LabJack U3 User Manual
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In the sample code, alternate functions (S or SS versions) can generally be substituted asdesired, changing the parameter types accordingly. All samples here are written in pseudo-CFunctions with an “S” or “SS” appended are provided for programming languages that can’tinclude the LabJackUD.h file and therefore can’t u.se the constants included. It is generally poorrogramming form to hardcode numbers into function calls, if for no other reason than it is hardType parameter with a const char * which is aof the desired constant. Functions with apenLabJackS replaces botheviceType and ConnectionType with strings since both take constants.C, where the LabJackUD.h file can be included and the constants used directly:ddRequest(Handle, LJ_ioGET_CONFIG, LJ_ioHARDWARE_VERSION,0,0,0);ET_CONFIG”, “LJ_ioHARDWARE_VERSION”,0,0,0);s, orh do not take strings. The StringToConstant() functionkes a string and returns the numeric constant. So, for example:LJ_ERROR err;err = AddRequestSS(Handle, “LJ_ioGETCONFIG”, “LJ_ioHARDWARE_VERSION”,0,0,0);if (err == tdo some rOnce agai hif (err == 2)4.1.2 Mu -This driver is c these functions canbe called fBecause of thirequests/resulmultiple threadinto another. I are added, and then results return LJE_NO_DATA_AVAILABLE or aimilar error, chances are the requests and results are in different threads.equest is made in by the thread ID. If a thread is killed andly amhes are created and destroyedontinuously. This will result in the slow consumption of memory as requests on old threads arepto read. Functions with a single “S” replace the IOstring. A string can then be passed with the namedouble “SS” replace both the IOType and Channel with strings. ODFor example:InAThe bad way (hard to read) when LabJackUD.h cannot be included:AddRequest(Handle, 1001, 10, 0, 0, 0);The better way when LabJackUD.h cannot be included, is to pass strings:AddRequestSS(Handle, “LJ_ioGContinuing on this vein, the function StringToConstant() is useful for error handling routinewith the GetFirst/Next functions whictaS ringToConstant(“LJE_INVALID_DEVICE_TYPE”))er or handling..n, t is is much clearer than:lti Threaded Operationompletely thread safe. With some very minor exceptions, allrom multiple threads at the same time and the driver will keep everything straight.s Add, Go, and Get must be called from the same thread for a particular set ofts. Internally the list of requests and results are split by thread. This allowss to be used to make requests without accidentally getting data from one threadf requestssThe driver tracks which thread a rthen a new one is created, it is possible for the new thread to have the same ID. Its not realproblem if Add is called first, but if Get is called on a new thread results could be returned frothe thread that already ended.As mentioned, the list of requests and results is kept on a thread-by-thread basis. Since tdriver cannot tell when a thread has ended, the results are kept in memory for that threadregardless. This is not a problem in general as the driver will clean it all up when unloaded.hen it can be a problem is in situations where threadWc46 |
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