Move send_buffer() and send_va_buffer() from net.c to fd.c.

[paraslash.git] / buffer_tree.h

diff --git a/buffer_tree.h b/buffer_tree.h
index 53b24fe3eb3be403cf8fb27e412936adf9b0320e..4d27ec7b8b1a49db01aa4a87fe94b6a7fff0e96c 100644 (file)
--- a/buffer_tree.h
+++ b/buffer_tree.h
@@ -1,44 +1,206 @@
+/*
+ * Copyright (C) 2009-2012 Andre Noll <maan@systemlinux.org>
+ *
+ * Licensed under the GPL v2. For licencing details see COPYING.
+ */
+
+/**
+ * \file buffer_tree.h Buffer tree management.
+ *
+ * \par Buffer trees and buffer tree nodes.
+ * The buffer tree API offers a more powerful method than standard unix pipes
+ * for managing the data flow from the producer of the data (e.g. the network
+ * receiver) to its consumer(s) (e.g. a sound card).
+ *
+ * A buffer tree consists of buffer tree nodes linked via certain parent/child
+ * relationships.
+ *
+ * Each data buffer starts its way from the root of the buffer tree. At each
+ * node the data is investigated and possibly changed. New data is then fed to
+ * each child.  Everything happens within one single-treaded process. There are
+ * no file descriptors and no calls to read() or write().
+ *
+ * Whenever a node in the buffer tree creates output, either by creating a new
+ * buffer or by pushing down buffers received from its parent, references to
+ * that buffer are created for all children of the node. The buffer tree code
+ * tries hard to avoid to copy buffer contents, but is forced to do so in case
+ * there are alignment constraints.
+ *
+ * Communication between nodes is possible via the btr_exec_up() function.
+ * For example, in para_audiod the alsa writer asks all parent nodes
+ * for for the number of channels and the sample rate of the current
+ * audio file.
+ *
+ * Buffer pools - An alternative to malloc/free buffer management.
+ *
+ * Non-leaf nodes usually create output to be processed by their children.  The
+ * data must be fed through the output channel(s) of the node in order to make
+ * that data available to each child.
+ *
+ * The easiest way to do so is to malloc() a buffer, fill it, and then call
+ * btr_add_output(). This adds references to that buffer to all children. The
+ * buffer is automatically freed if no buffer tree node is using it any more.
+ *
+ * This approach, while being simple, has some drawbacks, especially affecting
+ * the root nodes of the buffer tree. Often the data source which is
+ * represented by a root node does not know in advance how much data will be
+ * available.  Therefore the allocated buffer is either larger than what can
+ * currently be read, or is too small so that multiple buffers have to be used.
+ *
+ * While this could be worked around by using a large buffer and calling
+ * realloc() afterwards to shrink the buffer according to how much has been
+ * read, there is a second problem which comes from the alignment constraints
+ * of some filters, mainly the decoders like mp3dec. These need a minimal
+ * amount of data to proceed, and most of them even need this amount as one
+ * contiguous buffer, i.e. not spread out over two or more buffers.
+ *
+ * Although the buffer tree code handles this case just fine, it can be
+ * expensive because two or more buffers must be merged by copying buffer
+ * contents around in order to satisfy the constraint.
+ *
+ * This is where buffer pools come into play. Buffer pools try to satisfy
+ * alignment constraints without copying buffer content whenever possible. To
+ * avoid spreading out the input data over the address space like in the
+ * malloc/free approach, a fixed large contiguous buffer (the area) is used
+ * instead. A buffer pool consists basically of an area and two pointers, the
+ * read head and the write head.
+ *
+ * Once a buffer pool has been created, its node, e.g. a receiver, obtains the
+ * current value of the write head and writes new data to this location. Then
+ * it calls btr_add_output_pool() to tell much data it has written. This
+ * advances the write head accordingly, and it also creates references to the
+ * newly written part of the area for the children of the node to consume.
+ *
+ * Child nodes consume data by working through their input queue, which is a
+ * list of buffer references. Once the content of a buffer is no longer needed
+ * by a child node, the child calls btr_consume() to indicate the amount of
+ * data which can be dropped from the child's point of view. If no reference
+ * to some region of the buffer pool area remains, the read head of the buffer
+ * pool advances, making space available for the receiver node to fill.
+ *
+ * No matter if malloc() or a buffer pool is used, the buffer tree code takes
+ * care of alignment constraints imposed by the consumers. In the buffer pool
+ * case, automatic merging of references to contiguous buffers is performed.
+ * memcpy is only used if a constraint can not be satisfied by using the
+ * remaining part of the area only. This only happens when the end of the area
+ * is reached.
+ */

 
 struct btr_node;
 struct btr_pool;
 
 
 struct btr_node;
 struct btr_pool;
 

-typedef int (*btr_command_handler)(struct btr_node *btrn,
-               const char *command, char **result);
-
+/**
+ * The three different types of buffer tree nodes.
+ *
+ * Usually, there is exactly one node in the buffer tree, the root node, which
+ * has no parent. Every node different from the root node has exactly one
+ * parent.  The root node represents a data source. Root nodes are thus used by
+ * the receivers of paraslash. Also, reading from stdin is realized as the root
+ * node of a buffer tree.
+ *
+ * Each node may have arbitrary many children, including none. Nodes with no
+ * children are called leaf nodes. They represent a data sink, like the alsa or
+ * the file writer.
+ *
+ * Hence there are three different types of buffer tree nodes: The root node
+ * and the leaf nodes and nodes which have both a parent and at least one
+ * child. Such a node is called an internal node.
+ *
+ * Internal nodes represent filters through which data buffers flow, possibly
+ * while being altered on their way to the children of the node. Examples of
+ * internal nodes are audio file decoders (mp3dec, oggdec, ...), but also the
+ * check for a wav header is implemented as an internal buffer tree node.
+ */

 enum btr_node_type {
 enum btr_node_type {

+       /* This node has no parent. */

        BTR_NT_ROOT,
        BTR_NT_ROOT,

+       /* Node has parent and at least one child. */

        BTR_NT_INTERNAL,
        BTR_NT_INTERNAL,

+       /* Node has no children. */

        BTR_NT_LEAF,
 };
 
        BTR_NT_LEAF,
 };
 

-struct btr_pool *btr_pool_new(size_t area_size);
+/**
+ * Per node handler used for inter node communication.
+ *
+ * Each node in the buffer tree may optionally provide a command handler for
+ * execution of commands by other nodes of the tree.
+ *
+ * It is dependent on the node in question which commands are supported and how
+ * they work. In any case, the input for the command handler is some string and
+ * its output is also a string which is returned via the \a result pointer of
+ * the handler.
+ *
+ * This mechanism is used in para_audiod e.g. by the alsa writer which needs to
+ * know the sample rate of its input known to e.g. the mp3dec node further up
+ * in the buffer tree.
+ */
+typedef int (*btr_command_handler)(struct btr_node *btrn,
+               const char *command, char **result);
+
+/**
+ * Structure for creating new buffer tree nodes.
+ *
+ * btr_new_node() takes a pointer to such a structure.
+ *
+ * There are four different combinations of \a parent and child:
+ *
+ * 1. both \p NULL. This creates a new buffer tree with a single isolated node.
+ *
+ * 2. \a parent != \p NULL, \a child == NULL. This creates a new leaf node by
+ * adding the new node to the list of children of the given parent node.
+ *
+ * 3. \a parent == NULL, \a child != NULL. The new node becomes the new root of
+ * the buffer tree. The child must be old root.
+ *
+ * 4. both != NULL. This creates a new internal node. \a child must be child of
+ * p. This mode of operation is currently not needed and is thus not yet
+ * implemented.
+ */
+struct btr_node_description {
+       /** Name of the new node. */
+       const char *name;
+       /** Parent of the new node. */
+       struct btr_node *parent;
+       /** Child of the new node. */
+       struct btr_node *child;
+       /** Used for inter node communication. Optional. */
+       btr_command_handler handler;
+       /** Points usually to the struct that contains the node pointer. */
+       void *context;
+};
+
+size_t btr_pool_size(struct btr_pool *btrp);
+struct btr_pool *btr_pool_new(const char *name, size_t area_size);

 void btr_pool_free(struct btr_pool *btrp);
 size_t btr_pool_get_buffer(struct btr_pool *btrp, char **result);
 void btr_pool_free(struct btr_pool *btrp);
 size_t btr_pool_get_buffer(struct btr_pool *btrp, char **result);

-void btr_pool_allocate(struct btr_pool *btrp, size_t size);
-void btr_add_output_pool(struct btr_pool *btrp, char *buf, size_t size,
+int btr_pool_get_buffers(struct btr_pool *btrp, struct iovec iov[2]);
+void btr_add_output_pool(struct btr_pool *btrp, size_t size,
+       struct btr_node *btrn);
+size_t btr_pool_unused(struct btr_pool *btrp);
+void btr_copy(const void *src, size_t n, struct btr_pool *btrp,

        struct btr_node *btrn);
 
        struct btr_node *btrn);
 

-struct btr_node *btr_new_node(const char *name, struct btr_node *parent,
-               btr_command_handler handler, void *context);
+struct btr_node *btr_new_node(struct btr_node_description *bnd);

 void btr_remove_node(struct btr_node *btrn);
 void btr_free_node(struct btr_node *btrn);
 void btr_add_output(char *buf, size_t size, struct btr_node *btrn);
 void btr_remove_node(struct btr_node *btrn);
 void btr_free_node(struct btr_node *btrn);
 void btr_add_output(char *buf, size_t size, struct btr_node *btrn);

-bool btr_no_children(struct btr_node *btrn);
-size_t btr_bytes_pending(struct btr_node *btrn);

 size_t btr_get_input_queue_size(struct btr_node *btrn);
 size_t btr_get_input_queue_size(struct btr_node *btrn);

+size_t btr_get_output_queue_size(struct btr_node *btrn);

 bool btr_no_parent(struct btr_node *btrn);
 size_t btr_next_buffer(struct btr_node *btrn, char **bufp);
 bool btr_no_parent(struct btr_node *btrn);
 size_t btr_next_buffer(struct btr_node *btrn, char **bufp);

+size_t btr_next_buffer_omit(struct btr_node *btrn, size_t omit, char **bufp);

 void btr_consume(struct btr_node *btrn, size_t numbytes);
 void btr_consume(struct btr_node *btrn, size_t numbytes);

-int btr_exec(struct btr_node *btrn, const char *command, char **value_result);

 int btr_exec_up(struct btr_node *btrn, const char *command, char **value_result);
 void btr_splice_out_node(struct btr_node *btrn);
 void btr_pushdown(struct btr_node *btrn);
 void *btr_context(struct btr_node *btrn);
 void btr_merge(struct btr_node *btrn, size_t dest_size);
 int btr_exec_up(struct btr_node *btrn, const char *command, char **value_result);
 void btr_splice_out_node(struct btr_node *btrn);
 void btr_pushdown(struct btr_node *btrn);
 void *btr_context(struct btr_node *btrn);
 void btr_merge(struct btr_node *btrn, size_t dest_size);

-bool btr_eof(struct btr_node *btrn);

 void btr_log_tree(struct btr_node *btrn, int loglevel);
 void btr_log_tree(struct btr_node *btrn, int loglevel);

-int btr_pushdown_one(struct btr_node *btrn);
+void btr_pushdown_one(struct btr_node *btrn);

 bool btr_inplace_ok(struct btr_node *btrn);
 int btr_node_status(struct btr_node *btrn, size_t min_iqs,
                enum btr_node_type type);
 void btr_get_node_start(struct btr_node *btrn, struct timeval *tv);
 bool btr_inplace_ok(struct btr_node *btrn);
 int btr_node_status(struct btr_node *btrn, size_t min_iqs,
                enum btr_node_type type);
 void btr_get_node_start(struct btr_node *btrn, struct timeval *tv);

+struct btr_node *btr_search_node(const char *name, struct btr_node *root);
+void btr_drain(struct btr_node *btrn);