共享内存
www.zhaoch.top > 编程 > c_cpp
共享内存的使用
用于在多个进程间快速的传递数据,基本上有两种形式
- mmap
- shmget
以下是nginx为unix族操作系统实现的代码,覆盖了不同的使用形式,使用时可以直接参考。注意NGX_HAVE_MAP_ANON, NGX_HAVE_MAP_DEVZERO, NGX_HAVE_SYSVSHM三个宏
#if (NGX_HAVE_MAP_ANON)
ngx_int_t
ngx_shm_alloc(ngx_shm_t *shm)
{
shm->addr = (u_char *) mmap(NULL, shm->size,
PROT_READ|PROT_WRITE,
MAP_ANON|MAP_SHARED, -1, 0);
if (shm->addr == MAP_FAILED) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"mmap(MAP_ANON|MAP_SHARED, %uz) failed", shm->size);
return NGX_ERROR;
}
return NGX_OK;
}
void
ngx_shm_free(ngx_shm_t *shm)
{
if (munmap((void *) shm->addr, shm->size) == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"munmap(%p, %uz) failed", shm->addr, shm->size);
}
}
#elif (NGX_HAVE_MAP_DEVZERO)
ngx_int_t
ngx_shm_alloc(ngx_shm_t *shm)
{
ngx_fd_t fd;
fd = open("/dev/zero", O_RDWR);
if (fd == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"open(\"/dev/zero\") failed");
return NGX_ERROR;
}
shm->addr = (u_char *) mmap(NULL, shm->size, PROT_READ|PROT_WRITE,
MAP_SHARED, fd, 0);
if (shm->addr == MAP_FAILED) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"mmap(/dev/zero, MAP_SHARED, %uz) failed", shm->size);
}
if (close(fd) == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"close(\"/dev/zero\") failed");
}
return (shm->addr == MAP_FAILED) ? NGX_ERROR : NGX_OK;
}
void
ngx_shm_free(ngx_shm_t *shm)
{
if (munmap((void *) shm->addr, shm->size) == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"munmap(%p, %uz) failed", shm->addr, shm->size);
}
}
#elif (NGX_HAVE_SYSVSHM)
#include <sys/ipc.h>
#include <sys/shm.h>
ngx_int_t
ngx_shm_alloc(ngx_shm_t *shm)
{
int id;
id = shmget(IPC_PRIVATE, shm->size, (SHM_R|SHM_W|IPC_CREAT));
if (id == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"shmget(%uz) failed", shm->size);
return NGX_ERROR;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, shm->log, 0, "shmget id: %d", id);
shm->addr = shmat(id, NULL, 0);
if (shm->addr == (void *) -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno, "shmat() failed");
}
if (shmctl(id, IPC_RMID, NULL) == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"shmctl(IPC_RMID) failed");
}
return (shm->addr == (void *) -1) ? NGX_ERROR : NGX_OK;
}
void
ngx_shm_free(ngx_shm_t *shm)
{
if (shmdt(shm->addr) == -1) {
ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
"shmdt(%p) failed", shm->addr);
}
}
#endif
The End
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