<para>To make an executable program, the GHC system compiles your
code and then links it with a non-trivial runtime system (RTS),
- which handles storage management, profiling, etc.</para>
+ which handles storage management, thread scheduling, profiling, and
+ so on.</para>
+
+ <para>
+ The RTS has a lot of options to control its behaviour. For
+ example, you can change the context-switch interval, the default
+ size of the heap, and enable heap profiling. These options can be
+ passed to the runtime system in a variety of different ways; the
+ next section (<xref linkend="setting-rts-options" />) describes
+ the various methods, and the following sections describe the RTS
+ options themselves.
+ </para>
+
+ <sect2 id="setting-rts-options">
+ <title>Setting RTS options</title>
+ <indexterm><primary>RTS options, setting</primary></indexterm>
- <para>You have some control over the behaviour of the RTS, by giving
- special command-line arguments to your program.</para>
+ <para>
+ There are four ways to set RTS options:
+
+ <itemizedlist>
+ <listitem>
+ <para>
+ on the command line between <literal>+RTS ... -RTS</literal>, when running the program
+ (<xref linkend="rts-opts-cmdline" />)
+ </para>
+ </listitem>
+ <listitem>
+ <para>at compile-time, using <option>--with-rtsopts</option>
+ (<xref linkend="rts-opts-compile-time" />)
+ </para>
+ </listitem>
+ <listitem>
+ <para>with the environment variable <envar>GHCRTS</envar>
+ (<xref linkend="rts-options-environment" />)
+ </para>
+ </listitem>
+ <listitem>
+ <para>by overriding “hooks” in the runtime system
+ (<xref linkend="rts-hooks" />)
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
- <para>When your Haskell program starts up, its RTS extracts
- command-line arguments bracketed between
- <option>+RTS</option><indexterm><primary><option>+RTS</option></primary></indexterm>
- and
- <option>-RTS</option><indexterm><primary><option>-RTS</option></primary></indexterm>
- as its own. For example:</para>
+ <sect3 id="rts-opts-cmdline">
+ <title>Setting RTS options on the command line</title>
+
+ <para>
+ If you set the <literal>-rtsopts</literal> flag appropriately
+ when linking (see <xref linkend="options-linker" />), you can
+ give RTS options on the command line when running your
+ program.
+ </para>
+
+ <para>
+ When your Haskell program starts up, the RTS extracts
+ command-line arguments bracketed between
+ <option>+RTS</option><indexterm><primary><option>+RTS</option></primary></indexterm>
+ and
+ <option>-RTS</option><indexterm><primary><option>-RTS</option></primary></indexterm>
+ as its own. For example:
+ </para>
<screen>
-% ./a.out -f +RTS -p -S -RTS -h foo bar
+$ ghc prog.hs -rtsopts
+[1 of 1] Compiling Main ( prog.hs, prog.o )
+Linking prog ...
+$ ./prog -f +RTS -H32m -S -RTS -h foo bar
</screen>
- <para>The RTS will snaffle <option>-p</option> <option>-S</option>
- for itself, and the remaining arguments <literal>-f -h foo bar</literal>
- will be handed to your program if/when it calls
- <function>System.getArgs</function>.</para>
+ <para>
+ The RTS will
+ snaffle <option>-H32m</option> <option>-S</option> for itself,
+ and the remaining arguments <literal>-f -h foo bar</literal>
+ will be available to your program if/when it calls
+ <function>System.Environment.getArgs</function>.
+ </para>
- <para>No <option>-RTS</option> option is required if the
- runtime-system options extend to the end of the command line, as in
- this example:</para>
+ <para>
+ No <option>-RTS</option> option is required if the
+ runtime-system options extend to the end of the command line, as in
+ this example:
+ </para>
<screen>
% hls -ltr /usr/etc +RTS -A5m
</screen>
- <para>If you absolutely positively want all the rest of the options
- in a command line to go to the program (and not the RTS), use a
- <option>––RTS</option><indexterm><primary><option>--RTS</option></primary></indexterm>.</para>
-
- <para>As always, for RTS options that take
- <replaceable>size</replaceable>s: If the last character of
- <replaceable>size</replaceable> is a K or k, multiply by 1000; if an
- M or m, by 1,000,000; if a G or G, by 1,000,000,000. (And any
- wraparound in the counters is <emphasis>your</emphasis>
- fault!)</para>
-
- <para>Giving a <literal>+RTS -f</literal>
- <indexterm><primary><option>-f</option></primary><secondary>RTS option</secondary></indexterm> option
- will print out the RTS options actually available in your program
- (which vary, depending on how you compiled).</para>
-
- <para>NOTE: since GHC is itself compiled by GHC, you can change RTS
- options in the compiler using the normal
- <literal>+RTS ... -RTS</literal>
- combination. eg. to increase the maximum heap
- size for a compilation to 128M, you would add
- <literal>+RTS -M128m -RTS</literal>
- to the command line.</para>
-
- <sect2 id="rts-optinos-environment">
- <title>Setting global RTS options</title>
-
- <indexterm><primary>RTS options</primary><secondary>from the environment</secondary></indexterm>
- <indexterm><primary>environment variable</primary><secondary>for
- setting RTS options</secondary></indexterm>
-
- <para>RTS options are also taken from the environment variable
- <envar>GHCRTS</envar><indexterm><primary><envar>GHCRTS</envar></primary>
- </indexterm>. For example, to set the maximum heap size
- to 128M for all GHC-compiled programs (using an
- <literal>sh</literal>-like shell):</para>
+ <para>
+ If you absolutely positively want all the rest of the options
+ in a command line to go to the program (and not the RTS), use a
+ <option>––RTS</option><indexterm><primary><option>--RTS</option></primary></indexterm>.
+ </para>
+
+ <para>
+ As always, for RTS options that take
+ <replaceable>size</replaceable>s: If the last character of
+ <replaceable>size</replaceable> is a K or k, multiply by 1000; if an
+ M or m, by 1,000,000; if a G or G, by 1,000,000,000. (And any
+ wraparound in the counters is <emphasis>your</emphasis>
+ fault!)
+ </para>
+
+ <para>
+ Giving a <literal>+RTS -?</literal>
+ <indexterm><primary><option>-?</option></primary><secondary>RTS option</secondary></indexterm> option
+ will print out the RTS options actually available in your program
+ (which vary, depending on how you compiled).</para>
+
+ <para>
+ NOTE: since GHC is itself compiled by GHC, you can change RTS
+ options in the compiler using the normal
+ <literal>+RTS ... -RTS</literal>
+ combination. eg. to set the maximum heap
+ size for a compilation to 128M, you would add
+ <literal>+RTS -M128m -RTS</literal>
+ to the command line.
+ </para>
+ </sect3>
+
+ <sect3 id="rts-opts-compile-time">
+ <title>Setting RTS options at compile time</title>
+
+ <para>
+ GHC lets you change the default RTS options for a program at
+ compile time, using the <literal>-with-rtsopts</literal>
+ flag (<xref linkend="options-linker" />). For example, to
+ set <literal>-H128m -K64m</literal>, link
+ with <literal>-with-rtsopts="-H128m -K64m"</literal>.
+ </para>
+ </sect3>
+
+ <sect3 id="rts-options-environment">
+ <title>Setting RTS options with the <envar>GHCRTS</envar>
+ environment variable</title>
+
+ <indexterm><primary>RTS options</primary><secondary>from the environment</secondary></indexterm>
+ <indexterm><primary>environment variable</primary><secondary>for
+ setting RTS options</secondary></indexterm>
+
+ <para>
+ If the <literal>-rtsopts</literal> flag is set to
+ something other than <literal>none</literal> when linking,
+ RTS options are also taken from the environment variable
+ <envar>GHCRTS</envar><indexterm><primary><envar>GHCRTS</envar></primary>
+ </indexterm>. For example, to set the maximum heap size
+ to 2G for all GHC-compiled programs (using an
+ <literal>sh</literal>-like shell):
+ </para>
<screen>
- GHCRTS='-M128m'
+ GHCRTS='-M2G'
export GHCRTS
</screen>
- <para>RTS options taken from the <envar>GHCRTS</envar> environment
- variable can be overridden by options given on the command
- line.</para>
+ <para>
+ RTS options taken from the <envar>GHCRTS</envar> environment
+ variable can be overridden by options given on the command
+ line.
+ </para>
- </sect2>
+ <para>
+ Tip: setting something like <literal>GHCRTS=-M2G</literal>
+ in your environment is a handy way to avoid Haskell programs
+ growing beyond the real memory in your machine, which is
+ easy to do by accident and can cause the machine to slow to
+ a crawl until the OS decides to kill the process (and you
+ hope it kills the right one).
+ </para>
+ </sect3>
+
+ <sect3 id="rts-hooks">
+ <title>“Hooks” to change RTS behaviour</title>
+
+ <indexterm><primary>hooks</primary><secondary>RTS</secondary></indexterm>
+ <indexterm><primary>RTS hooks</primary></indexterm>
+ <indexterm><primary>RTS behaviour, changing</primary></indexterm>
+
+ <para>GHC lets you exercise rudimentary control over the RTS
+ settings for any given program, by compiling in a
+ “hook” that is called by the run-time system. The RTS
+ contains stub definitions for all these hooks, but by writing your
+ own version and linking it on the GHC command line, you can
+ override the defaults.</para>
+
+ <para>Owing to the vagaries of DLL linking, these hooks don't work
+ under Windows when the program is built dynamically.</para>
+
+ <para>The hook <literal>ghc_rts_opts</literal><indexterm><primary><literal>ghc_rts_opts</literal></primary>
+ </indexterm>lets you set RTS
+ options permanently for a given program, in the same way as the
+ newer <option>-with-rtsopts</option> linker option does. A common use for this is
+ to give your program a default heap and/or stack size that is
+ greater than the default. For example, to set <literal>-H128m
+ -K1m</literal>, place the following definition in a C source
+ file:</para>
+
+<programlisting>
+char *ghc_rts_opts = "-H128m -K1m";
+</programlisting>
+
+ <para>Compile the C file, and include the object file on the
+ command line when you link your Haskell program.</para>
+
+ <para>These flags are interpreted first, before any RTS flags from
+ the <literal>GHCRTS</literal> environment variable and any flags
+ on the command line.</para>
+
+ <para>You can also change the messages printed when the runtime
+ system “blows up,” e.g., on stack overflow. The hooks
+ for these are as follows:</para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>
+ <function>void OutOfHeapHook (unsigned long, unsigned long)</function>
+ <indexterm><primary><function>OutOfHeapHook</function></primary></indexterm>
+ </term>
+ <listitem>
+ <para>The heap-overflow message.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <function>void StackOverflowHook (long int)</function>
+ <indexterm><primary><function>StackOverflowHook</function></primary></indexterm>
+ </term>
+ <listitem>
+ <para>The stack-overflow message.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <function>void MallocFailHook (long int)</function>
+ <indexterm><primary><function>MallocFailHook</function></primary></indexterm>
+ </term>
+ <listitem>
+ <para>The message printed if <function>malloc</function>
+ fails.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>For examples of the use of these hooks, see GHC's own
+ versions in the file
+ <filename>ghc/compiler/parser/hschooks.c</filename> in a GHC
+ source tree.</para>
+ </sect3>
+
+ </sect2>
<sect2 id="rts-options-misc">
<title>Miscellaneous RTS options</title>
things like ctrl-C. This option is primarily useful for when
you are using the Haskell code as a DLL, and want to set your
own signal handlers.</para>
+
+ <para>Note that even
+ with <option>--install-signal-handlers=no</option>, the RTS
+ interval timer signal is still enabled. The timer signal
+ is either SIGVTALRM or SIGALRM, depending on the RTS
+ configuration and OS capabilities. To disable the timer
+ signal, use the <literal>-V0</literal> RTS option (see
+ above).
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term>
- <option>-k</option><replaceable>size</replaceable>
+ <option>-ki</option><replaceable>size</replaceable>
<indexterm><primary><option>-k</option></primary><secondary>RTS option</secondary></indexterm>
- <indexterm><primary>stack, minimum size</primary></indexterm>
+ <indexterm><primary>stack, initial size</primary></indexterm>
</term>
<listitem>
- <para>[Default: 1k] Set the initial stack size for
- new threads. Thread stacks (including the main thread's
- stack) live on the heap, and grow as required. The default
- value is good for concurrent applications with lots of small
- threads; if your program doesn't fit this model then
- increasing this option may help performance.</para>
-
- <para>The main thread is normally started with a slightly
- larger heap to cut down on unnecessary stack growth while
- the program is starting up.</para>
- </listitem>
+ <para>
+ [Default: 1k] Set the initial stack size for new
+ threads. (Note: this flag used to be
+ simply <option>-k</option>, but was renamed
+ to <option>-ki</option> in GHC 7.2.1. The old name is
+ still accepted for backwards compatibility, but that may
+ be removed in a future version).
+ </para>
+
+ <para>
+ Thread stacks (including the main thread's stack) live on
+ the heap. As the stack grows, new stack chunks are added
+ as required; if the stack shrinks again, these extra stack
+ chunks are reclaimed by the garbage collector. The
+ default initial stack size is deliberately small, in order
+ to keep the time and space overhead for thread creation to
+ a minimum, and to make it practical to spawn threads for
+ even tiny pieces of work.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <option>-kc</option><replaceable>size</replaceable>
+ <indexterm><primary><option>-kc</option></primary><secondary>RTS
+ option</secondary></indexterm>
+ <indexterm><primary>stack</primary><secondary>chunk size</secondary></indexterm>
+ </term>
+ <listitem>
+ <para>
+ [Default: 32k] Set the size of “stack
+ chunks”. When a thread's current stack overflows, a
+ new stack chunk is created and added to the thread's
+ stack, until the limit set by <option>-K</option> is
+ reached.
+ </para>
+
+ <para>
+ The advantage of smaller stack chunks is that the garbage
+ collector can avoid traversing stack chunks if they are
+ known to be unmodified since the last collection, so
+ reducing the chunk size means that the garbage collector
+ can identify more stack as unmodified, and the GC overhead
+ might be reduced. On the other hand, making stack chunks
+ too small adds some overhead as there will be more
+ overflow/underflow between chunks. The default setting of
+ 32k appears to be a reasonable compromise in most cases.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <option>-kb</option><replaceable>size</replaceable>
+ <indexterm><primary><option>-kc</option></primary><secondary>RTS
+ option</secondary></indexterm>
+ <indexterm><primary>stack</primary><secondary>chunk buffer size</secondary></indexterm>
+ </term>
+ <listitem>
+ <para>
+ [Default: 1k] Sets the stack chunk buffer size.
+ When a stack chunk overflows and a new stack chunk is
+ created, some of the data from the previous stack chunk is
+ moved into the new chunk, to avoid an immediate underflow
+ and repeated overflow/underflow at the boundary. The
+ amount of stack moved is set by the <option>-kb</option>
+ option.
+ </para>
+ <para>
+ Note that to avoid wasting space, this value should
+ typically be less than 10% of the size of a stack
+ chunk (<option>-kc</option>), because in a chain of stack
+ chunks, each chunk will have a gap of unused space of this
+ size.
+ </para>
+ </listitem>
</varlistentry>
<varlistentry>
<listitem>
<para>[Default: 8M] Set the maximum stack size for
an individual thread to <replaceable>size</replaceable>
- bytes. This option is there purely to stop the program
- eating up all the available memory in the machine if it gets
- into an infinite loop.</para>
+ bytes. If the thread attempts to exceed this limit, it will
+ be send the <literal>StackOverflow</literal> exception.
+ </para>
+ <para>
+ This option is there mainly to stop the program eating up
+ all the available memory in the machine if it gets into an
+ infinite loop.
+ </para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
+ <sect2 id="rts-eventlog">
+ <title>Tracing</title>
+
+ <indexterm><primary>tracing</primary></indexterm>
+ <indexterm><primary>events</primary></indexterm>
+ <indexterm><primary>eventlog files</primary></indexterm>
+
+ <para>
+ When the program is linked with the <option>-eventlog</option>
+ option (<xref linkend="options-linker" />), runtime events can
+ be logged in two ways:
+ </para>
+
+ <itemizedlist>
+ <listitem>
+ <para>
+ In binary format to a file for later analysis by a
+ variety of tools. One such tool
+ is <ulink url="http://hackage.haskell.org/package/ThreadScope">ThreadScope</ulink><indexterm><primary>ThreadScope</primary></indexterm>,
+ which interprets the event log to produce a visual parallel
+ execution profile of the program.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ As text to standard output, for debugging purposes.
+ </para>
+ </listitem>
+ </itemizedlist>
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <option>-l<optional><replaceable>flags</replaceable></optional></option>
+ <indexterm><primary><option>-l</option></primary><secondary>RTS option</secondary></indexterm>
+ </term>
+ <listitem>
+ <para>
+ Log events in binary format to the
+ file <filename><replaceable>program</replaceable>.eventlog</filename>,
+ where <replaceable>flags</replaceable> is a sequence of
+ zero or more characters indicating which kinds of events
+ to log. Currently there is only one type
+ supported: <literal>-ls</literal>, for scheduler events.
+ </para>
+
+ <para>
+ The format of the log file is described by the header
+ <filename>EventLogFormat.h</filename> that comes with
+ GHC, and it can be parsed in Haskell using
+ the <ulink url="http://hackage.haskell.org/package/ghc-events">ghc-events</ulink>
+ library. To dump the contents of
+ a <literal>.eventlog</literal> file as text, use the
+ tool <literal>show-ghc-events</literal> that comes with
+ the <ulink url="http://hackage.haskell.org/package/ghc-events">ghc-events</ulink>
+ package.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <option>-v</option><optional><replaceable>flags</replaceable></optional>
+ <indexterm><primary><option>-v</option></primary><secondary>RTS option</secondary></indexterm>
+ </term>
+ <listitem>
+ <para>
+ Log events as text to standard output, instead of to
+ the <literal>.eventlog</literal> file.
+ The <replaceable>flags</replaceable> are the same as
+ for <option>-l</option>, with the additional
+ option <literal>t</literal> which indicates that the
+ each event printed should be preceded by a timestamp value
+ (in the binary <literal>.eventlog</literal> file, all
+ events are automatically associated with a timestamp).
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ The debugging
+ options <option>-D<replaceable>x</replaceable></option> also
+ generate events which are logged using the tracing framework.
+ By default those events are dumped as text to stdout
+ (<option>-D<replaceable>x</replaceable></option>
+ implies <option>-v</option>), but they may instead be stored in
+ the binary eventlog file by using the <option>-l</option>
+ option.
+ </para>
+ </sect2>
+
<sect2 id="rts-options-debugging">
<title>RTS options for hackers, debuggers, and over-interested
souls</title>
<varlistentry>
<term>
- <option>-D</option><replaceable>num</replaceable>
+ <option>-D</option><replaceable>x</replaceable>
<indexterm><primary>-D</primary><secondary>RTS option</secondary></indexterm>
</term>
<listitem>
- <para>An RTS debugging flag; varying quantities of output
- depending on which bits are set in
- <replaceable>num</replaceable>. Only works if the RTS was
- compiled with the <option>DEBUG</option> option.</para>
+ <para>
+ An RTS debugging flag; only availble if the program was
+ linked with the <option>-debug</option> option. Various
+ values of <replaceable>x</replaceable> are provided to
+ enable debug messages and additional runtime sanity checks
+ in different subsystems in the RTS, for
+ example <literal>+RTS -Ds -RTS</literal> enables debug
+ messages from the scheduler.
+ Use <literal>+RTS -?</literal> to find out which
+ debug flags are supported.
+ </para>
+
+ <para>
+ Debug messages will be sent to the binary event log file
+ instead of stdout if the <option>-l</option> option is
+ added. This might be useful for reducing the overhead of
+ debug tracing.
+ </para>
</listitem>
</varlistentry>
</term>
<listitem>
<para>Produce “ticky-ticky” statistics at the
- end of the program run. The <replaceable>file</replaceable>
- business works just like on the <option>-S</option> RTS
- option (above).</para>
-
- <para>“Ticky-ticky” statistics are counts of
- various program actions (updates, enters, etc.) The program
- must have been compiled using
- <option>-ticky</option><indexterm><primary><option>-ticky</option></primary></indexterm>
- (a.k.a. “ticky-ticky profiling”), and, for it to
- be really useful, linked with suitable system libraries.
- Not a trivial undertaking: consult the installation guide on
- how to set things up for easy “ticky-ticky”
- profiling. For more information, see <xref
- linkend="ticky-ticky"/>.</para>
+ end of the program run (only available if the program was
+ linked with <option>-debug</option>).
+ The <replaceable>file</replaceable> business works just like
+ on the <option>-S</option> RTS option, above.</para>
+
+ <para>For more information on ticky-ticky profiling, see
+ <xref linkend="ticky-ticky"/>.</para>
</listitem>
</varlistentry>
</sect2>
- <sect2 id="rts-hooks">
- <title>“Hooks” to change RTS behaviour</title>
-
- <indexterm><primary>hooks</primary><secondary>RTS</secondary></indexterm>
- <indexterm><primary>RTS hooks</primary></indexterm>
- <indexterm><primary>RTS behaviour, changing</primary></indexterm>
-
- <para>GHC lets you exercise rudimentary control over the RTS
- settings for any given program, by compiling in a
- “hook” that is called by the run-time system. The RTS
- contains stub definitions for all these hooks, but by writing your
- own version and linking it on the GHC command line, you can
- override the defaults.</para>
-
- <para>Owing to the vagaries of DLL linking, these hooks don't work
- under Windows when the program is built dynamically.</para>
-
- <para>The hook <literal>ghc_rts_opts</literal><indexterm><primary><literal>ghc_rts_opts</literal></primary>
- </indexterm>lets you set RTS
- options permanently for a given program. A common use for this is
- to give your program a default heap and/or stack size that is
- greater than the default. For example, to set <literal>-H128m
- -K1m</literal>, place the following definition in a C source
- file:</para>
-
-<programlisting>
-char *ghc_rts_opts = "-H128m -K1m";
-</programlisting>
-
- <para>Compile the C file, and include the object file on the
- command line when you link your Haskell program.</para>
-
- <para>These flags are interpreted first, before any RTS flags from
- the <literal>GHCRTS</literal> environment variable and any flags
- on the command line.</para>
-
- <para>You can also change the messages printed when the runtime
- system “blows up,” e.g., on stack overflow. The hooks
- for these are as follows:</para>
-
- <variablelist>
-
- <varlistentry>
- <term>
- <function>void OutOfHeapHook (unsigned long, unsigned long)</function>
- <indexterm><primary><function>OutOfHeapHook</function></primary></indexterm>
- </term>
- <listitem>
- <para>The heap-overflow message.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <function>void StackOverflowHook (long int)</function>
- <indexterm><primary><function>StackOverflowHook</function></primary></indexterm>
- </term>
- <listitem>
- <para>The stack-overflow message.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <function>void MallocFailHook (long int)</function>
- <indexterm><primary><function>MallocFailHook</function></primary></indexterm>
- </term>
- <listitem>
- <para>The message printed if <function>malloc</function>
- fails.</para>
- </listitem>
- </varlistentry>
- </variablelist>
-
- <para>For examples of the use of these hooks, see GHC's own
- versions in the file
- <filename>ghc/compiler/parser/hschooks.c</filename> in a GHC
- source tree.</para>
- </sect2>
-
<sect2>
<title>Getting information about the RTS</title>
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projects / ghc-hetmet.git / blobdiff