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smlist

shared memory list management library

    #include "smlist.h"
    typedef int (*SmListCompareFn)
        (PsmPartition partition, PsmAddress eltData, void *argData);
    typedef void (*SmListDeleteFn)
        (PsmPartition partition, PsmAddress elt, void *argument);
    [see description for available functions]

The smlist library provides functions to create, manipulate and destroy doubly-linked lists in shared memory. As with lyst(3), smlist uses two types of objects, list objects and element objects. However, as these objects are stored in shared memory which is managed by psm(3), pointers to these objects are carried as PsmAddress values. A list knows how many elements it contains and what its first and last elements are. An element knows what list it belongs to and the elements before and after it in its list. An element also knows its content, which is normally the PsmAddress of some object in shared memory.

Create a new list object without any elements in it, within the memory segment identified by partition. Returns the PsmAddress of the list, or 0 on any error.
Unwedge, as necessary, the mutex semaphore protecting shared access to the indicated list. For details, see the explanation of the sm_SemUnwedge() function in platform(3).
Empty a list. Frees each element of the list. If the delete function is non-NULL, that function is called once for each freed element; when called, that function is passed the PsmAddress of the list element and the argument pointer passed to sm_list_clear(). Returns 0 on success, -1 on any error.
Destroy a list. Same as sm_list_clear(), but additionally frees the list structure itself. Returns 0 on success, -1 on any error.
Set the value of a user data variable associated with the list as a whole. This value may be used for any purpose; it is typically used to store the PsmAddress of a shared memory block containing data (e.g., state data) which the user wishes to associate with the list. Returns 0 on success, -1 on any error.
Return the value of the user data variable associated with the list as a whole, or 0 on any error.
Return the number of elements in the list.
Create a new list element whose data value is data and insert it into the given list. If the compare function is NULL, the new list element is simply appended to the list; otherwise, the new list element is inserted after the last element in the list whose data value is "less than or equal to" the data value of the new element (in dataBuffer) according to the collating sequence established by compare. Returns the PsmAddress of the new element, or 0 on any error.
Create a new list element and insert it at the start/end of a list. Returns the PsmAddress of the new element on success, or 0 on any error. Disregards any established sort order in the list.
Create a new list element and insert it before/after a given element. Returns the PsmAddress of the new element on success, or 0 on any error. Disregards any established sort order in the list.
Delete an element from a list. If the delete function is non-NULL, that function is called upon deletion of elt; when called, that function is passed the PsmAddress of the list element and the argument pointer passed to sm_list_delete(). Returns 0 on success, -1 on any error.
Return the PsmAddress of the first/last element in list, or 0 on any error.
Return the PsmAddress of the element following/preceding elt in that element's list, or 0 on any error.
Search a list for an element whose data matches the data in dataBuffer. If the compare function is non-NULL, the list is assumed to be sorted in the order implied by that function and the function is automatically called once for each element of the list until it returns a value that is greater than or equal to zero (where zero indicates an exact match and a value greater than zero indicates that the list contains no matching element); each time compare is called it is passed the PsmAddress that is the element's data value and the dataBuffer value passed to sm_list_search(). If compare is NULL, then the entire list is searched until an element is located whose data value is equal to ((PsmAddress) dataBuffer). Returns the PsmAddress of the matching element if one is found, 0 otherwise.
Return the PsmAddress of the list to which elt belongs, or 0 on any error.
Return the PsmAddress that is the data value for elt, or 0 on any error.
Set the data value for elt to data, replacing the original value. Returns the original data value for elt, or 0 on any error. The original data value for elt may or may not have been the address of an object in memory; even if it was, that object was NOT deleted.

Warning: changing the data value of an element of an ordered list may ruin the ordering of the list.

A user normally creates an element and adds it to a list by doing the following:

1
obtaining a shared memory block to contain the element's data;
2
converting the shared memory block's PsmAddress to a character pointer;
3
using that pointer to write the data into the shared memory block;
4
calling one of the sm_list_insert functions to create the element structure (which will include the shared memory block's PsmAddress) and insert it into the list.

When inserting elements or searching a list, the user may optionally provide a compare function of the form:

    int user_comp_name(PsmPartition partition, PsmAddress eltData, 
                       void *dataBuffer);

When provided, this function is automatically called by the smlist function being invoked; when the function is called it is passed the content of a list element (eltData, nominally the PsmAddress of an item in shared memory) and an argument, dataBuffer, which is nominally the address in local memory of some other item in the same format. The user-supplied function normally compares some key values of the two data items and returns 0 if they are equal, an integer less than 0 if eltData's key value is less than that of dataBuffer, and an integer greater than 0 if eltData's key value is greater than that of dataBuffer. These return values will produce a list in ascending order. If the user desires the list to be in descending order, the function must reverse the signs of these return values.

When deleting an element or destroying a list, the user may optionally provide a delete function of the form:

    void user_delete_name(PsmPartition partition, PsmAddress elt, void *argData)

When provided, this function is automatically called by the smlist function being invoked; when the function is called it is passed the address of a list element (elt and an argument, argData, which if non-NULL is normally the address in local memory of a data item providing context for the list element deletion. The user-supplied function performs any application-specific cleanup associated with deleting the element, such as freeing the element's content data item and/or other memory associated with the element.

For an example of the use of smlist, see the file smlistsh.c in the utils directory of ICI.

lyst(3), platform(3), psm(3)