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<HTML><HEAD>
<TITLE>C Examples -- Example 6: tclcs</TITLE>
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<a name="16870">
</a><h3>Example 6: tclcs</h3>
<p><a name="16889">
</a>The following example adds critical section <code>enter</code> and <code>leave</code> commands to Tcl. This allows you to protect shared resources (i.e., an external file or remote connection) accessed in a Tcl script.</p>
<p><a name="16887">
</a>This example can be found in the <code>examples/c/tclcs</code> directory.</p>
<pre> <a name="16866"></a>
<a name="16901"></a>#include "ns.h"
<a name="16906"></a>#include "nstcl.h"
<a name="16907"></a>
<a name="16908"></a>/*
<a name="16909"></a> * This code implements simple critical section primitives as TCL commands
<a name="16910"></a> * within the AOLserver. To use this module, add the following to the
<a name="16911"></a> * [ns\server\server-name\modules] section of your nsd.ini file:
<a name="16912"></a> * cs=tclcs.dll ; or tclcs.so on Unix platforms
<a name="16913"></a> *
<a name="16914"></a> * Within your TCL, these commands should be used as follows:
<a name="16915"></a> * ...
<a name="16916"></a> * cs_enter
<a name="16917"></a> * set err [catch {some tcl}]
<a name="16918"></a> * cs_leave
<a name="16919"></a> * if $err {
<a name="16920"></a> * error $err
<a name="16921"></a> * }
<a name="16922"></a> * ...
<a name="16924"></a> * Note that any error should be caught to avoid leaving the
<a name="16925"></a> * critical section in the locked state after the script exits.
<a name="16926"></a> *
<a name="16927"></a> * Also, because the init function uses the module name to construct
<a name="16928"></a> * the command names, you can load the module multiple times if you
<a name="16929"></a> * need more than one critical section. For example, if you needed 2
<a name="16930"></a> * critical sections, your nsd.ini would have:
<a name="16931"></a> *
<a name="16932"></a> * [ns\server\server-name\modules]
<a name="16933"></a> * cs1=tclcs.dll
<a name="16934"></a> * cs2=tclcs.dll
<a name="16935"></a> *
<a name="16936"></a> * and then, in your Tcl script, you would access the two critical
<a name="16937"></a> * sections using their unique names:
<a name="16938"></a> *
<a name="16939"></a> * ...
<a name="16940"></a> * cs1_enter
<a name="16941"></a> * ... access resource protected by cs 1 ...
<a name="16942"></a> * cs2_enter
<a name="16943"></a> * ... access resource 2, leaving resource 1 locked ...
<a name="16944"></a> * cs2_leave
<a name="16945"></a> * cs1_leave
<a name="16946"></a> *
<a name="16947"></a> */
<a name="16948"></a>
<a name="16949"></a>int Ns_ModuleVersion = 1;
<a name="16950"></a>
<a name="16951"></a>static int InitCs(Tcl_Interp *interp, void *ctx);
<a name="16952"></a>static Tcl_CmdProc EnterCs, LeaveCs;
<a name="16953"></a>
<a name="16954"></a>/*
<a name="16955"></a> * This structure is used to pass the critical section
<a name="16956"></a> * and enter and leave command names to InitCs function
<a name="16957"></a> * through the Ns_TclInitInterps function.
<a name="16958"></a> */
<a name="16959"></a>typedef struct {
<a name="16960"></a> char *enter;
<a name="16961"></a> char *leave;
<a name="16962"></a> Ns_CriticalSection *cs;
<a name="16963"></a>} CsCtx;
<a name="16964"></a>
<a name="16965"></a>
<a name="16966"></a>/*
<a name="16967"></a> * Ns_ModuleInit - The function is called each time the
<a name="16968"></a> * tclcs module is loaded into a server. It
<a name="16969"></a> * constructs the names of the enter and leave Tcl commands
<a name="16970"></a> * from the module name and then calls Ns_TclInitInterps
<a name="16971"></a> * to add the command to each interpreter of the
<a name="16972"></a> * server.
<a name="16973"></a> */
<a name="16974"></a>int
<a name="16975"></a>Ns_ModuleInit(char *hServer, char *hModule)
<a name="16976"></a>{
<a name="16977"></a> Ns_DString dsEnter;
<a name="16978"></a> Ns_DString dsLeave;
<a name="16979"></a> CsCtx ctx;
<a name="16980"></a> int status;
<a name="16981"></a>
<a name="16982"></a> Ns_DStringInit(&dsEnter);
<a name="16983"></a> Ns_DStringAppend(&dsEnter, hModule);
<a name="16984"></a> Ns_DStringAppend(&dsEnter, "_enter");
<a name="16985"></a>
<a name="16986"></a> Ns_DStringInit(&dsLeave);
<a name="16987"></a> Ns_DStringAppend(&dsLeave, hModule);
<a name="16988"></a> Ns_DStringAppend(&dsLeave, "_leave");
<a name="16989"></a>
<a name="16990"></a> ctx.enter = dsEnter.string;
<a name="16991"></a> ctx.leave = dsLeave.string;
<a name="16992"></a> ctx.cs = ns_malloc(sizeof(Ns_CriticalSection));
<a name="16993"></a> Ns_InitializeCriticalSection(ctx.cs);
<a name="16994"></a>
<a name="16995"></a> status = Ns_TclInitInterps(hServer, InitCs, (void *) &ctx);
<a name="16996"></a>
<a name="16997"></a> Ns_DStringFree(&dsEnter);
<a name="16998"></a> Ns_DStringFree(&dsLeave);
<a name="16999"></a> return status;
<a name="17000"></a>}
<a name="17001"></a>
<a name="17002"></a>
<a name="17003"></a>/*
<a name="17004"></a> * InitCs - Initialize a single Tcl interpreter with the
<a name="17005"></a> * critical section enter and leave commands.
<a name="17006"></a> */
<a name="17007"></a>static int
<a name="17008"></a>InitCs(Tcl_Interp *interp, void *ctx)
<a name="17009"></a>{
<a name="17010"></a> CsCtx *csctx;
<a name="17011"></a>
<a name="17012"></a> csctx = ctx;
<a name="17013"></a> Tcl_CreateCommand(interp, csctx->enter, EnterCs,
<a name="17063"></a> (ClientData) csctx->cs, NULL);
<a name="17014"></a> Tcl_CreateCommand(interp, csctx->leave, LeaveCs,
<a name="17064"></a> (ClientData) csctx->cs, NULL);
<a name="17015"></a> return TCL_OK;
<a name="17016"></a>}
<a name="17017"></a>
<a name="17018"></a>
<a name="17019"></a>/*
<a name="17020"></a> * EnterCs - Enter the critical section passed in as callback data.
<a name="17021"></a> */
<a name="17022"></a>static int
<a name="17023"></a>EnterCs(ClientData clientData, Tcl_Interp *interp, int argc, char **argv)
<a name="17024"></a>{
<a name="17025"></a> Ns_CriticalSection *cs = (Ns_CriticalSection *) clientData;
<a name="17026"></a>
<a name="17027"></a> Ns_EnterCriticalSection(cs);
<a name="17028"></a> return TCL_OK;
<a name="17029"></a>}
<a name="17030"></a>
<a name="17031"></a>
<a name="17032"></a>/*
<a name="17033"></a> * LeaveCs - Leave the critical section passed in as callback data.
<a name="17034"></a> */
<a name="17035"></a>static int
<a name="17036"></a>LeaveCs(ClientData clientData, Tcl_Interp *interp, int argc, char **argv)
<a name="17037"></a>{
<a name="17038"></a> Ns_CriticalSection *cs = (Ns_CriticalSection *) clientData;
<a name="17039"></a>
<a name="17040"></a> Ns_LeaveCriticalSection(cs);
<a name="17041"></a> return TCL_OK;
<a name="17042"></a>}
</pre><p>
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