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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<config.h>
+include	<error.h>
+include	"mtio.h"
+
+.help mtcache
+.nf _________________________________________________________________________
+MTCACHE -- Cache the magtape position (file and record) between file opens.
+The lock file is used for permanent storage, but is only read and written
+when necessary.  When multiple tape files are accessed by a single task the
+tape position is kept in the cache between successive MTOPEN - CLOSE file
+accesses.
+
+	 mt_getpos (mtname, mt)
+	mt_savepos (mt)
+	   mt_sync (status)
+       mt_clrcache ()
+
+SAVEPOS updates the tape descriptor in the cache; SYNC updates the cache
+on disk in the lock file.  SYNC is automatically called at task termination
+time (including during abnormal termination), but is not normally called
+when a tape file is closed.
+
+ERROR RECOVERY is a bit tricky.  If error recovery takes place the ONERROR
+procedures are called first thing, before FIO cleanup takes place.  That means
+that SYNC will be called while the magtape channel is still open, and before
+SAVEPOS has been called by ZCLSMT (which is called by fio_cleanup which is
+called by the main).  If an error occurs on a magtape channel we want to
+record an undefined file position.  We must see that SAVEPOS is called at
+file open time to mark the cache for updating, causing SYNC to write an
+undefined position lock file when the error occurs.  ZCLSMT, when called
+during error recovery, should set the position to undefined but need not
+sync the cache.
+
+The cache is invalidated at process startup time and at SYNC time in case
+the user loads a new tape or runs a different magtape process while the
+current process is idling between tasks.  In other words, the cache is only
+valid while the task using it is executing.
+.endhelp ___________________________________________________________________
+
+define	SZ_CACHE	MT_MAXTAPES
+
+
+# MT_GETPOS -- Return the device position descriptor of a drive given its
+# unit number.
+
+procedure mt_getpos (mtname, mt)
+
+char	mtname[ARB]		#I device name
+int	mt			#I MTIO descriptor
+
+int	slot
+bool	streq()
+include	"mtcache.com"
+include	"mtio.com"
+
+begin
+	# First look in the cache.
+	for (slot=1;  slot <= SZ_CACHE;  slot=slot+1)
+	    if (streq (MT_LKNAME(mt), c_lkname[1,slot])) {
+		call amovi (c_mtdes[1,slot], MT_DEVPOS(mt), LEN_DEVPOS)
+		call strcpy (c_device[1,slot], MT_DEVICE(mt), SZ_DEVICE)
+		call strcpy (c_lkname[1,slot], MT_LKNAME(mt), SZ_LKNAME)
+		call strcpy (c_iodev[1,slot], MT_IODEV(mt), SZ_IODEV)
+		return
+	    }
+
+	# Get the current position from the lock file, if there is one.
+	call mt_read_lockfile (mtname, mt)
+end
+
+
+# MT_SAVEPOS -- Save the current position in the cache.  The entire descriptor
+# is saved since most of the information therein is needed for SYNC, even
+# though only a portion of the information will be used by GETPOS.
+
+procedure mt_savepos (mt)
+
+int	mt			#I MTIO descriptor
+
+int	prev, slot
+bool	streq(), strne()
+extern	mt_sync()
+include	"mtcache.com"
+include	"mtio.com"
+data	prev /0/
+define	cache_ 91
+
+begin
+	# Post termination handler to sync the cache at task termination time.
+	call onerror (mt_sync)
+
+	# Do not update the cache if the file position is undefined.
+	if (MT_FILNO(mt) <= 0)
+	    return
+
+	# Are we updating an entry already in the cache?
+	for (slot=1;  slot <= SZ_CACHE;  slot=slot+1)
+	    if (streq (MT_LKNAME(mt), c_lkname[1,slot]))
+		goto cache_
+
+	# Add the entry to the cache.  Resync the contents of the old slot
+	# if it is for a different drive and has been modified since it was
+	# last synced.
+
+	slot = prev + 1
+	if (slot > SZ_CACHE)
+	    slot = 1
+	prev = slot
+
+	if (c_modified[slot] == YES && strne(MT_LKNAME(mt),c_lkname[1,slot])) {
+	    call amovi (c_mtdes[1,slot], MT_DEVPOS(0), LEN_DEVPOS)
+	    call strcpy (c_device[1,slot], MT_DEVICE(0), SZ_DEVICE)
+	    call strcpy (c_lkname[1,slot], MT_LKNAME(0), SZ_LKNAME)
+	    call strcpy (c_iodev[1,slot], MT_IODEV(0), SZ_IODEV)
+	    call mt_update_lockfile (0)
+	}
+
+cache_
+	call amovi (MT_DEVPOS(mt), c_mtdes[1,slot], LEN_DEVPOS)
+	call strcpy (MT_DEVICE(mt), c_device[1,slot], SZ_DEVICE)
+	call strcpy (MT_LKNAME(mt), c_lkname[1,slot], SZ_LKNAME)
+	call strcpy (MT_IODEV(mt), c_iodev[1,slot], SZ_IODEV)
+	c_modified[slot] = YES
+end
+
+
+# MT_SYNC -- Update all modified entries in the cache.  Set the position to
+# undefined (file=-1) if we are called during error recovery.  We are called
+# at task termination by the IRAF Main.
+
+procedure mt_sync (status)
+
+int	status			#I task termination status
+
+int	slot
+include	"mtcache.com"
+include	"mtio.com"
+
+begin
+	# Update the .lok files of any active devices.
+	for (slot=1;  slot <= SZ_CACHE;  slot=slot+1) {
+	    if (c_modified[slot] == YES) {
+		# If called during error recovery mark the file position undef.
+		if (status != OK) {
+		    call amovi (c_mtdes[1,slot], MT_DEVPOS(0), LEN_DEVPOS)
+		    MT_FILNO(0) = -1
+		    MT_RECNO(0) = -1
+		    call amovi (MT_DEVPOS(0), c_mtdes[1,slot], LEN_DEVPOS)
+		}
+
+		# Update the lockfile.
+		call amovi (c_mtdes[1,slot], MT_DEVPOS(0), LEN_DEVPOS)
+		call strcpy (c_device[1,slot], MT_DEVICE(0), SZ_DEVICE)
+		call strcpy (c_lkname[1,slot], MT_LKNAME(0), SZ_LKNAME)
+		call strcpy (c_iodev[1,slot], MT_IODEV(0), SZ_IODEV)
+
+		# Ignore errors if we are called during error recovery.
+		iferr (call mt_update_lockfile (0))
+		    if (status == OK)
+			call erract (EA_ERROR)
+
+		c_modified[slot] = NO
+		c_device[1,slot] = EOS
+	    }
+	}
+
+	# Invalidate the cache when a task terminates.
+	call mt_clrcache()
+
+	# If we are called during error recovery, set the file position for
+	# all open tapes to undefined to prevent mt_savepos from being called
+	# by zclsmt when the tape file is closed during error recovery.
+
+	if (status != OK)
+	    do slot = 1, MT_MAXTAPES {
+		MT_FILNO(slot) = -1
+		MT_RECNO(slot) = -1
+	    }
+end
+
+
+# MT_CLRCACHE -- Initialize the cache.
+
+procedure mt_clrcache()
+
+int	slot
+include	"mtcache.com"
+
+begin
+	for (slot=1;  slot <= SZ_CACHE;  slot=slot+1) {
+	    c_modified[slot] = NO
+	    c_device[1,slot] = EOS
+	    c_lkname[1,slot] = EOS
+	    c_iodev[1,slot] = EOS
+	    call aclri (c_mtdes[1,slot], LEN_DEVPOS)
+	}
+end