mod_slotmem_shm: Fix balancers and balancer members slots reuse on

restart when new ones are added (Windows and OS/2 only).  PR 58024.

Since Windows and OS/2 don't have the unlink() but the "delete on last close"
semantic for opened files being removed, we can't reuse the same SHM files
names for processes of different generation.  Let's append the generation
number in the files names for those.

This commit also axes unused Unix specifics about mutexes/semaphores.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1702450 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 76 insertions, 57 deletions

diff --git a/modules/slotmem/mod_slotmem_shm.c b/modules/slotmem/mod_slotmem_shm.c
index d010699288..861424d94c 100644
--- a/modules/slotmem/mod_slotmem_shm.c
+++ b/modules/slotmem/mod_slotmem_shm.c
@@ -25,23 +25,6 @@
 
 #include "httpd.h"
 #include "http_main.h"
-#ifdef AP_NEED_SET_MUTEX_PERMS
-#include "unixd.h"
-#endif
-
-#if APR_HAVE_UNISTD_H
-#include <unistd.h>         /* for getpid() */
-#endif
-
-#if HAVE_SYS_SEM_H
-#include <sys/shm.h>
-#if !defined(SHM_R)
-#define SHM_R 0400
-#endif
-#if !defined(SHM_W)
-#define SHM_W 0200
-#endif
-#endif
 
 #define AP_SLOTMEM_IS_PREGRAB(t)    (t->desc.type & AP_SLOTMEM_TYPE_PREGRAB)
 #define AP_SLOTMEM_IS_PERSIST(t)    (t->desc.type & AP_SLOTMEM_TYPE_PERSIST)
@@ -59,6 +42,7 @@ typedef struct {
 
 struct ap_slotmem_instance_t {
     char                 *name;       /* per segment name */
+    char                 *pname;      /* persisted file name */
     int                  fbased;      /* filebased? */
     void                 *shm;        /* ptr to memory segment (apr_shm_t *) */
     void                 *base;       /* data set start */
@@ -86,6 +70,31 @@ static apr_pool_t *gpool = NULL;
 #define DEFAULT_SLOTMEM_SUFFIX ".shm"
 #define DEFAULT_SLOTMEM_PERSIST_SUFFIX ".persist"
 
+/* Unixes (and Netware) have the unlink() semantic, which allows to
+ * apr_file_remove() a file still in use (opened elsewhere), the inode
+ * remains until the last fd is closed, whereas any file created with
+ * the same name/path will use a new inode.
+ *
+ * On windows and OS/2 ("\SHAREMEM\..." tree), apr_file_remove() marks
+ * the files for deletion until the last HANDLE is closed, meanwhile the
+ * same file/path can't be opened/recreated.
+ * Thus on graceful restart (the only restart mode with mpm_winnt), the
+ * old file may still exist until all the children stop, while we ought
+ * to create a new one for our new clear SHM.  Therefore, we would only
+ * be able to reuse (attach) the old SHM, preventing some changes to
+ * the config file, like the number of balancers/members, since the
+ * size checks (to fit the new config) would fail.  Let's avoid this by
+ * including the generation number in the SHM filename (obviously not
+ * the persisted name!)
+ */
+#ifndef SLOTMEM_UNLINK_SEMANTIC
+#if defined(WIN32) || defined(OS2)
+#define SLOTMEM_UNLINK_SEMANTIC 0
+#else
+#define SLOTMEM_UNLINK_SEMANTIC 1
+#endif
+#endif
+
 /*
  * Persist the slotmem in a file
  * slotmem name and file name.
@@ -94,29 +103,49 @@ static apr_pool_t *gpool = NULL;
  * /abs_name : $abs_name
  *
  */
-
-static const char *slotmem_filename(apr_pool_t *pool, const char *slotmemname,
-                                    int persist)
+static int slotmem_filenames(apr_pool_t *pool,
+                             const char *slotname,
+                             const char **filename,
+                             const char **persistname)
 {
-    const char *fname;
-    if (!slotmemname || strcasecmp(slotmemname, "none") == 0) {
-        return NULL;
-    }
-    else if (slotmemname[0] != '/') {
-        const char *filenm = apr_pstrcat(pool, DEFAULT_SLOTMEM_PREFIX,
-                                         slotmemname, DEFAULT_SLOTMEM_SUFFIX,
-                                         NULL);
-        fname = ap_runtime_dir_relative(pool, filenm);
-    }
-    else {
-        fname = slotmemname;
+    const char *fname = NULL, *pname = NULL;
+
+    if (slotname && *slotname && strcasecmp(slotname, "none") != 0) {
+        fname = slotname;
+#if SLOTMEM_UNLINK_SEMANTIC
+        /* Reuse the same file name for each generation. */
+        fname = apr_pstrcat(pool, DEFAULT_SLOTMEM_PREFIX,
+                            fname, DEFAULT_SLOTMEM_SUFFIX,
+                            NULL);
+#else
+        /* Each generation needs its own file name. */
+        fname = apr_psprintf(pool, "%s%s_%x%s", DEFAULT_SLOTMEM_PREFIX,
+                             fname, ap_state_query(AP_SQ_CONFIG_GEN),
+                             DEFAULT_SLOTMEM_SUFFIX);
+#endif
+        fname = ap_runtime_dir_relative(pool, fname);
+
+        if (persistname) {
+            /* Persisted file names are immutable... */
+#if SLOTMEM_UNLINK_SEMANTIC
+            pname = apr_pstrcat(pool, fname,
+                                DEFAULT_SLOTMEM_PERSIST_SUFFIX,
+                                NULL);
+#else
+            pname = apr_pstrcat(pool, DEFAULT_SLOTMEM_PREFIX,
+                                slotname, DEFAULT_SLOTMEM_SUFFIX,
+                                DEFAULT_SLOTMEM_PERSIST_SUFFIX,
+                                NULL);
+            pname = ap_runtime_dir_relative(pool, pname);
+#endif
+        }
     }
 
-    if (persist) {
-        return apr_pstrcat(pool, fname, DEFAULT_SLOTMEM_PERSIST_SUFFIX,
-                           NULL);
+    *filename = fname;
+    if (persistname) {
+        *persistname = pname;
     }
-    return fname;
+    return (fname != NULL);
 }
 
 static void slotmem_clearinuse(ap_slotmem_instance_t *slot)
@@ -143,10 +172,8 @@ static void store_slotmem(ap_slotmem_instance_t *slotmem)
     apr_file_t *fp;
     apr_status_t rv;
     apr_size_t nbytes;
-    const char *storename;
     unsigned char digest[APR_MD5_DIGESTSIZE];
-
-    storename = slotmem_filename(slotmem->gpool, slotmem->name, 1);
+    const char *storename = slotmem->pname;
 
     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf, APLOGNO(02334)
                  "storing %s", storename);
@@ -179,18 +206,15 @@ static void store_slotmem(ap_slotmem_instance_t *slotmem)
     }
 }
 
-static apr_status_t restore_slotmem(void *ptr, const char *name, apr_size_t size,
-                                    apr_pool_t *pool)
+static apr_status_t restore_slotmem(void *ptr, const char *storename,
+                                    apr_size_t size, apr_pool_t *pool)
 {
-    const char *storename;
     apr_file_t *fp;
     apr_size_t nbytes = size;
     apr_status_t rv = APR_SUCCESS;
     unsigned char digest[APR_MD5_DIGESTSIZE];
     unsigned char digest2[APR_MD5_DIGESTSIZE];
 
-    storename = slotmem_filename(pool, name, 1);
-
     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf, APLOGNO(02335)
                  "restoring %s", storename);
 
@@ -247,12 +271,8 @@ static apr_status_t cleanup_slotmem(void *param)
                 store_slotmem(next);
             }
             if (next->fbased) {
-                const char *name;
                 apr_shm_remove(next->name, next->gpool);
-                name = slotmem_filename(next->gpool, next->name, 0);
-                if (name) {
-                    apr_file_remove(name, next->gpool);
-                }
+                apr_file_remove(next->name, next->gpool);
             }
             apr_shm_destroy((apr_shm_t *)next->shm);
             next = next->next;
@@ -295,25 +315,24 @@ static apr_status_t slotmem_create(ap_slotmem_instance_t **new,
                                    unsigned int item_num,
                                    ap_slotmem_type_t type, apr_pool_t *pool)
 {
-/*    void *slotmem = NULL; */
     int fbased = 1;
     int restored = 0;
     char *ptr;
     sharedslotdesc_t desc;
     ap_slotmem_instance_t *res;
     ap_slotmem_instance_t *next = globallistmem;
-    const char *fname;
+    const char *fname, *pname = NULL;
     apr_shm_t *shm;
     apr_size_t basesize = (item_size * item_num);
     apr_size_t size = AP_SLOTMEM_OFFSET + AP_UNSIGNEDINT_OFFSET +
                       (item_num * sizeof(char)) + basesize;
+    int persist = (type & AP_SLOTMEM_TYPE_PERSIST) != 0;
     apr_status_t rv;
 
     if (gpool == NULL) {
         return APR_ENOSHMAVAIL;
     }
-    fname = slotmem_filename(pool, name, 0);
-    if (fname) {
+    if (slotmem_filenames(pool, name, &fname, persist ? &pname : NULL)) {
         /* first try to attach to existing slotmem */
         if (next) {
             for (;;) {
@@ -399,8 +418,8 @@ static apr_status_t slotmem_create(ap_slotmem_instance_t **new,
          * TODO: Error check the below... What error makes
          * sense if the restore fails? Any?
          */
-        if (type & AP_SLOTMEM_TYPE_PERSIST) {
-            rv = restore_slotmem(ptr, fname, dsize, pool);
+        if (persist) {
+            rv = restore_slotmem(ptr, pname, dsize, pool);
             if (rv == APR_SUCCESS) {
                 restored = 1;
             }
@@ -417,6 +436,7 @@ static apr_status_t slotmem_create(ap_slotmem_instance_t **new,
     res = (ap_slotmem_instance_t *) apr_pcalloc(gpool,
                                                 sizeof(ap_slotmem_instance_t));
     res->name = apr_pstrdup(gpool, fname);
+    res->pname = apr_pstrdup(gpool, pname);
     res->fbased = fbased;
     res->shm = shm;
     res->num_free = (unsigned int *)ptr;
@@ -457,8 +477,7 @@ static apr_status_t slotmem_attach(ap_slotmem_instance_t **new,
     if (gpool == NULL) {
         return APR_ENOSHMAVAIL;
     }
-    fname = slotmem_filename(pool, name, 0);
-    if (!fname) {
+    if (!slotmem_filenames(pool, name, &fname, NULL)) {
         return APR_ENOSHMAVAIL;
     }