glob_lock: Lock and access synchronizable z/TPF global field or record

This function reserves exclusive write access to the specified z/TPF global field or record and forces refreshing of the core copy from the most current file copy. You should ensure that a lock is held for the shortest possible time because severe system degradation may result from other ECBs waiting for locks. This function is valid only for synchronizable z/TPF global fields and records.

Last updated

  • Changed in 2021 (information only; no code change).
  • Changed for PUT00.

Format

maketpf_env += system          
#include <tpf/tpfglbl.h>       
#include <tpf/c_globz.h>       
void *glob_lock(unsigned int tagname);
tagname
This argument, which is defined in header file c_globz.h, uniquely identifies the z/TPF global field or record to be locked.

Normal return

This function returns a pointer to the specified z/TPF global field or record's directory entry (for example, a pointer to the field or record's address).

Error return

Not applicable.

Programming considerations

  • The argument coded as tagname must be defined in header file c_globz.h. Results will be unpredictable if this restriction is not heeded.
  • Programs using this function should be prepared to call glob_update, glob_sync or glob_unlock as soon as possible to prevent severe system degradation caused by other ECBs waiting for the lock.
  • After this function call is completed, the tpf_glmod function must be called to ensure that storage protection is set for accessing format-1 globals.
  • Programs using this function should not have any pending I/O operations outstanding because this function may perform the equivalent of a waitc function.
  • This function performs the equivalent of the SYNCC macro. See z/TPF General Services for more information about the SYNCC macro.
  • Use this function only with z/TPF format-1 globals. To lock z/TPF format-2 globals, use the tpf_glOpen function.

Examples

The following example locks and updates a global field that can be synchronized. 
#include <tpf/tpfglbl.h>
#include <tpf/c_globz.h>
⋮
{
    /******************************************************************/
    /* Increment data element mysdata in synchronizable global record */
    /* _mysglob.                                                      */
    /******************************************************************/
    struct mysglbrec **msgrptrptr = glob_lock(_mysglob);
    struct mysglbrec *msgrptr = *msgrptrptr;
    long newdata = msgrptr->mysdata + 1;
    msgrptr->mysdata = newdata;
	 glob_sync(_mysglob);
}