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authorLukas Larsson <[email protected]>2017-02-24 19:38:37 +0100
committerLukas Larsson <[email protected]>2017-09-05 14:35:26 +0200
commit314702f86c9199957e40edfb73bcdbddb422f9d7 (patch)
tree08421d1740b23964f62eaefa74321528897bb06a /erts/doc/src/erl_nif.xml
parent520310feef0d76c0f99447187f3574408b219ae5 (diff)
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erts: Add nif ioq
Diffstat (limited to 'erts/doc/src/erl_nif.xml')
-rw-r--r--erts/doc/src/erl_nif.xml251
1 files changed, 251 insertions, 0 deletions
diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index 5a69bed34c..e47bb6a806 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -344,6 +344,81 @@ return term;</code>
<c>enif_convert_time_unit()</c></seealso></item>
</list>
</item>
+ <tag><marker id="enif_ioq"/>I/O Queues</tag>
+ <item>
+ <p>The Erlang nif library contains function for easily working
+ with I/O vectors as used by the unix system call <c>writev</c>.
+ The I/O Queue is not thread safe, so some other synchronization
+ mechanism has to be used.</p>
+ <list type="bulleted">
+ <item><seealso marker="#SysIOVec">
+ <c>SysIOVec</c></seealso></item>
+ <item><seealso marker="#ErlNifIOVec">
+ <c>ErlNifIOVec</c></seealso></item>
+ <item><seealso marker="#enif_ioq_create">
+ <c>enif_ioq_create()</c></seealso></item>
+ <item><seealso marker="#enif_ioq_destroy">
+ <c>enif_ioq_destroy()</c></seealso></item>
+ <item><seealso marker="#enif_ioq_enq_binary">
+ <c>enif_ioq_enq_binary()</c></seealso></item>
+ <item><seealso marker="#enif_ioq_enqv">
+ <c>enif_ioq_enqv()</c></seealso></item>
+ <item><seealso marker="#enif_ioq_deq">
+ <c>enif_ioq_deq()</c></seealso></item>
+ <item><seealso marker="#enif_ioq_peek">
+ <c>enif_ioq_peek()</c></seealso></item>
+ <item><seealso marker="#enif_inspect_iovec">
+ <c>enif_inspect_iovec()</c></seealso></item>
+ <item><seealso marker="#enif_free_iovec">
+ <c>enif_free_iovec()</c></seealso></item>
+ </list>
+ <p>Typical usage when writing to a file descriptor looks like this:</p>
+ <code type="none"><![CDATA[
+int writeiovec(ErlNifEnv *env, ERL_NIF_TERM term, ERL_NIF_TERM *tail,
+ ErlNifIOQueue *q, int fd) {
+
+ ErlNifIOVec vec, *iovec = &vec;
+ SysIOVec *sysiovec;
+ int saved_errno;
+ int iovcnt, n;
+
+ if (!enif_inspect_iovec(env, 64, term, tail, &iovec))
+ return -2;
+
+ if (enif_ioq_size(q) > 0) {
+ /* If the I/O queue contains data we enqueue the iovec and
+ then peek the data to write out of the queue. */
+ if (!enif_ioq_enqv(q, iovec, 0))
+ return -3;
+
+ sysiovec = enif_ioq_peek(q, &iovcnt);
+ } else {
+ /* If the I/O queue is empty we skip the trip through it. */
+ iovcnt = iovec->iovcnt;
+ sysiovec = iovec->iov;
+ }
+
+ /* Attempt to write the data */
+ n = writev(fd, sysiovec, iovcnt);
+ saved_errno = errno;
+
+ if (enif_ioq_size(q) == 0) {
+ /* If the I/O queue was initially empty we enqueue any
+ remaining data into the queue for writing later. */
+ if (n >= 0 && !enif_ioq_enqv(q, iovec, n))
+ return -3;
+ } else {
+ /* Dequeue any data that was written from the queue. */
+ if (n > 0 && !enif_ioq_deq(q, n, NULL))
+ return -4;
+ }
+
+ /* return n, which is either number of bytes written or -1 if
+ some error happened */
+ errno = saved_errno;
+ return n;
+}]]></code>
+ </item>
<tag><marker id="lengthy_work"/>Long-running NIFs</tag>
<item>
<p>As mentioned in the <seealso marker="#WARNING">warning</seealso> text
@@ -837,6 +912,36 @@ typedef enum {
</item>
</taglist>
</item>
+ <tag><marker id="SysIOVec"/><c>SysIOVec</c></tag>
+ <item>
+ <p>A system I/O vector, as used by <c>writev</c> on
+ Unix and <c>WSASend</c> on Win32. It is used in
+ <c>ErlNifIOVec</c> and by
+ <seealso marker="#enif_ioq_peek"><c>enif_ioq_peek</c></seealso>.</p>
+ </item>
+ <tag><marker id="ErlNifIOVec"/><c>ErlNifIOVec</c></tag>
+ <item>
+ <code type="none">
+typedef struct {
+ int iovcnt;
+ size_t size;
+ SysIOVec* iov;
+} ErlNifIOVec;</code>
+ <p>An I/O vector containing <c>iovcnt</c> <c>SysIOVec</c>s
+ pointing to the data. It is used by
+ <seealso marker="#enif_inspect_iovec">
+ <c>enif_inspect_iovec</c></seealso> and
+ <seealso marker="#enif_ioq_enqv">
+ <c>enif_ioq_enqv</c></seealso>.</p>
+ </item>
+ <tag><marker id="ErlNifIOQueueOpts"/><c>ErlNifIOQueueOpts</c></tag>
+ <item>
+ Options to configure a <c>ErlNifIOQueue</c>.
+ <taglist>
+ <tag>ERL_NIF_IOQ_NORMAL</tag>
+ <item><p>Create a normal I/O Queue</p></item>
+ </taglist>
+ </item>
</taglist>
</section>
@@ -1143,6 +1248,31 @@ typedef enum {
</func>
<func>
+ <name><ret>void</ret>
+ <nametext>enif_free_iovec(ErlNifIOvec* iov)</nametext></name>
+ <fsummary>Free an ErlIOVec</fsummary>
+ <desc>
+ <p>Frees an io vector returned from
+ <seealso marker="#enif_inspect_iovec">
+ <c>enif_inspect_iovec</c></seealso>.
+ This is needed only if a <c>NULL</c> environment is passed to
+ <seealso marker="#enif_inspect_iovec">
+ <c>enif_inspect_iovec</c></seealso>.</p>
+ <code type="none"><![CDATA[
+ErlNifIOVec *iovec = NULL;
+size_t max_elements = 128;
+ERL_NIF_TERM tail;
+if (!enif_inspect_iovec(NULL, max_elements, term, &tail, iovec))
+ return 0;
+
+// Do things with the iovec
+
+/* Free the iovector, possibly in another thread or nif function call */
+enif_free_iovec(iovec);]]></code>
+ </desc>
+ </func>
+
+ <func>
<name><ret>int</ret><nametext>enif_get_atom(ErlNifEnv* env, ERL_NIF_TERM
term, char* buf, unsigned size, ErlNifCharEncoding encode)</nametext>
</name>
@@ -1449,6 +1579,127 @@ typedef enum {
</func>
<func>
+ <name><ret>int</ret><nametext>enif_inspect_iovec(ErlNifEnv*
+ env, size_t max_elements, ERL_NIF_TERM iovec_term, ERL_NIF_TERM* tail,
+ ErlNifIOVec** iovec)</nametext></name>
+ <fsummary>Inspect a list of binaries as an ErlNifIOVec.</fsummary>
+ <desc>
+ <p>Fills <c>iovec</c> with the list of binaries provided in
+ <c>iovec_term</c>. The number of elements handled in the call is
+ limited to <c>max_elements</c>, and <c>tail</c> is set to the
+ remainder of the list. Note that the output may be longer than
+ <c>max_elements</c> on some platforms.
+ </p>
+ <p>To create a list of binaries from an arbitrary iolist, use
+ <seealso marker="erts:erlang#iolist_to_iovec/1">
+ <c>erlang:iolist_to_iovec/1</c></seealso>.</p>
+ <p>When calling this function, <c>iovec</c> should contain a pointer to
+ <c>NULL</c> or a ErlNifIOVec structure that should be used if
+ possible. e.g.
+ </p>
+ <code type="none">
+/* Don't use a pre-allocated structure */
+ErlNifIOVec *iovec = NULL;
+enif_inspect_iovec(env, max_elements, term, &amp;tail, &amp;iovec);
+
+/* Use a stack-allocated vector as an optimization for vectors with few elements */
+ErlNifIOVec vec, *iovec = &amp;vec;
+enif_inspect_iovec(env, max_elements, term, &amp;tail, &amp;iovec);
+</code>
+ <p>The contents of the <c>iovec</c> is valid until the called nif
+ function returns. If the <c>iovec</c> should be valid after the nif
+ call returns, it is possible to call this function with a
+ <c>NULL</c> environment. If no environment is given the <c>iovec</c>
+ owns the data in the vector and it has to be explicitly freed using
+ <seealso marker="#enif_free_iovec"><c>enif_free_iovec</c>
+ </seealso>.</p>
+ <p>Returns <c>true</c> on success, or <c>false</c> if <c>iovec_term</c>
+ not an iovec.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>ErlNifIOQueue *</ret>
+ <nametext>enif_ioq_create(ErlNifIOQueueOpts opts)</nametext></name>
+ <fsummary>Create a new IO Queue</fsummary>
+ <desc>
+ <p>Create a new I/O Queue that can be used to store data.
+ <c>opts</c> has to be set to <c>ERL_NIF_IOQ_NORMAL</c>.
+ </p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>void</ret>
+ <nametext>enif_ioq_destroy(ErlNifIOQueue *q)</nametext></name>
+ <fsummary>Destroy an IO Queue and free it's content</fsummary>
+ <desc>
+ <p>Destroy the I/O queue and free all of it's contents</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>int</ret>
+ <nametext>enif_ioq_deq(ErlNifIOQueue *q, size_t count, size_t *size)</nametext></name>
+ <fsummary>Dequeue count bytes from the IO Queue</fsummary>
+ <desc>
+ <p>Dequeue <c>count</c> bytes from the I/O queue.
+ If <c>size</c> is not <c>NULL</c>, the new size of the queue
+ is placed there.</p>
+ <p>Returns <c>true</c> on success, or <c>false</c> if the I/O does
+ not contain <c>count</c> bytes. On failure the queue is left un-altered.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>int</ret>
+ <nametext>enif_ioq_enq_binary(ErlNifIOQueue *q, ErlNifBinary *bin, size_t skip)</nametext></name>
+ <fsummary>Enqueue the binary into the IO Queue</fsummary>
+ <desc>
+ <p>Enqueue the <c>bin</c> into <c>q</c> skipping the first <c>skip</c> bytes.</p>
+ <p>Returns <c>true</c> on success, or <c>false</c> if <c>skip</c> is greater
+ than the size of <c>bin</c>. Any ownership of the binary data is transferred
+ to the queue and <c>bin</c> is to be considered read-only for the rest of the NIF
+ call and then as released.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>int</ret>
+ <nametext>enif_ioq_enqv(ErlNifIOQueue *q, ErlNifIOVec *iovec, size_t skip)</nametext></name>
+ <fsummary>Enqueue the iovec into the IO Queue</fsummary>
+ <desc>
+ <p>Enqueue the <c>iovec</c> into <c>q</c> skipping the first <c>skip</c> bytes.</p>
+ <p>Returns <c>true</c> on success, or <c>false</c> if <c>skip</c> is greater
+ than the size of <c>iovec</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>SysIOVec *</ret>
+ <nametext>enif_ioq_peek(ErlNifIOQueue *q, int *iovlen)</nametext></name>
+ <fsummary>Peek inside the IO Queue</fsummary>
+ <desc>
+ <p>Get the I/O queue as a pointer to an array of <c>SysIOVec</c>s.
+ It also returns the number of elements in <c>iovlen</c>.
+ This is the only way to get data out of the queue.</p>
+ <p>Nothing is removed from the queue by this function, that must be done
+ with <seealso marker="#enif_ioq_deq"><c>enif_ioq_deq</c></seealso>.</p>
+ <p>The returned array is suitable to use with the Unix system
+ call <c>writev</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name><ret>size_t</ret>
+ <nametext>enif_ioq_size(ErlNifIOQueue *q)</nametext></name>
+ <fsummary>Get the current size of the IO Queue</fsummary>
+ <desc>
+ <p>Get the size of <c>q</c>.</p>
+ </desc>
+ </func>
+
+ <func>
<name><ret>int</ret>
<nametext>enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
</name>