summaryrefslogtreecommitdiffstats
path: root/generic/tclThreadStorage.c
blob: b2de9b4528853b5900cb0019842f2ff012727231 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
/*
 * tclThreadStorage.c --
 *
 *	This file implements platform independent thread storage operations to
 *	work around system limits on the number of thread-specific variables.
 *
 * Copyright © 2003-2004 Joe Mistachkin
 * Copyright © 2008 George Peter Staplin
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

#if TCL_THREADS
#include <signal.h>

/*
 * IMPLEMENTATION NOTES:
 *
 * The primary idea is that we create one platform-specific TSD slot, and use
 * it for storing a table pointer. Each Tcl_ThreadDataKey has an offset into
 * the table of TSD values. We don't use more than 1 platform-specific TSD
 * slot, because there is a hard limit on the number of TSD slots. Valid key
 * offsets are greater than 0; 0 is for the initialized Tcl_ThreadDataKey.
 */

/*
 * The global collection of information about TSDs. This is shared across the
 * whole process, and includes the mutex used to protect it.
 */

static struct {
    void *key;			/* Key into the system TSD structure. The
				 * collection of Tcl TSD values for a
				 * particular thread will hang off the
				 * back-end of this. */
    sig_atomic_t counter;	/* The number of different Tcl TSDs used
				 * across *all* threads. This is a strictly
				 * increasing value. */
    Tcl_Mutex mutex;		/* Protection for the rest of this structure,
				 * which holds per-process data. */
} tsdGlobal = { NULL, 0, NULL };

/*
 * The type of the data held per thread in a system TSD.
 */

typedef struct {
    ClientData *tablePtr;	/* The table of Tcl TSDs. */
    sig_atomic_t allocated;	/* The size of the table in the current
				 * thread. */
} TSDTable;

/*
 * The actual type of Tcl_ThreadDataKey.
 */

typedef union {
    volatile sig_atomic_t offset;
				/* The type is really an offset into the
				 * thread-local table of TSDs, which is this
				 * field. */
    void *ptr;			/* For alignment purposes only. Not actually
				 * accessed through this. */
} TSDUnion;

/*
 * Forward declarations of functions in this file.
 */

static TSDTable *	TSDTableCreate(void);
static void		TSDTableDelete(TSDTable *tsdTablePtr);
static void		TSDTableGrow(TSDTable *tsdTablePtr,
			    sig_atomic_t atLeast);

/*
 * Allocator and deallocator for a TSDTable structure.
 */

static TSDTable *
TSDTableCreate(void)
{
    TSDTable *tsdTablePtr;
    sig_atomic_t i;

    tsdTablePtr = (TSDTable *)TclpSysAlloc(sizeof(TSDTable), 0);
    if (tsdTablePtr == NULL) {
	Tcl_Panic("unable to allocate TSDTable");
    }

    tsdTablePtr->allocated = 8;
    tsdTablePtr->tablePtr =
	    (void **)TclpSysAlloc(sizeof(void *) * tsdTablePtr->allocated, 0);
    if (tsdTablePtr->tablePtr == NULL) {
	Tcl_Panic("unable to allocate TSDTable");
    }

    for (i = 0; i < tsdTablePtr->allocated; ++i) {
	tsdTablePtr->tablePtr[i] = NULL;
    }

    return tsdTablePtr;
}

static void
TSDTableDelete(
    TSDTable *tsdTablePtr)
{
    sig_atomic_t i;

    for (i=0 ; i<tsdTablePtr->allocated ; i++) {
	if (tsdTablePtr->tablePtr[i] != NULL) {
	    /*
	     * These values were allocated in Tcl_GetThreadData in tclThread.c
	     * and must now be deallocated or they will leak.
	     */

	    ckfree(tsdTablePtr->tablePtr[i]);
	}
    }

    TclpSysFree(tsdTablePtr->tablePtr);
    TclpSysFree(tsdTablePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TSDTableGrow --
 *
 *	This procedure makes the passed TSDTable grow to fit the atLeast
 *	value.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The table is enlarged.
 *
 *----------------------------------------------------------------------
 */

static void
TSDTableGrow(
    TSDTable *tsdTablePtr,
    sig_atomic_t atLeast)
{
    sig_atomic_t newAllocated = tsdTablePtr->allocated * 2;
    void **newTablePtr;
    sig_atomic_t i;

    if (newAllocated <= atLeast) {
	newAllocated = atLeast + 10;
    }

    newTablePtr = (void **)TclpSysRealloc(tsdTablePtr->tablePtr,
	    sizeof(void *) * newAllocated);
    if (newTablePtr == NULL) {
	Tcl_Panic("unable to reallocate TSDTable");
    }

    for (i = tsdTablePtr->allocated; i < newAllocated; ++i) {
	newTablePtr[i] = NULL;
    }

    tsdTablePtr->allocated = newAllocated;
    tsdTablePtr->tablePtr = newTablePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TclThreadStorageKeyGet --
 *
 *    This procedure gets the value associated with the passed key.
 *
 * Results:
 *	A pointer value associated with the Tcl_ThreadDataKey or NULL.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

void *
TclThreadStorageKeyGet(
    Tcl_ThreadDataKey *dataKeyPtr)
{
    TSDTable *tsdTablePtr = (TSDTable *)TclpThreadGetGlobalTSD(tsdGlobal.key);
    ClientData resultPtr = NULL;
    TSDUnion *keyPtr = (TSDUnion *) dataKeyPtr;
    sig_atomic_t offset = keyPtr->offset;

    if ((tsdTablePtr != NULL) && (offset > 0)
	    && (offset < tsdTablePtr->allocated)) {
	resultPtr = tsdTablePtr->tablePtr[offset];
    }
    return resultPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TclThreadStorageKeySet --
 *
 *	This procedure set an association of value with the key passed. The
 *	associated value may be retrieved with TclThreadDataKeyGet().
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The thread-specific table may be created or reallocated.
 *
 *----------------------------------------------------------------------
 */

void
TclThreadStorageKeySet(
    Tcl_ThreadDataKey *dataKeyPtr,
    void *value)
{
    TSDTable *tsdTablePtr = (TSDTable *)TclpThreadGetGlobalTSD(tsdGlobal.key);
    TSDUnion *keyPtr = (TSDUnion *) dataKeyPtr;

    if (tsdTablePtr == NULL) {
	tsdTablePtr = TSDTableCreate();
	TclpThreadSetGlobalTSD(tsdGlobal.key, tsdTablePtr);
    }

    /*
     * Get the lock while we check if this TSD is new or not. Note that this
     * is the only place where Tcl_ThreadDataKey values are set. We use a
     * double-checked lock to try to avoid having to grab this lock a lot,
     * since it is on quite a few critical paths and will only get set once in
     * each location.
     */

    if (keyPtr->offset == 0) {
	Tcl_MutexLock(&tsdGlobal.mutex);
	if (keyPtr->offset == 0) {
	    /*
	     * The Tcl_ThreadDataKey hasn't been used yet. Make a new one.
	     */

	    keyPtr->offset = ++tsdGlobal.counter;
	}
	Tcl_MutexUnlock(&tsdGlobal.mutex);
    }

    /*
     * Check if this is the first time this Tcl_ThreadDataKey has been used
     * with the current thread. Note that we don't need to hold a lock when
     * doing this, as we are *definitely* the only point accessing this
     * tsdTablePtr right now; it's thread-local.
     */

    if (keyPtr->offset >= tsdTablePtr->allocated) {
	TSDTableGrow(tsdTablePtr, keyPtr->offset);
    }

    /*
     * Set the value in the Tcl thread-local variable.
     */

    tsdTablePtr->tablePtr[keyPtr->offset] = value;
}

/*
 *----------------------------------------------------------------------
 *
 * TclFinalizeThreadDataThread --
 *
 *	This procedure finalizes the data for a single thread.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The TSDTable is deleted/freed.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeThreadDataThread(void)
{
    TSDTable *tsdTablePtr = (TSDTable *)TclpThreadGetGlobalTSD(tsdGlobal.key);

    if (tsdTablePtr != NULL) {
	TSDTableDelete(tsdTablePtr);
	TclpThreadSetGlobalTSD(tsdGlobal.key, NULL);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclInitializeThreadStorage --
 *
 *	This procedure initializes the TSD subsystem with per-platform code.
 *	This should be called before any Tcl threads are created.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Allocates a system TSD.
 *
 *----------------------------------------------------------------------
 */

void
TclInitThreadStorage(void)
{
    tsdGlobal.key = TclpThreadCreateKey();
}

/*
 *----------------------------------------------------------------------
 *
 * TclFinalizeThreadStorage --
 *
 *	This procedure cleans up the thread storage data key for all threads.
 *	IMPORTANT: All Tcl threads must be finalized before calling this!
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Releases the thread data key.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeThreadStorage(void)
{
    TclpThreadDeleteKey(tsdGlobal.key);
    tsdGlobal.key = NULL;
}

#else /* !TCL_THREADS */
/*
 * Stub functions for non-threaded builds
 */

void
TclInitThreadStorage(void)
{
}

void
TclFinalizeThreadDataThread(void)
{
}

void
TclFinalizeThreadStorage(void)
{
}
#endif /* TCL_THREADS */

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */