diff options
Diffstat (limited to 'erts/doc/src/erl_nif.xml')
| -rw-r--r-- | erts/doc/src/erl_nif.xml | 284 |
1 files changed, 279 insertions, 5 deletions
diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml index 5a69bed34c..419e41693e 100644 --- a/erts/doc/src/erl_nif.xml +++ b/erts/doc/src/erl_nif.xml @@ -206,7 +206,7 @@ ok <seealso marker="#enif_make_resource"> <c>enif_make_resource</c></seealso>. The term returned by <c>enif_make_resource</c> is opaque in nature. - It can be stored and passed between processes on the same node, but + It can be stored and passed between processes, but the only real end usage is to pass it back as an argument to a NIF. The NIF can then call <seealso marker="#enif_get_resource"> <c>enif_get_resource</c></seealso> and get back a pointer to the @@ -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, &tail, &iovec); + +/* Use a stack-allocated vector as an optimization for vectors with few elements */ +ErlNifIOVec vec, *iovec = &vec; +enif_inspect_iovec(env, max_elements, term, &tail, &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> @@ -1952,10 +2203,33 @@ typedef enum { details, see the <seealso marker="#enif_resource_example">example of creating and returning a resource object</seealso> in the User's Guide.</p> - <p>Notice that the only defined behavior of using a resource term in - an Erlang program is to store it and send it between processes on the - same node. Other operations, such as matching or - <c>term_to_binary</c>, have unpredictable (but harmless) results.</p> + <note> + <p>Since ERTS 9.0 (OTP-20.0), resource terms have a defined behavior + when compared and serialized through <c>term_to_binary</c> or passed + between nodes.</p> + <list type="bulleted"> + <item> + <p>Two resource terms will compare equal iff they + would yield the same resource object pointer when passed to + <seealso marker="#enif_get_resource"><c>enif_get_resource</c></seealso>.</p> + </item> + <item> + <p>A resoure term can be serialized with <c>term_to_binary</c> and later + be fully recreated if the resource object is still alive when + <c>binary_to_term</c> is called. A <em>stale</em> resource term will be + returned from <c>binary_to_term</c> if the resource object has + been deallocated. <seealso marker="#enif_get_resource"><c>enif_get_resource</c></seealso> + will return false for stale resource terms.</p> + <p>The same principles of serialization apply when passing + resource terms in messages to remote nodes and back again. A + resource term will act stale on all nodes except the node where + its resource object is still alive in memory.</p> + </item> + </list> + <p>Before ERTS 9.0 (OTP-20.0), all resource terms did + compare equal to each other and to empty binaries (<c><<>></c>). + If serialized, they would be recreated as plain empty binaries.</p> + </note> </desc> </func> |