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diff --git a/lib/stdlib/doc/src/file_sorter.xml b/lib/stdlib/doc/src/file_sorter.xml index bc24f02a99..e988d58c2f 100644 --- a/lib/stdlib/doc/src/file_sorter.xml +++ b/lib/stdlib/doc/src/file_sorter.xml @@ -24,125 +24,150 @@ <title>file_sorter</title> <prepared>Hans Bolinder</prepared> - <responsible>nobody</responsible> + <responsible></responsible> <docno></docno> - <approved>nobody</approved> - <checked>no</checked> + <approved></approved> + <checked></checked> <date>2001-03-13</date> <rev>PA1</rev> - <file>file_sorter.sgml</file> + <file>file_sorter.xml</file> </header> <module>file_sorter</module> - <modulesummary>File Sorter</modulesummary> + <modulesummary>File sorter.</modulesummary> <description> - <p>The functions of this module sort terms on files, merge already - sorted files, and check files for sortedness. Chunks containing - binary terms are read from a sequence of files, sorted + <p>This module contains functions for sorting terms on files, merging + already sorted files, and checking files for sortedness. Chunks + containing binary terms are read from a sequence of files, sorted internally in memory and written on temporary files, which are merged producing one sorted file as output. Merging is provided as an optimization; it is faster when the files are already - sorted, but it always works to sort instead of merge. - </p> + sorted, but it always works to sort instead of merge.</p> + <p>On a file, a term is represented by a header and a binary. Two - options define the format of terms on files: - </p> - <list type="bulleted"> - <item><c>{header, HeaderLength}</c>. HeaderLength determines the - number of bytes preceding each binary and containing the - length of the binary in bytes. Default is 4. The order of the - header bytes is defined as follows: if <c>B</c> is a binary - containing a header only, the size <c>Size</c> of the binary - is calculated as - <c><![CDATA[<<Size:HeaderLength/unit:8>> = B]]></c>. + options define the format of terms on files:</p> + + <taglist> + <tag><c>{header, HeaderLength}</c></tag> + <item> + <p><c>HeaderLength</c> determines the + number of bytes preceding each binary and containing the + length of the binary in bytes. Defaults to 4. The order of the + header bytes is defined as follows: if <c>B</c> is a binary + containing a header only, size <c>Size</c> of the binary + is calculated as + <c><![CDATA[<<Size:HeaderLength/unit:8>> = B]]></c>.</p> </item> - <item><c>{format, Format}</c>. The format determines the - function that is applied to binaries in order to create the - terms that will be sorted. The default value is - <c>binary_term</c>, which is equivalent to - <c>fun binary_to_term/1</c>. The value <c>binary</c> is - equivalent to <c>fun(X) -> X end</c>, which means that the - binaries will be sorted as they are. This is the fastest - format. If <c>Format</c> is <c>term</c>, <c>io:read/2</c> is - called to read terms. In that case only the default value of - the <c>header</c> option is allowed. The <c>format</c> option - also determines what is written to the sorted output file: if - <c>Format</c> is <c>term</c> then <c>io:format/3</c> is called - to write each term, otherwise the binary prefixed by a header - is written. Note that the binary written is the same binary - that was read; the results of applying the <c>Format</c> - function are thrown away as soon as the terms have been - sorted. Reading and writing terms using the <c>io</c> module - is very much slower than reading and writing binaries. + <tag><c>{format, Format}</c></tag> + <item> + <p>Option <c>Format</c> determines the + function that is applied to binaries to create the + terms to be sorted. Defaults to + <c>binary_term</c>, which is equivalent to + <c>fun binary_to_term/1</c>. Value <c>binary</c> is + equivalent to <c>fun(X) -> X end</c>, which means that the + binaries are sorted as they are. This is the fastest + format. If <c>Format</c> is <c>term</c>, <c>io:read/2</c> is + called to read terms. In that case, only the default value of + option <c>header</c> is allowed.</p> + <p>Option <c>format</c> also determines what is written to the + sorted output file: if + <c>Format</c> is <c>term</c>, then <c>io:format/3</c> is called + to write each term, otherwise the binary prefixed by a header + is written. Notice that the binary written is the same binary + that was read; the results of applying function <c>Format</c> + are thrown away when the terms have been sorted. + Reading and writing terms using the <c>io</c> module + is much slower than reading and writing binaries.</p> </item> - </list> - <p>Other options are: - </p> - <list type="bulleted"> - <item><c>{order, Order}</c>. The default is to sort terms in - ascending order, but that can be changed by the value - <c>descending</c> or by giving an ordering function <c>Fun</c>. - An ordering function is antisymmetric, transitive and total. - <c>Fun(A, B)</c> should return <c>true</c> if <c>A</c> - comes before <c>B</c> in the ordering, <c>false</c> otherwise. - An example of a typical ordering function is less than or equal - to, <c>=</2</c>. - Using an ordering function will slow down the sort - considerably. The <c>keysort</c>, <c>keymerge</c> and - <c>keycheck</c> functions do not accept ordering functions. + </taglist> + + <p>Other options are:</p> + + <taglist> + <tag><c>{order, Order}</c></tag> + <item> + <p>The default is to sort terms in + ascending order, but that can be changed by value + <c>descending</c> or by specifying an ordering function <c>Fun</c>. + An ordering function is antisymmetric, transitive, and total. + <c>Fun(A, B)</c> is to return <c>true</c> if <c>A</c> + comes before <c>B</c> in the ordering, otherwise <c>false</c>. + An example of a typical ordering function is less than or equal + to, <c>=</2</c>. Using an ordering function slows down the sort + considerably. Functions <c>keysort</c>, <c>keymerge</c> and + <c>keycheck</c> do not accept ordering functions.</p> </item> - <item><c>{unique, boolean()}</c>. When sorting or merging files, - only the first of a sequence of terms that compare equal (<c>==</c>) - is output if this option is set to <c>true</c>. The default - value is <c>false</c> which implies that all terms that - compare equal are output. When checking files for - sortedness, a check that no pair of consecutive terms - compares equal is done if this option is set to <c>true</c>. + <tag><c>{unique, boolean()}</c></tag> + <item> + <p>When sorting or merging files, + only the first of a sequence of terms that compare equal (<c>==</c>) + is output if this option is set to <c>true</c>. Defaults + to <c>false</c>, which implies that all terms that + compare equal are output. When checking files for + sortedness, a check that no pair of consecutive terms + compares equal is done if this option is set to <c>true</c>.</p> </item> - <item><c>{tmpdir, TempDirectory}</c>. The directory where - temporary files are put can be chosen explicitly. The - default, implied by the value <c>""</c>, is to put temporary - files on the same directory as the sorted output file. If - output is a function (see below), the directory returned by - <c>file:get_cwd()</c> is used instead. The names of - temporary files are derived from the Erlang nodename - (<c>node()</c>), the process identifier of the current Erlang - emulator (<c>os:getpid()</c>), and a unique integer - (<c>erlang:unique_integer([positive])</c>); a typical name would be - <c>fs_mynode@myhost_1763_4711.17</c>, where - <c>17</c> is a sequence number. Existing files will be - overwritten. Temporary files are deleted unless some - uncaught EXIT signal occurs. + <tag><c>{tmpdir, TempDirectory}</c></tag> + <item> + <p>The directory where + temporary files are put can be chosen explicitly. The + default, implied by value <c>""</c>, is to put temporary + files on the same directory as the sorted output file. If + output is a function (see below), the directory returned by + <c>file:get_cwd()</c> is used instead. The names of + temporary files are derived from the Erlang nodename + (<c>node()</c>), the process identifier of the current Erlang + emulator (<c>os:getpid()</c>), and a unique integer + (<c>erlang:unique_integer([positive])</c>). A typical name is + <c>fs_mynode@myhost_1763_4711.17</c>, where + <c>17</c> is a sequence number. Existing files are + overwritten. Temporary files are deleted unless some + uncaught <c>EXIT</c> signal occurs.</p> </item> - <item><c>{compressed, boolean()}</c>. Temporary files and the - output file may be compressed. The default value - <c>false</c> implies that written files are not - compressed. Regardless of the value of the <c>compressed</c> - option, compressed files can always be read. Note that - reading and writing compressed files is significantly slower - than reading and writing uncompressed files. + <tag><c>{compressed, boolean()}</c></tag> + <item> + <p>Temporary files and the output file can be compressed. Defaults + <c>false</c>, which implies that written files are not + compressed. Regardless of the value of option <c>compressed</c>, + compressed files can always be read. Notice that + reading and writing compressed files are significantly slower + than reading and writing uncompressed files.</p> </item> - <item><c>{size, Size}</c>. By default approximately 512*1024 - bytes read from files are sorted internally. This option - should rarely be needed. + <tag><c>{size, Size}</c></tag> + <item> + <p>By default about 512*1024 bytes read from files are sorted + internally. This option is rarely needed.</p> </item> - <item><c>{no_files, NoFiles}</c>. By default 16 files are - merged at a time. This option should rarely be needed. + <tag><c>{no_files, NoFiles}</c></tag> + <item> + <p>By default 16 files are merged at a time. This option is rarely + needed.</p> </item> - </list> + </taglist> + <p>As an alternative to sorting files, a function of one argument - can be given as input. When called with the argument <c>read</c> - the function is assumed to return <c>end_of_input</c> or - <c>{end_of_input, Value}}</c> when there is no more input - (<c>Value</c> is explained below), or <c>{Objects, Fun}</c>, - where <c>Objects</c> is a list of binaries or terms depending on - the format and <c>Fun</c> is a new input function. Any other - value is immediately returned as value of the current call to - <c>sort</c> or <c>keysort</c>. Each input function will be - called exactly once, and should an error occur, the last - function is called with the argument <c>close</c>, the reply of - which is ignored. - </p> - <p>A function of one argument can be given as output. The results + can be specified as input. When called with argument <c>read</c>, + the function is assumed to return either of the following:</p> + + <list type="bulleted"> + <item> + <p><c>end_of_input</c> or <c>{end_of_input, Value}}</c> when there + is no more input (<c>Value</c> is explained below).</p> + </item> + <item> + <p><c>{Objects, Fun}</c>, where <c>Objects</c> is a list of binaries + or terms depending on the format, and <c>Fun</c> is a new input + function.</p> + </item> + </list> + + <p>Any other value is immediately returned as value of the current call + to <c>sort</c> or <c>keysort</c>. Each input function is + called exactly once. If an error occurs, the last + function is called with argument <c>close</c>, the reply of + which is ignored.</p> + + <p>A function of one argument can be specified as output. The results of sorting or merging the input is collected in a non-empty sequence of variable length lists of binaries or terms depending on the format. The output function is called with one list at a @@ -151,18 +176,20 @@ call to the sort or merge function. Each output function is called exactly once. When some output function has been applied to all of the results or an error occurs, the last function is - called with the argument <c>close</c>, and the reply is returned - as value of the current call to the sort or merge function. If a - function is given as input and the last input function returns - <c>{end_of_input, Value}</c>, the function given as output will - be called with the argument <c>{value, Value}</c>. This makes it + called with argument <c>close</c>, and the reply is returned + as value of the current call to the sort or merge function.</p> + + <p>If a function is specified as input and the last input function + returns <c>{end_of_input, Value}</c>, the function specified as output + is called with argument <c>{value, Value}</c>. This makes it easy to initiate the sequence of output functions with a value - calculated by the input functions. - </p> + calculated by the input functions.</p> + <p>As an example, consider sorting the terms on a disk log file. A function that reads chunks from the disk log and returns a list of binaries is used as input. The results are collected in a list of terms.</p> + <pre> sort(Log) -> {ok, _} = disk_log:open([{name,Log}, {mode,read_only}]), @@ -193,29 +220,32 @@ output(L) -> lists:append(lists:reverse(L)); (Terms) -> output([Terms | L]) - end. </pre> - <p>Further examples of functions as input and output can be found - at the end of the <c>file_sorter</c> module; the <c>term</c> - format is implemented with functions. - </p> + end.</pre> + + <p>For more examples of functions as input and output, see + the end of the <c>file_sorter</c> module; the <c>term</c> + format is implemented with functions.</p> + <p>The possible values of <c>Reason</c> returned when an error occurs are:</p> + <list type="bulleted"> <item> - <p><c>bad_object</c>, <c>{bad_object, FileName}</c>. + <p><c>bad_object</c>, <c>{bad_object, FileName}</c> - Applying the format function failed for some binary, or the key(s) could not be extracted from some term.</p> </item> <item> - <p><c>{bad_term, FileName}</c>. <c>io:read/2</c> failed + <p><c>{bad_term, FileName}</c> - <c>io:read/2</c> failed to read some term.</p> </item> <item> - <p><c>{file_error, FileName, file:posix()}</c>. See - <c>file(3)</c> for an explanation of <c>file:posix()</c>.</p> + <p><c>{file_error, FileName, file:posix()}</c> - For an + explanation of <c>file:posix()</c>, see + <seealso marker="kernel:file"><c>file(3)</c></seealso>.</p> </item> <item> - <p><c>{premature_eof, FileName}</c>. End-of-file was + <p><c>{premature_eof, FileName}</c> - End-of-file was encountered inside some binary term.</p> </item> </list> @@ -304,30 +334,53 @@ output(L) -> <funcs> <func> - <name name="sort" arity="1"/> - <fsummary>Sort terms on files.</fsummary> + <name name="check" arity="1"/> + <name name="check" arity="2"/> + <fsummary>Check whether terms on files are sorted.</fsummary> <desc> - <p>Sorts terms on files. <c>sort(FileName)</c> is equivalent - to <c>sort([FileName], FileName)</c>.</p> + <p>Checks files for sortedness. If a file is not sorted, the + first out-of-order element is returned. The first term on a + file has position 1.</p> + <p><c>check(FileName)</c> is equivalent to + <c>check([FileName], [])</c>.</p> </desc> </func> + <func> - <name name="sort" arity="2"/> - <name name="sort" arity="3"/> - <fsummary>Sort terms on files.</fsummary> + <name name="keycheck" arity="2"/> + <name name="keycheck" arity="3"/> + <fsummary>Check whether terms on files are sorted by key.</fsummary> <desc> - <p>Sorts terms on files. <c>sort(Input, Output)</c> is - equivalent to <c>sort(Input, Output, [])</c>.</p> + <p>Checks files for sortedness. If a file is not sorted, the + first out-of-order element is returned. The first term on a + file has position 1.</p> + <p><c>keycheck(KeyPos, FileName)</c> is equivalent + to <c>keycheck(KeyPos, [FileName], [])</c>.</p> </desc> </func> + + <func> + <name name="keymerge" arity="3"/> + <name name="keymerge" arity="4"/> + <fsummary>Merge terms on files by key.</fsummary> + <desc> + <p>Merges tuples on files. Each input file is assumed to be + sorted on key(s).</p> + <p><c>keymerge(KeyPos, FileNames, Output)</c> is equivalent + to <c>keymerge(KeyPos, FileNames, Output, [])</c>.</p> + </desc> + </func> + <func> <name name="keysort" arity="2"/> <fsummary>Sort terms on files by key.</fsummary> <desc> - <p>Sorts tuples on files. <c>keysort(N, FileName)</c> is + <p>Sorts tuples on files.</p> + <p><c>keysort(N, FileName)</c> is equivalent to <c>keysort(N, [FileName], FileName)</c>.</p> </desc> </func> + <func> <name name="keysort" arity="3"/> <name name="keysort" arity="4"/> @@ -335,13 +388,14 @@ output(L) -> <desc> <p>Sorts tuples on files. The sort is performed on the element(s) mentioned in <c><anno>KeyPos</anno></c>. If two - tuples compare equal (<c>==</c>) on one element, next + tuples compare equal (<c>==</c>) on one element, the next element according to <c><anno>KeyPos</anno></c> is compared. The sort is stable.</p> <p><c>keysort(N, Input, Output)</c> is equivalent to <c>keysort(N, Input, Output, [])</c>.</p> </desc> </func> + <func> <name name="merge" arity="2"/> <name name="merge" arity="3"/> @@ -353,39 +407,25 @@ output(L) -> <c>merge(FileNames, Output, [])</c>.</p> </desc> </func> + <func> - <name name="keymerge" arity="3"/> - <name name="keymerge" arity="4"/> - <fsummary>Merge terms on files by key.</fsummary> - <desc> - <p>Merges tuples on files. Each input file is assumed to be - sorted on key(s).</p> - <p><c>keymerge(KeyPos, FileNames, Output)</c> is equivalent - to <c>keymerge(KeyPos, FileNames, Output, [])</c>.</p> - </desc> - </func> - <func> - <name name="check" arity="1"/> - <name name="check" arity="2"/> - <fsummary>Check whether terms on files are sorted.</fsummary> + <name name="sort" arity="1"/> + <fsummary>Sort terms on files.</fsummary> <desc> - <p>Checks files for sortedness. If a file is not sorted, the - first out-of-order element is returned. The first term on a - file has position 1.</p> - <p><c>check(FileName)</c> is equivalent to - <c>check([FileName], [])</c>.</p> + <p>Sorts terms on files.</p> + <p><c>sort(FileName)</c> is equivalent + to <c>sort([FileName], FileName)</c>.</p> </desc> </func> + <func> - <name name="keycheck" arity="2"/> - <name name="keycheck" arity="3"/> - <fsummary>Check whether terms on files are sorted by key.</fsummary> + <name name="sort" arity="2"/> + <name name="sort" arity="3"/> + <fsummary>Sort terms on files.</fsummary> <desc> - <p>Checks files for sortedness. If a file is not sorted, the - first out-of-order element is returned. The first term on a - file has position 1.</p> - <p><c>keycheck(KeyPos, FileName)</c> is equivalent - to <c>keycheck(KeyPos, [FileName], [])</c>.</p> + <p>Sorts terms on files.</p> + <p><c>sort(Input, Output)</c> is + equivalent to <c>sort(Input, Output, [])</c>.</p> </desc> </func> </funcs> |