Abstract:
A dynamically loadable file, such as a dynamically loadable device driver or library, is delayed from being unloaded from memory for improved memory management and processing operations including reduced unload/load cycles. Prior to terminating execution of select functions, a dynamically loadable driver spawns a delay process that loads the driver and keeps it loaded for a period of time beyond that which it would normally be loaded. Thus, even after a calling process unloads the driver, it remains loaded for a period of time longer because of the spawned delay process and allows the operating system or an application/process to use the driver again within the delay time without requiring the driver to be re-copied into memory or re-initialized. The delay process safely increments the operating system reference count for the driver to keep the driver loaded and then monitors a delay time to subsequently unload the driver.

Description:
This is a continuation of application Ser. No. 09/288,942 filed on Apr. 4, 1999 now U.S. Pat. No. 6,308,184, which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to computer peripheral device drivers and, more particularly, to dynamically loadable printer drivers. 
     BACKGROUND OF THE INVENTION 
     A device driver is software that controls a hardware component or peripheral device of a computer, such as a printer. A device driver is responsible for accessing the hardware registers of the device and often includes an interrupt handler to service interrupts generated by the device or an application executing on the computer. Conventionally, a device driver was linked to the operating system (O.S.) kernel when the kernel was built. However, recent operating systems have dynamically loadable/linkable device drivers that are installed from files after the operating system is running. For example, in the Windows® 95/98 operating systems provided by Microsoft Corp., dynamically loadable/linkable drivers (files or code) are identified with a .DRV extension in the file name, and dynamically loadable libraries are identified with a .DLL extension. More recently, dynamically loadable code in general, whether it be a “driver” or a “library”, is identified simply with a .DLL extension. Such operating systems, drivers, and/or libraries provide flexibility for overall memory management operations and computing performance efficiency considerations. For purposes of this discussion, a dynamically loadable/linkable driver, library and/or other code having data and/or executable instructions will simply be referred to herein as a DLL file. Additionally, the terms “load” and “link” will be referred to jointly herein simply as “load”. Moreover, the discussion will occur in the context of a printer driver, although other drivers and/or dynamically loadable/linkable files are equally applicable. 
     Typically, the operating system “loads” a DLL file when an application or other executing process requests to use it. An application is a self-contained program that performs a specific function or duty, typically for the user. Examples include a word processor, graphic design package, electronic mail program, etc. Generally, the O.S. loads the DLL file by: (i) copying the DLL file from an external storage medium, such as a disk drive, into random access memory (RAM) for execution if it is not already resident in RAM, (ii) setting and/or incrementing an internal reference count for that DLL file, (iii) initializing the DLL file, and (iv) linking the application/process with the DLL file (or in other words, establishing communication between the application and the DLL file) so that the application can execute any one of a collection of functions residing in the DLL file. The internal reference count allows the O.S. to track how many applications or processes are currently using the DLL file. This enables the O.S. to determine whether or not the DLL file is already resident in memory and to bring it into memory (RAM) only if it is not already resident. For example, if the DLL file is not already resident in memory (i.e., the reference count is zero), then a “load” of the DLL file includes placing it in memory (i.e., copied from disk) for execution and setting/incrementing the reference count. On the other hand, if the DLL file is already resident in memory when an application needs to use it (i.e., the reference count is a non-zero value), then a “load” simply includes incrementing the reference count to reflect another use of the DLL file. 
     Additionally, the reference count enables the O.S. to determine when to unload the DLL file. Generally, the O.S. unloads the DLL file by (i) decrementing the internal reference count for that DLL file, (ii) de-initializing the DLL file, and (iii) unlinking the application/process from the DLL file (or in other words, breaking communication between the application and the DLL file) and removing the DLL file out of RAM (i.e., marking its memory space as unused). For example, if no other application is currently using the DLL file (i.e., if the reference count will go to zero) when an application completes its use of the DLL file, then an “unload” includes decrementing the reference count and removing the DLL file from memory (marking its memory space as “unused”). If another application/process is currently using the DLL file (i.e., the reference count will not go to zero), then an “unload” simply includes decrementing the reference count, and the DLL file is kept resident in memory for continued use by the other application(s). 
     The loading and unloading of a DLL file can occur multiple times over a very short period of time. For example, when an application is initially launched (executed), a printer driver DLL file is loaded and unloaded multiple times by the O.S. for the application to initially establish communication with the printer device. An application initiates communication with a DLL file by creating (requesting via the O.S.) a device context for that device DLL file. This is commonly referred to as a “CreateDC( )” command in a Windows 95/98 environment and is the mechanism that enables the O.S. to establish the communication structure and parameters between the application and the driver DLL file. To this regard, in a printer driver context, a CreateDC( ) or similar command typically executes a series of “query” functions including, for example, the O.S. loading the printer driver to determine what the driver version number is (i.e., executing a driver version detect function in the DLL file), and then unloading the driver; loading the printer driver to inquire what the resolution capability of the printer is (i.e., executing a resolution detect function in the DLL file), and then unloading the driver; loading the printer driver to inquire what paper size the printer supports (i.e., executing a paper size detect function in the DLL file), and then unloading the driver; loading the printer driver to inquire what the paper orientation is (i.e., executing an orientation detect function in the DLL file), and then unloading the driver; and so forth for other printer features also. Finally, after this series of loading/unloading occurs to query the printer driver, an “enabling” function is executed in the DLL file to enable or create the device context for the driver for further use by the application. 
     As indicated, the sequence of the above noted load/unload functions may be performed by the O.S. for each CreateDC( ) command executed by the application. Other functions provided by the DLL file may also be called by the application once the device context is established. In any case, after the application has completed its calls to the DLL file subsequent to a CreateDC( ) command, the application executes a DeleteDC( ) command to break the communication link between the application and the DLL file. In other words, the O.S. “unloads” the driver. Note also that an application may execute CreateDC( ) and DeleteDC( ) commands multiple times in its program code, depending on design criteria, desired execution efficiency, memory considerations, and other factors. 
     Although one idea behind unloading a DLL file is to free up memory resources, a potential effect of multiple instances of loading and unloading a DLL file in a short period of time is to undesirably tax a system&#39;s processor and memory resources because of the intensive file and memory management activities that occur. Additionally, the initialization and de-initialization of the DLL file each time it is loaded into memory and subsequently unloaded causes a lot of code to be processed repeatedly which can be perceived as a performance problem. Notably, this performance penalty becomes more severe the larger the DLL file becomes and the more complex the initialization and de-initialization code becomes (as drivers become more and more sophisticated). Disadvantageously, these events can result in undesirable processing delays that may even be noticed by a user. 
     Accordingly, an object of the present invention is to provide a tool and method for managing dynamically loadable/linkable files. 
     SUMMARY OF THE INVENTION 
     According to principles of the present invention in a preferred embodiment, a dynamically loadable file, such as a DLL device driver or library, is delayed from being unloaded from memory for improved memory management and processing operations including reduced unload/load cycles. Prior to terminating execution of a given library function, a DLL driver spawns a delay process that loads the driver and keeps it loaded for a period of time beyond that which it would normally be loaded relative to its calling process. Thus, even after a calling process unloads the driver, it remains loaded for a period of time longer because of the spawned delay process, thereby allowing the operating system or an application/process to use the driver again within the delay time without requiring the driver to be re-copied into memory or re-initialized. The delay process safely increments the operating system reference count for the driver to keep the driver loaded and then monitors a delay time event to subsequently unload the driver. 
     Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a host computer and peripheral printer device, wherein a dynamically loadable printer driver and delay process are employed according to one embodiment of the present invention. 
     FIG. 2 is a flow chart depicting a preferred method of the present invention for delaying the unloading of a DLL file. 
     FIG. 3 is a flow chart depicting one embodiment of a method for enabling a DLL file. 
     FIG. 4 is a flow chart depicting one embodiment of a method for loading a DLL file. 
     FIG. 5 is a flow chart depicting one embodiment of a method for disabling a DLL file. 
     FIG. 6 is a flow chart depicting one embodiment of a method for unloading a DLL file. 
     FIG. 7 is a flow chart depicting a preferred method for a delay process for delaying the unloading a DLL filed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of a host computer  10  and peripheral printer device  15 , wherein a dynamically loadable printer driver  20  and delay process  25  are employed according to one embodiment of the present invention. Host computer  10  is any conventional computing device, such as a personal computer, having a processor  30 , a disk drive  35 , and random access memory (RAM)  40 , all communicating via bus  45 . Host computer  10  is enabled to execute a conventional operating system  50  that is capable of executing at least one application  55 , and that is capable of loading and unloading a dynamically loadable driver or library  20 , commonly referred to as a .DRV or .DLL file respectively (again, referred to herein jointly as a DLL file for ease of discussion purposes). Disk drive  35  may be a local drive or a remote (networked) drive. For purposes of discussion, peripheral device  15  is a printer, such as a conventional laser printer, and is coupled to host computer  10  via conventional cabling or other wireless technology  60 . It should be noted, however, that the present invention is similarly applicable to other peripheral devices, including other imaging devices such as a copier, facsimile machine, scanner, or the like. purposes). Disk drive  35  may be a local drive or a remote (networked) drive. For purposes of discussion, peripheral device  15  is a printer, such as a conventional laser printer, and is coupled to host computer  10  via conventional cabling or other wireless technology  60 . It should be noted, however, that the present invention is similarly applicable to other peripheral devices, including other imaging devices such as a copier, facsimile machine, scanner, or the like. 
     Dynamically loadable driver  20  enables computer  10  to print to printer  15  and includes executable code (instructions) for providing user interface capabilities for displaying on display  65  and other conventional functions for communicating with printer  15 . Exemplary functions include, but are not limited to, a driver version detect function, a resolution detect function, a paper size detect function, and a paper orientation detect function. 
     Importantly, under principles of the present invention in a preferred embodiment, driver  20  includes executable instructions for spawning a delay process  25 . Delay process  25  is a special application provided with driver  20  for printer  15  in this example. However, delay process  25  is also similarly applicable to other printers and/or peripherals. Preferably, delay process  25  is spawned near the end of execution of one or more selected functions in driver  20  where it is not unreasonable to expect that there will be another call into the driver. As a spawned process (i.e., a “child” process of driver  20  in a multitasking operating system), delay process  25  executes independently of driver  20  and provides a tool for “delaying” the unloading of driver  20  by loading driver  20  and safely incrementing the O.S. internal reference count for the driver. Delay process  25  is not visible or noticed by a user. However, it delays the unloading of driver  20  long enough to give O.S.  50  or the printing application  55  sufficient chance to load driver  20  again (if needed) while driver  20  is still loaded in memory  40  by delay process  25 . By keeping driver  20  loaded for an extended period, the performance overhead of O.S.  50  for reloading driver  20  is mitigated. In other words, unload/load cycles are reduced. 
     Referring now to FIGS. 2-7, these flow charts depict a preferred method of the present invention and are best understood in context of also referring to FIG.  1 . To this regard, FIG. 2 is an overview process of the invention for loading and unloading a dynamically loadable file wherein the DLL file is delayingly unloaded. First,  105 , an application/process  55  loads a DLL driver  20 . This is accomplished, for example, by executing a “create-device-context” (CreateDC( )) command (or similar command) to have O.S.  50  load driver  20 . Subsequently, O.S.  50  or application  55  executes a function call  110  to driver  20 . For example, in the case of O.S.  50  initially enabling and loading driver  20  in response to a CreateDC( ) command, a query function call is executed such as for detecting the driver version number or for detecting the resolution of printer  15 , etc. Importantly, after the function is executed  110 , driver  20  spawns  115  delay process  25 . Once spawned, delay process  25  executes independently of application  55  and executes a load command  120  to load driver  20  whereby the internal reference count is incremented in O.S.  50  for the driver. 
     It should be noted here that in a preferred embodiment, delay process  25  is spawned only after a certain function or functions execute in driver  20  where it is not unreasonable to expect that there will be another call into the driver. For example, delay process  25  is spawned after any query function and after a disable driver function. 
     When application/process  55  completes its use of driver  20 , the driver is unloaded  125 . This is accomplished, for example, by the application executing a “delete-device-context” (DeleteDC( )) command (or similar command) to have O.S.  50  unload driver  20  and decrement the reference count. However, delay process  25  keeps driver  20  loaded for a while even after application  55  unloads it since delay process  25  previously loaded the driver  120  which caused O.S.  50  to increment the reference count. Only after a given event, such as a timer event, does delay process  25  unload  130  driver  20  by further decrementing the reference count and/or removing the driver from memory  40 . Importantly, keeping driver  20  loaded for this extra time period can significantly reduce overhead processing and memory manipulation requirements of O.S.  50 . For example, driver  20  will not need to be copied in from disk  35  again if another driver load is initiated (i.e., by application  55 , some other process, or O.S.  50 ) while the driver is still loaded by delay process  25 . Additionally, the initialization and de-initialization code of driver  20  will not need to be re-executed since delay process  25  keeps driver  20  loaded. 
     FIG. 3 is a flow chart depicting a method of the present invention as embodied in association with an exemplary process of creating a device context (for example, CreateDC( )) for enabling a DLL file (driver  20 ) as initiated by application  55 . First,  165 , driver  20  is loaded into memory  40  by O.S.  50  (if it is not already resident there) and its reference count is set and incremented (see FIG.  4 ). Next,  170 , driver  20  is linked to application  55  so that the application can execute the functions provided by driver  20 . Subsequently, O.S.  50  executes one or more query functions  175  in driver  20  to establish a proper context with driver  20 . Again, for driver  20  relative to printer  15 , query functions may include, for example, detecting driver version, printer resolution, media size, media orientation, etc. Importantly, upon completion of or near the end of a query function  175 , the present invention delay process  25  is spawned  180  by driver  20  to load driver  20 . Only after delay process  25  is spawned  180  does O.S.  50  then unload  185  driver  20 . However, advantageously, delay process  25  actually keeps driver  20  loaded in memory  40  for a while longer beyond the unload  185 . 
     If more device queries are to occur  190 , then O.S.  50  again loads (reloads)  165  driver  20 . But, this time, driver  20  doesn&#39;t need to be copied in from disk  35  because delay process  25  has kept it loaded if the new load  165  occurs within the delay time set in delay process  25 . Consequently, only the reference count for driver  20  is incremented (see FIG.  4 ). After the driver is linked  170  and another query function is executed  175 , driver  20  again spawns  180  delay process  25 . If delay process  25  is still executing from its previous spawn by driver  20 , then the delay time for unloading driver  20  is simply reset. Otherwise, delay process  25  is spawned anew (see FIG.  7 ). 
     As can be seen, a series of query calls to driver  20  typically causes multiple loads and unloads of driver  20  as depicted by the looping flow in FIG.  3 . However, the present invention delay process  25  in association with a DLL file  20  reduces the number of DLL unload/load cycles for improved performance and efficiency. 
     Finally, when all of the query functions have been executed  190  as dictated by O.S.  50 , then the enable function  195  is executed in driver  20  by O.S.  50  to finish creating the device context by initializing the driver and associated hardware for enabling application  55  to use the library of functions provided by driver  20 . 
     FIG. 4 is a flow chart of a method for loading a DLL file (driver  20 ) for use. First, if driver  20  is already resident  205  in memory  40 , then O.S.  50  simply increments  210  an internal reference count for that driver  20 . No other significant memory manipulations or re-initialization of driver code needs to occur. On the other hand, if driver  20  is not already resident  205  in memory  40 , then O.S.  50  copies  215  the driver from disk  35  into memory  40 . Additionally, O.S.  50  sets the reference count  220  for driver  20  equal to zero and initializes the driver  225  (i.e., executes the driver&#39;s initialization code). Subsequently, the internal reference count is incremented  210  to reflect the load. 
     It should be noted here that when delay process  25  loads driver  20  (see FIG. 2,  120 ; FIG. 3,  180 ; and FIG. 7,  355 ), it is loaded simply by O.S.  50  incrementing the internal reference count  210 . This is sufficient because driver  20  is always already loaded in memory  205  anytime delay process  25  is spawned by driver  20 . 
     FIG. 5 is a flow chart depicting a method of the present invention as embodied in association with an exemplary process of deleting a device context (for example, DeleteDC( )) for disabling a DLL file (driver  20 ) as initiated by application  55 . First, a disable function  255  is executed in driver  20  for clearing the device context previously established. Next, upon completion of or near the end of disable function  255 , the present invention delay process  25  is spawned  257  by driver  20  to load driver  20 . Only after delay process  25  is spawned  257  does O.S.  50  then unload  260  driver  20  due to completion of the disable function  255 . However, advantageously, delay process  25  actually keeps driver  20  loaded in memory  40  for a while longer beyond the unload  260 . Importantly, this reduces unload/load cycles for driver  20  in the event driver  20  is again loaded (either by O.S.  50 , application  55 , or some other process) within the delay time set in delay process  25 . 
     FIG. 6 is a flow chart depicting a method for unloading a DLL file (driver  20 ) after use. First,  305 , the internal reference count for driver  20  is decremented. Then, if the reference count equals zero  310 , O.S.  50  de-initializes  315  driver  20  (i.e., executes de-initialization code) and removes it  320  from memory  40 . As conventional in:the art, removal may be as simple as marking the memory space used by driver  20  as “unused”. 
     If the reference count does not equal zero  310 , O.S.  50  does nothing. In other words, the reference count indicates some application or process is still using driver  20  and, as such, it should not be removed from memory  40  at this time. For example, if application  55  initiated the unload after using driver  20 , delay process  25  may still have the driver loaded under the present invention. 
     Referring now to FIG. 7, this flow chart depicts a preferred method of the present invention delay process  25 . When driver  20  spawns delay process  25 , it passes certain command line parameters, including (i) an identifier that identifies the parent process (driver  20 ), and (ii) a time parameter that identifies how long delay process  25  is to keep driver  20  loaded. In general, these parameters enable delay process  25  to work for any DLL file without having to make a special delay process for each DLL file. In any case, once it is spawned, delay process  25  loads  355  driver  20 . Since driver  20  is already loaded, the internal reference count in O.S.  50  is simply incremented (FIG. 4, steps  205 ,  210 ). 
     Subsequently, an event timer is set  360  using the time parameter passed in. In a preferred embodiment, the timer is simply a counter that decrements a time-to-live timer count value (initially the time parameter passed in) at each passage of a given interval of time. Preferably, the interval is derived in accordance with a system clock obtained from O.S.  50  and/or computer  10 . For example, a preferred interval is every one second in time. However, other delay intervals are similarly applicable and may be tuned based on the speed of processor  30  and/or host  10 . 
     Next, delay process  25  simply waits  365  until a timer message/event is received from O.S.  50  indicating the interval has lapsed. Although a “busy wait” loop is implied  365  in FIG. 7, an actual implementation in a Windows environment is event driven, i.e., the application releases control to the O.S. until an event is received. If a timer message is received  365  (for example, one second passes), then the time-to-live timer count is decremented  370 . If the timer count is not zero  375 , then delay process  25  simply waits for another timer message  365 . This process of waiting for a timer message  365 , and decrementing the timer count  370  continues until the time-to-live timer count equals zero. Once the event occurs such that the timer count equals zero,  375 , delay process  25  unloads  380  driver  20  (see FIG. 6) and terminates. 
     Importantly, the internal reference count for driver  20  is safely increased in O.S.  50  when driver  20  is loaded by delay process  25 . It is safely increased because driver  20  doesn&#39;t have to do anything to be sure that the reference count eventually goes to zero when it should. The reference count eventually goes to zero when the time-to-live timer count in delay process  25  is finally decremented to zero, thus ensuring that driver  20  will ultimately be unloaded. This occurs simply in a matter of time and relatively independent of what else is happening in computer  10 . 
     It should also be noted that in a preferred embodiment, if delay process  25  already has driver  20  loaded when its command line is parsed, then driver  20  is not loaded again but, rather, delay process  25  simply resets its timer count to the new command line time parameter passed in. 
     In summary, the present invention provides a system and method for delaying the unloading of a dynamically loadable driver or library. Advantageously, driver performance and memory management is improved, and unload/load cycles are reduced. It will be obvious to one of ordinary skill in the art that the present invention is easily implemented utilizing any of a variety of components and tools existing in the art. Moreover, while the present invention has been described by reference to specific embodiments, it will be apparent that other alternative embodiments and methods of implementation or modification may be employed without departing from the true spirit and scope of the invention.