X-Git-Url: http://git.annexia.org/?p=whenjobs.git;a=blobdiff_plain;f=tools%2Fwhenjobs.pod;fp=tools%2Fwhenjobs.pod;h=fe3041baa830650fa48e3e04ce591ad73a0afbab;hp=b8c76a6c6637f2a8c4bc319032ce4bf864234225;hb=2ce29ff559f9bc36733ab2dde5b657eaa76ea8a6;hpb=7ab4d4728286830f96da8d116c61046c1e4cf83a

diff --git a/tools/whenjobs.pod b/tools/whenjobs.pod
index b8c76a6..fe3041b 100644
--- a/tools/whenjobs.pod
+++ b/tools/whenjobs.pod
@@ -592,6 +592,37 @@ this example:
    Whentools.set_variable "name" "Richard";
    Whentools.set_variable_int "counter" 0
 
+=head3 PRE FUNCTIONS
+
+Before a job runs, you can arrange that a C<pre> function is called.
+This function may decide not to run the job (by returning C<false>).
+
+One use for this is to prevent a particular job from running if there
+is already an instance of the same job running:
+
+ job "only one"
+ pre (Whentools.one ())
+ every 10 seconds :
+ <<
+   # Takes longer than 10 seconds to run, but 'Whentools.one ()'
+   # will ensure only one is ever running.
+   sleep 11
+ >>
+
+When using pre functions, jobs must be given an explicit name, ie.
+you must use the C<job> statement.
+
+A number of pre functions are available in the library; see below.
+
+You can also write your own post functions (in OCaml).  The function
+is passed one argument which is a C<Whentools.preinfo> struct, defined
+below.  It should return a boolean: C<true> if the job should run, and
+C<false> if the job should not run.
+
+Note that a fresh serial number (see L</JOBSERIAL>) is assigned to
+each run, whether or not the job actually runs because of
+preconditions.
+
 =head3 POST FUNCTIONS
 
 After a job runs, you can control what happens to its output by
@@ -660,6 +691,22 @@ Here are some examples of using the mailto function:
    # do something
  >>
 
+=item B<Whentools.max> I<n>
+
+This built-in pre function ensures that a maximum of I<n> instances of
+the job are running.
+
+It checks the list of running jobs, and if I<n> or more instances are
+already running, then it returns C<false>, which ensures that the new
+job is not started.
+
+=item B<Whentools.one> I<()>
+
+This built-in pre function ensures that only one instance of the job
+is running.  It is the same as calling:
+
+ Whentools.max 1
+
 =item B<Whentools.set_variable> I<name> I<string>
 
 Set variable I<name> to the string.
@@ -687,6 +734,24 @@ Set variable I<name> to the floating point value I<f>.
 
 =over 4
 
+=item B<Whentools.preinfo>
+
+This structure is passed to pre functions.  It has the following
+fields:
+
+ type preinfo = {
+   pi_job_name : string;           # Job name.
+   pi_serial : Big_int.big_int;    # Job serial number.
+   pi_variables : (string * variable) list; # Variables set in job.
+   pi_running : preinfo_running_job list;   # List of running jobs.
+ }
+ and preinfo_running_job = {
+   pirun_job_name : string;        # Running job name.
+   pirun_serial : Big_int.big_int; # Running job serial number.
+   pirun_start_time : float;       # Running job start time.
+   pirun_pid : int;                # Running job process ID.
+ }
+
 =item B<Whentools.result>
 
 This structure is passed to post functions.  It has the following