Follow up to r1836032: better flush limits checks and description.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1884304 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/mod/core.xml

@@ -2031,21 +2031,24 @@ filenames</description>
 
 <directivesynopsis>
 <name>FlushMaxPipelined</name>
-<description>Threshold above which pipelined responses are flushed to the
+<description>Maximum number of pipelined responses above which they are flushed
-network</description>
+to the network</description>
 <syntax>FlushMaxPipelined <var>number</var></syntax>
 <default>FlushMaxPipelined 5</default>
 <contextlist><context>server config</context><context>virtual host</context>
-<context>directory</context></contextlist>
+</contextlist>
 <compatibility>2.5 and later</compatibility>
 
 <usage>
-    <p>This directive allows to configure the threshold for pipelined
+    <p>This directive allows to configure the maximum number of pipelined
-    responses, which remain pending so long as pipelined request are handled.
+    responses, which remain pending so long as pipelined request are received.
-    When this limit is reached, are forcibly flushed to the network in blocking
+    When the limit is reached, reponses are forcibly flushed to the network in
-    mode, until passing under the threshold again.</p>
+    blocking mode, until passing under the limit again.</p>
 
-    <p>This threshold helps maintaning constrained memory usage.</p>
+    <p><directive>FlushMaxPipelined</directive> helps constraining memory
+    usage. When set to <var>0</var> pipelining is disabled, when set to
+    <var>-1</var> there is no limit (<directive>FlushMaxThreshold</directive>
+    still applies).</p>
 </usage>
 </directivesynopsis>
 
@@ -2056,15 +2059,19 @@ network</description>
 <syntax>FlushMaxThreshold<var>number-of-bytes</var></syntax>
 <default>FlushMaxThreshold 65536</default>
 <contextlist><context>server config</context><context>virtual host</context>
-<context>directory</context></contextlist>
+</contextlist>
 <compatibility>2.5 and later</compatibility>
 
 <usage>
-    <p>This directive allows to configure the threshold (in bytes) for pending
+    <p>This directive allows to configure the threshold for pending output
-    output data. When this limit is reached, data are forcibly flushed to the
+    data (in bytes). When the limit is reached, data are forcibly flushed to
-    network in blocking mode, until passing under the threshold again.</p>
+    the network in blocking mode, until passing under the limit again.</p>
 
-    <p>This threshold helps maintaning constrained memory usage.</p>
+    <p><directive>FlushMaxThreshold</directive> helps constraining memory
+    usage. When set to <var>0</var> or a too small value there are actually
+    no pending data, but for threaded MPMs there can be more threads busy
+    waiting for the network thus less ones available to handle the other
+    simultaneous connections.</p>
 </usage>
 </directivesynopsis>
 
@@ -4179,19 +4186,20 @@ Protocols h2 http/1.1
 
 <directivesynopsis>
 <name>ReadBufferSize</name>
-<description>Size of the buffers used to read network data</description>
+<description>Size of the buffers used to read data</description>
-<syntax>ReadBufferSize <var>number-of-bytes</var></syntax>
+<syntax>ReadBufferSize <var>bytes</var></syntax>
 <default>ReadBufferSize 8192</default>
 <contextlist><context>server config</context><context>virtual host</context>
 <context>directory</context></contextlist>
 <compatibility>2.5 and later</compatibility>
 
 <usage>
-    <p>This directive allows to configure the size in bytes of the memory
+    <p>This directive allows to configure the size (in bytes) of the memory
-    buffers used to read data from the network.</p>
+    buffer used to read data from the network or files.</p>
 
-    <p>Larger buffer can increase peformances for large data but consume more
+    <p>A larger buffer can increase peformances with larger data, but consumes
-    memory (per connection).</p>
+    more memory per connection. The minimum configurable size is
+    <var>1024</var>.</p>
 </usage>
 </directivesynopsis>
  

server/core.c

@@ -83,8 +83,8 @@
 /* valid in core-conf, but not in runtime r->used_path_info */
 #define AP_ACCEPT_PATHINFO_UNSET 3
 
-#define AP_FLUSH_MAX_THRESHOLD 65536
+#define AP_FLUSH_MAX_THRESHOLD 65535
-#define AP_FLUSH_MAX_PIPELINED 5
+#define AP_FLUSH_MAX_PIPELINED 4
 
 APR_HOOK_STRUCT(
     APR_HOOK_LINK(get_mgmt_items)
@@ -2344,10 +2344,10 @@ static const char *set_read_buf_size(cmd_parms *cmd, void *d_,
     char *end;
 
     if (apr_strtoff(&size, arg, &end, 10)
-            || size < 0 || size > APR_SIZE_MAX || *end)
+            || *end || size < 0 || size > APR_UINT32_MAX)
         return apr_pstrcat(cmd->pool,
                            "parameter must be a number between 0 and "
-                           APR_STRINGIFY(APR_SIZE_MAX) "): ",
+                           APR_STRINGIFY(APR_UINT32_MAX) "): ",
                            arg, NULL);
 
     d->read_buf_size = (apr_size_t)size;
@@ -2364,10 +2364,10 @@ static const char *set_flush_max_threshold(cmd_parms *cmd, void *d_,
     char *end;
 
     if (apr_strtoff(&size, arg, &end, 10)
-            || size <= 0 || size > APR_SIZE_MAX || *end)
+            || *end || size < 0 || size > APR_UINT32_MAX)
         return apr_pstrcat(cmd->pool,
-                           "parameter must be a number between 1 and "
+                           "parameter must be a number between 0 and "
-                           APR_STRINGIFY(APR_SIZE_MAX) "): ",
+                           APR_STRINGIFY(APR_UINT32_MAX) "): ",
                            arg, NULL);
 
     conf->flush_max_threshold = (apr_size_t)size;
@@ -2384,9 +2384,9 @@ static const char *set_flush_max_pipelined(cmd_parms *cmd, void *d_,
     char *end;
 
     if (apr_strtoff(&num, arg, &end, 10)
-            || num < 0 || num > APR_INT32_MAX || *end)
+            || *end || num < -1 || num > APR_INT32_MAX)
         return apr_pstrcat(cmd->pool,
-                           "parameter must be a number between 0 and "
+                           "parameter must be a number between -1 and "
                            APR_STRINGIFY(APR_INT32_MAX) ": ",
                            arg, NULL);
 
@@ -2395,7 +2395,6 @@ static const char *set_flush_max_pipelined(cmd_parms *cmd, void *d_,
     return NULL;
 }
 
-
 /*
  * Report a missing-'>' syntax error.
  */
@@ -4733,9 +4732,10 @@ AP_INIT_TAKE1("EnableSendfile", set_enable_sendfile, NULL, OR_FILEINFO,
 AP_INIT_TAKE1("ReadBufferSize", set_read_buf_size, NULL, ACCESS_CONF|RSRC_CONF,
   "Size (in bytes) of the memory buffers used to read data"),
 AP_INIT_TAKE1("FlushMaxThreshold", set_flush_max_threshold, NULL, RSRC_CONF,
-  "Maximum size (in bytes) above which pending data are flushed (blocking) to the network"),
+  "Maximum threshold above which pending data are flushed to the network"),
 AP_INIT_TAKE1("FlushMaxPipelined", set_flush_max_pipelined, NULL, RSRC_CONF,
-  "Number of pipelined/pending responses above which they are flushed to the network"),
+  "Maximum number of pipelined responses (pending) above which they are "
+  "flushed to the network"),
 
 /* Old server config file commands */
 

server/core_filters.c

@@ -610,7 +610,7 @@ static apr_status_t send_brigade_nonblocking(apr_socket_t *s,
          * we are at the end of the brigade, the write will happen outside
          * the loop anyway).
          */
-        if (nbytes >= conf->flush_max_threshold
+        if (nbytes > conf->flush_max_threshold
                 && next != APR_BRIGADE_SENTINEL(bb)
                 && !is_in_memory_bucket(next)) {
             (void)apr_socket_opt_set(s, APR_TCP_NOPUSH, 1);

server/util_filter.c

@@ -1104,7 +1104,7 @@ AP_DECLARE(apr_status_t) ap_filter_reinstate_brigade(ap_filter_t *f,
      *     sent to the client.)
      *
      *  c) The brigade contains at least flush_max_pipelined EOR buckets: do
-     *     blocking writes until the last EOR above flush_max_pipelined.
+     *     blocking writes until after the last EOR above flush_max_pipelined.
      *     (The point of this rule is to prevent too many FDs being kept open
      *     by pipelined requests, possibly allowing a DoS).
      *
@@ -1140,14 +1140,15 @@ AP_DECLARE(apr_status_t) ap_filter_reinstate_brigade(ap_filter_t *f,
         }
 
         if (APR_BUCKET_IS_FLUSH(bucket)
-            || memory_bytes_in_brigade >= conf->flush_max_threshold
+            || (memory_bytes_in_brigade > conf->flush_max_threshold)
-            || eor_buckets_in_brigade >= conf->flush_max_pipelined) {
+            || (conf->flush_max_pipelined >= 0
+                && eor_buckets_in_brigade > conf->flush_max_pipelined)) {
             /* this segment of the brigade MUST be sent before returning. */
 
             if (APLOGctrace6(f->c)) {
                 char *reason = APR_BUCKET_IS_FLUSH(bucket) ?
                                "FLUSH bucket" :
-                               (memory_bytes_in_brigade >= conf->flush_max_threshold) ?
+                               (memory_bytes_in_brigade > conf->flush_max_threshold) ?
                                "max threshold" : "max requests in pipeline";
                 ap_log_cerror(APLOG_MARK, APLOG_TRACE6, 0, f->c,
                               "will flush because of %s", reason);