pool.
@@ -221,6 +262,9 @@ allocate_handle (void)
     goto err;
   }
 
+  /* Share settings with other handles. */
+  curl_easy_setopt (ch->c, CURLOPT_SHARE, share);
+
   /* Various options we always set.
    *
    * NB: Both here and below constants must be explicitly long because
@@ -519,3 +563,30 @@ free_handle (struct curl_handle *ch)
     curl_slist_free_all (ch->headers_copy);
   free (ch);
 }
+
+static void
+lock_cb (CURL *handle, curl_lock_data data, curl_lock_access access,
+         void *userptr)
+{
+  assert (data < ARRAY_SIZE (lockarray));
+
+  switch (access) {
+  case CURL_LOCK_ACCESS_SHARED:
+    pthread_rwlock_rdlock (&lockarray[data]);
+    break;
+  case CURL_LOCK_ACCESS_SINGLE:
+    pthread_rwlock_wrlock (&lockarray[data]);
+    break;
+  default:
+    /* CURL_LOCK_ACCESS_NONE is never used in the current libcurl code. */
+    abort ();
+  }
+}
+
+static void
+unlock_cb (CURL *handle, curl_lock_data data, void *userptr)
+{
+  assert (data < ARRAY_SIZE (lockarray));
+
+  pthread_rwlock_unlock (&lockarray[data]);
+}
-- 
2.39.0

Laszlo Ersek

2023-Feb-22 15:52 UTC

head link

[Libguestfs] [PATCH nbdkit] curl: Try to share as much as possible between handles in the pool

On 2/22/23 16:01, Richard W.M. Jones wrote:> Using the libcurl share interface we can share data between the
> separate curl easy handles in the pool.  For more about this see:
> 
> https://curl.se/libcurl/c/CURLSHOPT_SHARE.html
> https://gist.github.com/bagder/7eccf74f8b6d70b5abefeb7f288dba9b
> https://everything.curl.dev/libcurl/sharing
> ---
>  plugins/curl/curldefs.h |  3 +-
>  plugins/curl/curl.c     |  4 ++-
>  plugins/curl/pool.c     | 75 +++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 78 insertions(+), 4 deletions(-)
> 
> diff --git a/plugins/curl/curldefs.h b/plugins/curl/curldefs.h
> index c2a3432fc..d614379d0 100644
> --- a/plugins/curl/curldefs.h
> +++ b/plugins/curl/curldefs.h
> @@ -117,9 +117,10 @@ struct curl_handle {
>  };
>  
>  /* pool.c */
> +extern void load_pool (void);
> +extern void unload_pool (void);
>  extern struct curl_handle *get_handle (void);
>  extern void put_handle (struct curl_handle *ch);
> -extern void free_all_handles (void);
>  
>  /* scripts.c */
>  extern int do_scripts (struct curl_handle *ch);
> diff --git a/plugins/curl/curl.c b/plugins/curl/curl.c
> index b5927b5b4..b8624a6f8 100644
> --- a/plugins/curl/curl.c
> +++ b/plugins/curl/curl.c
> @@ -101,6 +101,8 @@ curl_load (void)
>      nbdkit_error ("libcurl initialization failed: %d", (int) r);
>      exit (EXIT_FAILURE);
>    }
> +
> +  load_pool ();
>  }
>  
>  static void
> @@ -112,7 +114,7 @@ curl_unload (void)
>    free (password);
>    free (proxy_password);
>    scripts_unload ();
> -  free_all_handles ();
> +  unload_pool ();
>    curl_global_cleanup ();
>  }
>  
> diff --git a/plugins/curl/pool.c b/plugins/curl/pool.c
> index b6f4f8e5f..536123388 100644
> --- a/plugins/curl/pool.c
> +++ b/plugins/curl/pool.c
> @@ -52,6 +52,7 @@
>  
>  #include <nbdkit-plugin.h>
>  
> +#include "array-size.h"
>  #include "ascii-ctype.h"
>  #include "ascii-string.h"
>  #include "cleanup.h"
> @@ -73,6 +74,18 @@ static int debug_cb (CURL *handle, curl_infotype type,
>  static size_t header_cb (void *ptr, size_t size, size_t nmemb, void
*opaque);
>  static size_t write_cb (char *ptr, size_t size, size_t nmemb, void
*opaque);
>  static size_t read_cb (void *ptr, size_t size, size_t nmemb, void
*opaque);
> +static void lock_cb (CURL *handle, curl_lock_data data,
> +                     curl_lock_access access, void *userptr);
> +static void unlock_cb (CURL *handle, curl_lock_data data,
> +                       void *userptr);
> +
> +/* These locks protect access to the curl share data.  See:
> + * https://gist.github.com/bagder/7eccf74f8b6d70b5abefeb7f288dba9b
> + */
> +static pthread_rwlock_t lockarray[CURL_LOCK_DATA_LAST];
> +
> +/* Curl share data. */
> +static CURLSH *share;
>  
>  /* This lock protects access to the curl_handles vector below. */
>  static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
> @@ -90,18 +103,46 @@ static curl_handle_list curl_handles = empty_vector;
>  static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
>  static size_t in_use = 0, waiting = 0;
>  
> -/* Close and free all handles in the pool. */
> +/* Initialize pool structures. */
>  void
> -free_all_handles (void)
> +load_pool (void)
>  {
>    size_t i;
>  
> +  for (i = 0; i < ARRAY_SIZE (lockarray); ++i)
> +    pthread_rwlock_init (&lockarray[i], NULL);
error checking missing
> +
> +  share = curl_share_init ();
> +  if (share == NULL) {
> +    nbdkit_error ("curl_share_init: %m");
> +    exit (EXIT_FAILURE);
> +  }
> +  curl_share_setopt (share, CURLSHOPT_LOCKFUNC, lock_cb);
> +  curl_share_setopt (share, CURLSHOPT_UNLOCKFUNC, unlock_cb);
> +  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_CONNECT);
> +  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_COOKIE);
> +  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_DNS);
> +  curl_share_setopt (share, CURLSHOPT_SHARE, CURL_LOCK_DATA_SSL_SESSION);
error checking missing
> +}
> +
> +void
> +unload_pool (void)
> +{
> +  size_t i;
> +
> +  /* Close and free all handles in the pool. */
>    nbdkit_debug ("free_all_handles: number of curl handles allocated:
%zu",
>                  curl_handles.len);
>  
>    for (i = 0; i < curl_handles.len; ++i)
>      free_handle (curl_handles.ptr[i]);
>    curl_handle_list_reset (&curl_handles);
> +
> +  /* Free share data. */
> +  curl_share_cleanup (share);
> +
> +  for (i = 0; i < ARRAY_SIZE (lockarray); ++i)
> +    pthread_rwlock_destroy (&lockarray[i]);
>  }
>  
>  /* Get a handle from the pool.
> @@ -221,6 +262,9 @@ allocate_handle (void)
>      goto err;
>    }
>  
> +  /* Share settings with other handles. */
> +  curl_easy_setopt (ch->c, CURLOPT_SHARE, share);
> +
>    /* Various options we always set.
>     *
>     * NB: Both here and below constants must be explicitly long because
> @@ -519,3 +563,30 @@ free_handle (struct curl_handle *ch)
>      curl_slist_free_all (ch->headers_copy);
>    free (ch);
>  }
> +
> +static void
> +lock_cb (CURL *handle, curl_lock_data data, curl_lock_access access,
> +         void *userptr)
> +{
> +  assert (data < ARRAY_SIZE (lockarray));
> +
> +  switch (access) {
> +  case CURL_LOCK_ACCESS_SHARED:
> +    pthread_rwlock_rdlock (&lockarray[data]);
> +    break;
> +  case CURL_LOCK_ACCESS_SINGLE:
> +    pthread_rwlock_wrlock (&lockarray[data]);
> +    break;
we could at least assert the return values
> +  default:
> +    /* CURL_LOCK_ACCESS_NONE is never used in the current libcurl code. */
> +    abort ();
> +  }
> +}
> +
> +static void
> +unlock_cb (CURL *handle, curl_lock_data data, void *userptr)
> +{
> +  assert (data < ARRAY_SIZE (lockarray));
> +
> +  pthread_rwlock_unlock (&lockarray[data]);
same here
> +}
Seems sane to me in general, except for the fact that the documentation
at <https://curl.se/libcurl/c/CURLSHOPT_SHARE.html> writes:

"""
CURL_LOCK_DATA_CONNECT

Put the connection cache in the share object and make all easy handles
using this share object share the connection cache.

Note that due to a known bug, it is not safe to share connections this
way between multiple concurrent threads. [...]
"""

Ugh, what? If it's not safe to share the connection cache between
threads, then CURL_LOCK_DATA_CONNECT is effectively unusable, and no
connection pooling can be done. How does that *not* make this whole curl
facility useless?

The facility in general looks super weird; what sense does it make *not*
to share some particular CURL_LOCK_DATA_xxx?

Laszlo

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