-1
私はpthreadsを初めて使っています。私は、ソートされたファイルにランダムなキーのセットのためのバイナリ検索を実行したスレッドを実行すると、バックキーの値を読んでいます：マルチスレッド読み込み中にfscanfが失敗するのはなぜですか？
int binary_search_in_disk(int k_level, int key){
if (!file_exist(level_fname)){
return -1;
}
char *line = NULL;
size_t len = 0;
ssize_t read;
int num, file_charsize, low_key, mid_key, high_key, value, op;
// file position measured in long int bytes (4), point to the first char of the
// line
int low, mid, high;
FILE* level_file = fopen(level_fname, "r");
printf("fname: %s ,", level_fname);
// find low key
low = 0;
printf("file exists? %d ,", file_exist(level_fname)); // return 1, file exists
num = fscanf(level_file, "%d%d%d\n", &low_key, &value, &op); // seg fault, file does not exist
...
}
私は同じファイルからキーと値のペアを読み込み、別のスレッドを持って、そして破壊しますそのファイルを置き換えて別のファイルの名前を変更します。読み取りと破棄を行う関数にprintfを追加し、printfは、両方のスレッドが読み取り中にsegフォールトが発生することを示します。 GDBはまた、segフォールト時に、両方のスレッドがファイルから読み込んでいることを示しています。プログラムを実行すると、segフォールトは異なる読み込み値で発生します。 level_fileが突然NULLになる原因は何ですか？
GDB：
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb73ffb40 (LWP 13213)]
__isoc99_fscanf (stream=0x0, format=0x804b641 "%d%d%d\n") at isoc99_fscanf.c:30
30 isoc99_fscanf.c: No such file or directory.
(gdb) bt
#0 __isoc99_fscanf (stream=0x0, format=0x804b641 "%d%d%d\n") at isoc99_fscanf.c:30
#1 0x0804ae60 in binary_search_in_disk (k_level=1, key=89) at lib.c:894
#2 0x0804ac04 in search (k_level=1, key=89) at lib.c:809
#3 0x080490da in get (key=89) at lsm.c:56
#4 0x08048dc9 in run_get (args=0x804e0c8) at concurrent_main.c:181
#5 0xb7f71f70 in start_thread (arg=0xb73ffb40) at pthread_create.c:312
#6 0xb7ea7bee in clone() at ../sysdeps/unix/sysv/linux/i386/clone.S:129
(gdb) thread apply all bt
Thread 3 (Thread 0xb73ffb40 (LWP 13213)):
#0 __isoc99_fscanf (stream=0x0, format=0x804b641 "%d%d%d\n") at isoc99_fscanf.c:30
#1 0x0804ae60 in binary_search_in_disk (k_level=1, key=89) at lib.c:894
#2 0x0804ac04 in search (k_level=1, key=89) at lib.c:809
#3 0x080490da in get (key=89) at lsm.c:56
#4 0x08048dc9 in run_get (args=0x804e0c8) at concurrent_main.c:181
#5 0xb7f71f70 in start_thread (arg=0xb73ffb40) at pthread_create.c:312
#6 0xb7ea7bee in clone() at ../sysdeps/unix/sysv/linux/i386/clone.S:129
Thread 2 (Thread 0xb7dbab40 (LWP 13212)):
#0 0xb7fdd428 in __kernel_vsyscall()
#1 0xb7eb5151 in __lll_unlock_wake_private()
at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/lowlevellock.S:349
#2 0xb7e21809 in _L_unlock_156() from /lib/i386-linux-gnu/libc.so.6
#3 0xb7e21768 in _IO_acquire_lock_fct (p=<synthetic pointer>) at libioP.h:905
#4 _IO_puts (str=0x804b738 "Read from disk ... ") at ioputs.c:37
#5 0x0804a39e in merge_in_memory_disk() at lib.c:556
#6 0x080497c7 in lsm_merge (k_level=0) at lib.c:162
#7 0x08049097 in put (key=256, value=256, op=0) at lsm.c:26
#8 0x08048cfa in run_put (args=0x804e028) at concurrent_main.c:128
#9 0xb7f71f70 in start_thread (arg=0xb7dbab40) at pthread_create.c:312
#10 0xb7ea7bee in clone() at ../sysdeps/unix/sysv/linux/i386/clone.S:129
Thread 1 (Thread 0xb7dbb700 (LWP 13208)):
#0 0xb7fdd428 in __kernel_vsyscall()
#1 0xb7f73178 in pthread_join (threadid=3084626752, thread_return=0x0) at pthread_join.c:92
#2 0x08049029 in main (argc=6, argv=0xbfffefd4) at concurrent_main.c:270
(gdb) info threads
Id Target Id Frame
* 3 Thread 0xb73ffb40 (LWP 13213) "concurrent_main" __isoc99_fscanf (stream=0x0,
format=0x804b641 "%d%d%d\n") at isoc99_fscanf.c:30
2 Thread 0xb7dbab40 (LWP 13212) "concurrent_main" 0xb7fdd428 in __kernel_vsyscall()
1 Thread 0xb7dbb700 (LWP 13208) "concurrent_main" 0xb7fdd428 in __kernel_vsyscall()
Valgrindは：
==13748== Thread 3:
==13748== Invalid read of size 4
==13748== at 0x40FE195: __isoc99_fscanf (isoc99_fscanf.c:30)
==13748== by 0x804AE69: binary_search_in_disk (lib.c:892)
==13748== by 0x804AC0D: search (lib.c:809)
==13748== by 0x80490E3: get (lsm.c:56)
==13748== by 0x8048DCD: run_get (concurrent_main.c:183)
==13748== by 0x4092F6F: start_thread (pthread_create.c:312)
==13748== by 0x4193BED: clone (clone.S:129)
==13748== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==13748==
==13748==
==13748== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==13748== Access not within mapped region at address 0x0
==13748== at 0x40FE195: __isoc99_fscanf (isoc99_fscanf.c:30)
==13748== by 0x804AE69: binary_search_in_disk (lib.c:892)
==13748== by 0x804AC0D: search (lib.c:809)
==13748== by 0x80490E3: get (lsm.c:56)
==13748== by 0x8048DCD: run_get (concurrent_main.c:183)
==13748== by 0x4092F6F: start_thread (pthread_create.c:312)
==13748== by 0x4193BED: clone (clone.S:129)
==13748== If you believe this happened as a result of a stack
==13748== overflow in your program's main thread (unlikely but
==13748== possible), you can try to increase the size of the
==13748== main thread stack using the --main-stacksize= flag.
==13748== The main thread stack size used in this run was 8388608.
==13748==
==13748== HEAP SUMMARY:
==13748== in use at exit: 482,004 bytes in 2,046 blocks
==13748== total heap usage: 2,679 allocs, 633 frees, 576,804 bytes allocated
==13748==
==13748== LEAK SUMMARY:
==13748== definitely lost: 122,280 bytes in 1,019 blocks
==13748== indirectly lost: 0 bytes in 0 blocks
==13748== possibly lost: 272 bytes in 2 blocks
==13748== still reachable: 359,452 bytes in 1,025 blocks
==13748== suppressed: 0 bytes in 0 blocks
==13748== Rerun with --leak-check=full to see details of leaked memory
==13748==
==13748== For counts of detected and suppressed errors, rerun with: -v
==13748== Use --track-origins=yes to see where uninitialised values come from
==13748== ERROR SUMMARY: 188 errors from 6 contexts (suppressed: 0 from 0)
Killed