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diff --git a/system/doc/tutorial/erl_interface.xmlsrc b/system/doc/tutorial/erl_interface.xmlsrc index 0c4c5a99c2..5751a945d6 100644 --- a/system/doc/tutorial/erl_interface.xmlsrc +++ b/system/doc/tutorial/erl_interface.xmlsrc @@ -4,7 +4,7 @@ <chapter> <header> <copyright> - <year>2000</year><year>2013</year> + <year>2000</year><year>2015</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -28,14 +28,29 @@ <rev></rev> <file>erl_interface.xml</file> </header> - <p>This is an example of how to solve the <seealso marker="example">example problem</seealso> by using a port and <c>erl_interface</c>. It is necessary to read the <seealso marker="c_port">port example</seealso> before reading this chapter.</p> + + <p>This section outlines an example of how to solve the example + problem in <seealso marker="example">Problem Example</seealso> by + using a port and Erl_Interface. It is necessary to read the port + example in <seealso marker="c_port">Ports</seealso> before reading + this section.</p> <section> <title>Erlang Program</title> - <p>The example below shows an Erlang program communicating with a C program over a plain port with home made encoding.</p> - <codeinclude file="complex1.erl" type="erl"/> - <p>Compared to the Erlang module - above used for the plain port, there are two differences when using Erl_Interface on the C side: Since Erl_Interface operates on the Erlang external term format the port must be set to use binaries and, instead of inventing an encoding/decoding scheme, the BIFs <c>term_to_binary/1</c> and <c>binary_to_term/1</c> should be used. That is:</p> + <p>The following example shows an Erlang program communicating + with a C program over a plain port with home made encoding:</p> + <codeinclude file="complex1.erl" type="erl"/> + <p>There are two differences when using Erl_Interface on the C + side compared to the example in <seealso marker="c_port"> + Ports</seealso>, using only the plain port:</p> + <list type="bulleted"> + <item>As Erl_Interface operates on the Erlang external term format, + the port must be set to use binaries.</item> + <item>Instead of inventing an encoding/decoding scheme, the + <c>term_to_binary/1</c> and <c>binary_to_term/1</c> BIFs are to + be used.</item> + </list> + <p>That is:</p> <pre> open_port({spawn, ExtPrg}, [{packet, 2}])</pre> <p>is replaced with:</p> @@ -55,69 +70,110 @@ receive {Port, {data, Data}} -> Caller ! {complex, binary_to_term(Data)} end</pre> - <p>The resulting Erlang program is shown below.</p> + <p>The resulting Erlang program is as follows:</p> <codeinclude file="complex2.erl" type="erl"/> - <p>Note that calling <c>complex2:foo/1</c> and <c>complex2:bar/1</c> will result in the tuple <c>{foo,X}</c> or <c>{bar,Y}</c> being sent to the <c>complex</c> process, which will code them as binaries and send them to the port. This means that the C program must be able to handle these two tuples.</p> + <p>Notice that calling <c>complex2:foo/1</c> and + <c>complex2:bar/1</c> results in the tuple <c>{foo,X}</c> or + <c>{bar,Y}</c> being sent to the <c>complex</c> process, which + codes them as binaries and sends them to the port. This means + that the C program must be able to handle these two tuples.</p> </section> <section> <title>C Program</title> - <p>The example below shows a C program communicating with an Erlang program over a plain port with home made encoding.</p> + <p>The following example shows a C program communicating with an + Erlang program over a plain port with home made encoding:</p> <codeinclude file="port.c" type="c"/> - <p>Compared to the C program above - used for the plain port the <c>while</c>-loop must be rewritten. Messages coming from the port will be on the Erlang external term format. They should be converted into an <c>ETERM</c> struct, a C struct similar to an Erlang term. The result of calling <c>foo()</c> or <c>bar()</c> must be converted to the Erlang external term format before being sent back to the port. But before calling any other <c>erl_interface</c> function, the memory handling must be initiated.</p> + <p>Compared to the C program in <seealso marker="c_port"> + Ports</seealso>, using only the plain port, the + <c>while</c>-loop must be rewritten. Messages coming from the + port is on the Erlang external term format. They must be + converted into an <c>ETERM</c> struct, which is a C struct + similar to an Erlang term. The result of calling <c>foo()</c> or + <c>bar()</c> must be converted to the Erlang external term + format before being sent back to the port. But before calling + any other Erl_Interface function, the memory handling must be + initiated:</p> <pre> erl_init(NULL, 0);</pre> - <p>For reading from and writing to the port the functions <c>read_cmd()</c> and <c>write_cmd()</c> from the erl_comm.c example below - can still be used. + <p>The following functions, <c>read_cmd()</c> and + <c>write_cmd()</c>, from the <c>erl_comm.c</c> example in + <seealso marker="c_port">Ports</seealso> can still be + used for reading from and writing to the port: </p> <codeinclude file="erl_comm.c" type="c"/> - <p>The function <c>erl_decode()</c> from <c>erl_marshal</c> will convert the binary into an <c>ETERM</c> struct.</p> + <p>The function <c>erl_decode()</c> from <c>erl_marshal</c> + converts the binary into an <c>ETERM</c> struct:</p> <pre> int main() { ETERM *tuplep; while (read_cmd(buf) > 0) { tuplep = erl_decode(buf);</pre> - <p>In this case <c>tuplep</c> now points to an <c>ETERM</c> struct representing a tuple with two elements; the function name (atom) and the argument (integer). By using the function <c>erl_element()</c> from <c>erl_eterm</c> it is possible to extract these elements, which also must be declared as pointers to an <c>ETERM</c> struct.</p> + <p>Here, <c>tuplep</c> points to an <c>ETERM</c> struct + representing a tuple with two elements; the function name (atom) + and the argument (integer). Using the function + <c>erl_element()</c> from <c>erl_eterm</c>, these elements can + be extracted, but they must also be declared as pointers to an + <c>ETERM</c> struct:</p> <pre> fnp = erl_element(1, tuplep); argp = erl_element(2, tuplep);</pre> - <p>The macros <c>ERL_ATOM_PTR</c> and <c>ERL_INT_VALUE</c> from <c>erl_eterm</c> can be used to obtain the actual values of the atom and the integer. The atom value is represented as a string. By comparing this value with the strings "foo" and "bar" it can be decided which function to call.</p> + <p>The macros <c>ERL_ATOM_PTR</c> and <c>ERL_INT_VALUE</c> from + <c>erl_eterm</c> can be used to obtain the actual values of the + atom and the integer. The atom value is represented as a string. + By comparing this value with the strings "foo" and "bar", it can + be decided which function to call:</p> <pre> if (strncmp(ERL_ATOM_PTR(fnp), "foo", 3) == 0) { res = foo(ERL_INT_VALUE(argp)); } else if (strncmp(ERL_ATOM_PTR(fnp), "bar", 3) == 0) { res = bar(ERL_INT_VALUE(argp)); }</pre> - <p>Now an <c>ETERM</c> struct representing the integer result can be constructed using the function <c>erl_mk_int()</c> from <c>erl_eterm</c>. It is also possible to use the function <c>erl_format()</c> from the module <c>erl_format</c>.</p> + <p>Now an <c>ETERM</c> struct that represents the integer result + can be constructed using the function <c>erl_mk_int()</c> from + <c>erl_eterm</c>. The function + <c>erl_format()</c> from the module <c>erl_format</c> can also + be used:</p> <pre> intp = erl_mk_int(res);</pre> - <p>The resulting <c>ETERM</c> struct is converted into the Erlang external term format using the function <c>erl_encode()</c> from <c>erl_marshal</c> and sent to Erlang using <c>write_cmd()</c>.</p> + <p>The resulting <c>ETERM</c> struct is converted into the Erlang + external term format using the function <c>erl_encode()</c> from + <c>erl_marshal</c> and sent to Erlang using + <c>write_cmd()</c>:</p> <pre> erl_encode(intp, buf); write_cmd(buf, erl_eterm_len(intp));</pre> - <p>Last, the memory allocated by the <c>ETERM</c> creating functions must be freed.</p> + <p>Finally, the memory allocated by the <c>ETERM</c> creating + functions must be freed:</p> <pre> erl_free_compound(tuplep); erl_free_term(fnp); erl_free_term(argp); erl_free_term(intp);</pre> - <p>The resulting C program is shown below:</p> + <p>The resulting C program is as follows:</p> <codeinclude file="ei.c" type="c"/> </section> <section> <title>Running the Example</title> - <p>1. Compile the C code, providing the paths to the include files <c>erl_interface.h</c> and <c>ei.h</c>, and to the libraries <c>erl_interface</c> and <c>ei</c>.</p> + <p><em>Step 1.</em> Compile the C code. This provides the paths to + the include files <c>erl_interface.h</c> and <c>ei.h</c>, and + also to the libraries <c>erl_interface</c> and <c>ei</c>:</p> <pre> unix> <input>gcc -o extprg -I/usr/local/otp/lib/erl_interface-3.2.1/include \\ </input> <input> -L/usr/local/otp/lib/erl_interface-3.2.1/lib \\ </input> <input> complex.c erl_comm.c ei.c -lerl_interface -lei</input></pre> - <p>In R5B and later versions of OTP, the <c>include</c> and <c>lib</c> directories are situated under <c>OTPROOT/lib/erl_interface-VSN</c>, where <c>OTPROOT</c> is the root directory of the OTP installation (<c>/usr/local/otp</c> in the example above) and <c>VSN</c> is the version of the <c>erl_interface</c> application (3.2.1 in the example above). <br></br> - - In R4B and earlier versions of OTP, <c>include</c> and <c>lib</c> are situated under <c>OTPROOT/usr</c>.</p> - <p>2. Start Erlang and compile the Erlang code.</p> + <p>In Erlang/OTP R5B and later versions of OTP, the <c>include</c> + and <c>lib</c> directories are situated under + <c>OTPROOT/lib/erl_interface-VSN</c>, where <c>OTPROOT</c> is + the root directory of the OTP installation + (<c>/usr/local/otp</c> in the recent example) and <c>VSN</c> is + the version of the Erl_interface application (3.2.1 in the + recent example).</p> + <p>In R4B and earlier versions of OTP, <c>include</c> and <c>lib</c> + are situated under <c>OTPROOT/usr</c>.</p> + <p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p> <pre> unix> <input>erl</input> Erlang (BEAM) emulator version 4.9.1.2 @@ -125,7 +181,7 @@ Erlang (BEAM) emulator version 4.9.1.2 Eshell V4.9.1.2 (abort with ^G) 1> <input>c(complex2).</input> {ok,complex2}</pre> - <p>3. Run the example.</p> + <p><em>Step 3.</em> Run the example:</p> <pre> 2> <input>complex2:start("extprg").</input> <0.34.0> |