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Re: Thread issues in svnserve

From: Philip Martin <philip.martin_at_wandisco.com>
Date: Fri, 10 May 2013 10:16:55 +0100

Ivan Zhakov <ivan_at_visualsvn.com> writes:

> Another way add some kind of svn__shared_pool_t with atomic reference
> counter and destroying attached pool when counter reaches zero.
>
> Something like this:

An implementation of your idea:

Index: subversion/svnserve/svnserve.c
===================================================================
--- subversion/svnserve/svnserve.c (revision 1480899)
+++ subversion/svnserve/svnserve.c (working copy)
@@ -53,6 +53,7 @@
 
 #include "private/svn_dep_compat.h"
 #include "private/svn_cmdline_private.h"
+#include "private/svn_atomic.h"
 
 #include "winservice.h"
 
@@ -378,11 +379,44 @@ static apr_status_t redirect_stdout(void *arg)
   return apr_file_dup2(out_file, err_file, pool);
 }
 
+#if APR_HAS_THREADS
+/* The pool passed to apr_thread_create can only be released when both
+
+ A: the call to apr_thread_create has returned to the calling thread
+ B: the new thread has started running and reached apr_thread_start_t
+
+ So we set the atomic counter to 2 then both the calling thread and
+ the new thread decrease it and when it reaches 0 the pool can be
+ released. */
+struct shared_pool_t {
+ svn_atomic_t count;
+ apr_pool_t *pool;
+};
+
+static struct shared_pool_t *
+attach_shared_pool(apr_pool_t *pool)
+{
+ struct shared_pool_t *shared = apr_palloc(pool, sizeof(struct shared_pool_t));
+
+ shared->pool = pool;
+ svn_atomic_set(&shared->count, 2);
+
+ return shared;
+}
+
+static void
+release_shared_pool(struct shared_pool_t *shared)
+{
+ if (svn_atomic_dec(&shared->count) == 0)
+ svn_pool_destroy(shared->pool);
+}
+#endif
+
 /* "Arguments" passed from the main thread to the connection thread */
 struct serve_thread_t {
   svn_ra_svn_conn_t *conn;
   serve_params_t *params;
- apr_pool_t *pool;
+ struct shared_pool_t *shared_pool;
 };
 
 #if APR_HAS_THREADS
@@ -390,8 +424,8 @@ static void * APR_THREAD_FUNC serve_thread(apr_thr
 {
   struct serve_thread_t *d = data;
 
- svn_error_clear(serve(d->conn, d->params, d->pool));
- svn_pool_destroy(d->pool);
+ svn_error_clear(serve(d->conn, d->params, d->shared_pool->pool));
+ release_shared_pool(d->shared_pool);
 
   return NULL;
 }
@@ -455,6 +489,7 @@ int main(int argc, const char *argv[])
 #if APR_HAS_THREADS
   apr_threadattr_t *tattr;
   apr_thread_t *tid;
+ struct shared_pool_t *shared_pool;
 
   struct serve_thread_t *thread_data;
 #endif
@@ -1093,6 +1128,7 @@ int main(int argc, const char *argv[])
              particularly sophisticated strategy for a threaded server, it's
              little different from forking one process per connection. */
 #if APR_HAS_THREADS
+ shared_pool = attach_shared_pool(connection_pool);
           status = apr_threadattr_create(&tattr, connection_pool);
           if (status)
             {
@@ -1112,9 +1148,9 @@ int main(int argc, const char *argv[])
           thread_data = apr_palloc(connection_pool, sizeof(*thread_data));
           thread_data->conn = conn;
           thread_data->params = &params;
- thread_data->pool = connection_pool;
+ thread_data->shared_pool = shared_pool;
           status = apr_thread_create(&tid, tattr, serve_thread, thread_data,
- connection_pool);
+ shared_pool->pool);
           if (status)
             {
               err = svn_error_wrap_apr(status, _("Can't create thread"));
@@ -1122,6 +1158,7 @@ int main(int argc, const char *argv[])
               svn_error_clear(err);
               exit(1);
             }
+ release_shared_pool(shared_pool);
 #endif
           break;
 

-- 
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Received on 2013-05-10 11:17:53 CEST

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