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25 .TH MALLOC_INFO 3 2013-04-19 "GNU" "Linux Programmer's Manual"
27 malloc_info \- export malloc state to a stream
30 .B #include <malloc.h>
32 .BI "int malloc_info(int " options ", FILE *" fp );
37 function exports an XML string that describes the current state
38 of the memory-allocation
39 implementation in the caller.
40 The string is printed on the file stream
42 The exported string includes information about all arenas (see
45 As currently implemented,
52 on error, it returns \-1, with
54 set to indicate the cause.
62 was added to glibc in version 2.10.
64 This function is a GNU extension.
66 The memory-allocation information is provided as an XML string
67 (rather than a C structure)
68 because the information may change over time
69 (according to changes in the underlying implementation).
70 The output XML string includes a version field.
73 .BR open_memstream (3)
74 function can be used to send the output of
76 directly into a buffer in memory, rather than to a file.
80 function is designed to address deficiencies in
85 The program below takes up to four command-line arguments,
86 of which the first three are mandatory.
87 The first argument specifies the number of threads that
88 the program should create.
89 All of the threads, including the main thread,
90 allocate the number of blocks of memory specified by the second argument.
91 The third argument controls the size of the blocks to be allocated.
92 The main thread creates blocks of this size,
93 the second thread created by the program allocates blocks of twice this size,
94 the third thread allocates blocks of three times this size, and so on.
98 twice to display the memory-allocation state.
99 The first call takes place before any threads
100 are created or memory allocated.
101 The second call is performed after all threads have allocated memory.
103 In the following example,
104 the command-line arguments specify the creation of one additional thread,
105 and both the main thread and the additional thread
106 allocate 10000 blocks of memory.
107 After the blocks of memory have been allocated,
109 shows the state of two allocation arenas.
113 .RB "$ " "getconf GNU_LIBC_VERSION"
115 .RB "$ " "./a.out 1 10000 100"
116 ============ Before allocating blocks ============
121 <total type="fast" count="0" size="0"/>
122 <total type="rest" count="0" size="0"/>
123 <system type="current" size="135168"/>
124 <system type="max" size="135168"/>
125 <aspace type="total" size="135168"/>
126 <aspace type="mprotect" size="135168"/>
128 <total type="fast" count="0" size="0"/>
129 <total type="rest" count="0" size="0"/>
130 <system type="current" size="135168"/>
131 <system type="max" size="135168"/>
132 <aspace type="total" size="135168"/>
133 <aspace type="mprotect" size="135168"/>
136 ============ After allocating blocks ============
141 <total type="fast" count="0" size="0"/>
142 <total type="rest" count="0" size="0"/>
143 <system type="current" size="1081344"/>
144 <system type="max" size="1081344"/>
145 <aspace type="total" size="1081344"/>
146 <aspace type="mprotect" size="1081344"/>
151 <total type="fast" count="0" size="0"/>
152 <total type="rest" count="0" size="0"/>
153 <system type="current" size="1032192"/>
154 <system type="max" size="1032192"/>
155 <aspace type="total" size="1032192"/>
156 <aspace type="mprotect" size="1032192"/>
158 <total type="fast" count="0" size="0"/>
159 <total type="rest" count="0" size="0"/>
160 <system type="current" size="2113536"/>
161 <system type="max" size="2113536"/>
162 <aspace type="total" size="2113536"/>
163 <aspace type="mprotect" size="2113536"/>
176 static size_t blockSize;
177 static int numThreads, numBlocks;
179 #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
183 thread_func(void *arg)
188 /* The multiplier \(aq(2 + tn)\(aq ensures that each thread (including
189 the main thread) allocates a different amount of memory */
191 for (j = 0; j < numBlocks; j++)
192 if (malloc(blockSize * (2 + tn)) == NULL)
193 errExit("malloc\-thread");
195 sleep(100); /* Sleep until main thread terminates */
200 main(int argc, char *argv[])
202 int j, tn, sleepTime;
207 "%s num\-threads num\-blocks block\-size [sleep\-time]\\n",
212 numThreads = atoi(argv[1]);
213 numBlocks = atoi(argv[2]);
214 blockSize = atoi(argv[3]);
215 sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
217 thr = calloc(numThreads, sizeof(pthread_t));
221 printf("============ Before allocating blocks ============\\n");
222 malloc_info(0, stdout);
224 /* Create threads that allocate different amounts of memory */
226 for (tn = 0; tn < numThreads; tn++) {
227 errno = pthread_create(&thr[tn], NULL, thread_func,
230 errExit("pthread_create");
232 /* If we add a sleep interval after the start\-up of each
233 thread, the threads likely won\(aqt contend for malloc
234 mutexes, and therefore additional arenas won\(aqt be
235 allocated (see malloc(3)). */
241 /* The main thread also allocates some memory */
243 for (j = 0; j < numBlocks; j++)
244 if (malloc(blockSize) == NULL)
247 sleep(2); /* Give all threads a chance to
248 complete allocations */
250 printf("\\n============ After allocating blocks ============\\n");
251 malloc_info(0, stdout);
259 .BR malloc_stats (3),
261 .BR open_memstream (3)