The ZLINK command adds an executable GT.M routine to the current process if the current process does not contain a copy of a routine. If the current process contains a copy of a routine and the routine is not active, the ZLINK command replaces the current routine process with a "new" version. If necessary, the ZLINK command compiles the routine prior to integrating it with the process.
With VIEW "LINK":"RECURSIVE" specified or by starting the process with the environment variable gtm_link set to "RECURSIVE", the ZLINK command adds an executable routine even when a routine with the same name is active and available in the current stack. When a process links a routine with the same name as an existing routine, future calls use the new routine. Prior versions of that routine referenced by the stack remain tied to the stack until they QUIT, at which point they become inaccessible. This provides a mechanism to patch long-running processes.
![[Important]](images/important.jpg) |
Important |
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An active routine is displayed with $STACK() or ZSHOW "S" of the M virtual stack. By default, an attempt to replace an active routine results in a run-time error . To replace an active routine with a new version, either use VIEW "LINK":"RECURSIVE" or remove the active routine from the stack using ZGOTO or the appropriate number of QUITs and then execute the ZLINK command. |
The format of the ZLINK command is:
ZL[INK][:tvexpr] [expr1[:expr2][,...]]
The optional truth-valued expression immediately following the command is a command postconditional that controls whether or not GT.M executes the command.
The optional first expression specifies the pathname of a routine to ZLINK; if ZLINK has an argument, it not only adds the routine to the image, but also sets $ZSOURCE=expr.
If ZLINK has no argument, or expr="", it uses value of $ZSOURCE as the routine specification filename; at least two (2) spaces must follow a ZLINK command with no argument to separate it from the next command on the line.
The optional second expression specifies a string holding MUMPS command qualifiers delimited by a dash (-); the qualifiers control compile options when the current ZLINK requires a compile; if ZLINK omits the second expression, the command uses the $ZCOMPILE intrinsic special variable to determine the compile qualifiers.
An indirection operator and an expression atom evaluating to a list of one or more ZLINK arguments form a legal argument for a ZLINK.
When the ZLINK command specifies a file, GT.M sets $ZSOURCE to that filename. By default, ZLINK and ZEDIT use $ZSOURCE for a filename when they have a missing or null argument. A subsequent ZLINK without an argument is equivalent to ZLINK $ZSOURCE. For more information on $ZSOURCE, see the appropriate section in Chapter 8: “Intrinsic Special Variables”.
![[Note]](images/note.jpg) |
Note |
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In order to ensure compatibility with GT.M versions that do not permit the percent sign (%) in a file name, use an underscore (_) in place of the percent in the ZLINK file name for routines beginning with a percent sign. |
If the expression includes an explicit directory, ZLINK searches only that directory. Otherwise, if $ZROUTINES is not null, a ZLINK command uses $ZROUTINES to locate files. If $ZROUTINES is null, ZLINK uses the current directory. For more information on $ZROUTINES, see the appropriate section in Chapter 8: “Intrinsic Special Variables”.
If the filename contains an explicit file extension, ZLINK processes the file according to the extension, object (.o) or source (usually .m). If the file name does not specify a file extension, ZLINK attempts to find and match both the object and source for a routine.
The following table illustrates how ZLINK processes the three possibilities of file extension.
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ZLINK Operation Summary | |||
|---|---|---|---|
|
EXTENSION SPECIFIED |
EXTENSION SOUGHT BY ZLINK |
RESULT |
|
|
.o |
.m |
||
|
.o |
found |
N/A |
link only |
|
not found |
N/A |
error |
|
|
.m |
N/A |
found |
compile and link |
| N/A |
not found |
error |
|
| None |
not found |
found |
compile and link |
| found | not found | link only | |
| not found | not found | error | |
|
found .o file newer than .m and version okay |
found .m file older than .o |
link only |
|
|
found .o file older than .m or version mismatch |
found .m file newer than .o |
compile and link |
|
If ZLINK compiles a routine and the -OBJECT= qualifier does not redirect the output, it places the resulting object file in the directory indicated by the search criteria. ZLINK incorporates the new object file into the image, regardless of its directory placement.
If the command does not specify compile qualifiers (with expr2) and $ZCOMPILE is null, GT.M uses the default M command qualifiers, -ignore, -labels=lower, -nolist, and -object. For more information on $ZCOMPILE, refer to the appropriate section in Chapter 8: “Intrinsic Special Variables”. For detailed descriptions of the M command qualifiers, see Chapter 3: “Development Cycle”.
For information on producing object files, but not adding them to the current image, see “ZCOMpile”.
Example:
GTM>ZLINK "test"
If ZLINK finds test.m or test.o, it adds the routine test to the current image. If ZLINK does not find test.o, or finds that test.o is older than test.m, GT.M compiles test.m to produce a new test.o, and adds the contents of the new object file to the image. This example assumes "test" is not on the current M stack - if it is on the stack, GT.M gives an error.
Example:
GTM>zlink "test.m":"-noobject -list"
This compiles the routine "test" and produces a listing but no object file. Because the example produces no object file, it must locate an existing object file (which might be the same as any copy in the current image); if there is noexisting object file, GT.M produces an error. While this example shows the use of compilation qualifiers with ZLINK, a -noobject -list compilation might better be done with ZCOMPILE.
Example:
GTM>zlink "sockexamplemulti2" %GTM-E-LOADRUNNING, Cannot ZLINK an active routine sockexamplemulti2 GTM>zshow "S" sockexamplemulti2+12^sockexamplemulti2 (Direct mode) GTM>view "LINK":"RECURSIVE" GTM>zlink "sockexamplemulti2" GTM>
This example demonstrates how VIEW "LINK":"RECURSIVE" command ZLINKs a routine when its prior version is already there in the active M virtual stack.
If a GT.M routine refers to a routine that is not linked in the process memory, GT.M automatically attempts to ZLINK that routine. An auto-ZLINK is functionally equivalent to an explicit ZLINK of a routine without a specified directory or file extension.
The following GT.M commands and functions can initiate auto-ZLINKing:
DO
GOTO
ZBREAK
ZGOTO
ZPRINT
$TEXT()
GT.M auto-ZLINKs the routine if the following conditions are met:
ZLINK can locate and process the routine file, as indicated in the previous ZLINK Operation Summary table
The name of the routine is the same as the name of the source file; the only exception is that GT.M converts a leading percent sign (%) in a file name to an underscore (_).
In GT.M, the name of the source file determines the name of the GT.M routine. The file name of the object file is not required to match the name of the routine. Linking the object file makes the internal routine name (derived from the source file) known to GT.M. This can lead to potential confusion, however, since both ZLINK and auto-ZLINK use the name of the object file to find the routine. When the object file name differs from the name of the routine, auto-ZLINK generates a run-time error.
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Note |
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Auto-ZLINK and ZLINK commands without a .m or .o file extension in their argument determine the need to recompile based on whether the object file was more recently modified than the source file using time in nanoseconds, as provided by the underlying system call. Note that, although the format of the file modification timestamps provides a nanosecond granularity, many supported OSs currently update the file timestamps with an accuracy of one second. |