For the unix VFS, avoid an unnecessary stat() system call prior to opening

any file in the common case where there are no unused file descriptors.

FossilOrigin-Name: 3075cfa07489eaf13cb9a2760e2391e79dd73181fe1730fae7bdcd6ad66d2a1f

manifest

@@ -1,5 +1,5 @@
-C Combine\sthe\sOP_CreateTable\sand\sOP_CreateIndex\sopcodes\sof\sthe\sbytecode\sengine\ninto\sa\ssingle\sOP_CreateBtree\sopcode.\s\sThis\ssimplifies\sthe\simplementation\sand\nmakes\sthe\sbytecode\sprograms\sclearer.
+C For\sthe\sunix\sVFS,\savoid\san\sunnecessary\sstat()\ssystem\scall\sprior\sto\sopening\nany\sfile\sin\sthe\scommon\scase\swhere\sthere\sare\sno\sunused\sfile\sdescriptors.
-D 2017-08-18T14:34:28.967
+D 2017-08-18T16:09:52.797
 F Makefile.in d9873c9925917cca9990ee24be17eb9613a668012c85a343aef7e5536ae266e8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 02b469e9dcd5b7ee63fc1fb05babc174260ee4cfa4e0ef2e48c3c6801567a016
@@ -440,7 +440,7 @@ F src/os.c add02933b1dce7a39a005b00a2f5364b763e9a24
 F src/os.h 8e976e59eb4ca1c0fca6d35ee803e38951cb0343
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c a361273749229755f92c8f0e3e4855054ad39bbc5c65773e8db5d0b79afa632c
+F src/os_unix.c 0a7730f6cb797ba1fd12825e4ea751e1325041410c063c258e30089ca71f9a88
 F src/os_win.c 964165b66cde03abc72fe948198b01be608436894732eadb94c8720d2467f223
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 6f2ae58c0d4ddf510d324cb2ec38f471b5cff8f3e061afd32717ad790685cc7f
@@ -1649,7 +1649,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 37e1900880b70be6802eaf43b0e568fda709a1dd6083d8be11e5a7a7d1fda41a
+P eb1202b5e43f1f029ad2bdf845509e7f31361e4dc189943e5e2bd4462e2ef3f3
-R 590c7fe86e3ddb105e4572bf5c63dff2
+R 75fd277ce5c40358998ed365a587d991
 U drh
-Z 553a5b087246c1036f2341d36a71efe3
+Z 8da9bd8ec0af0fa3e80213d960cc13a7

manifest.uuid

@@ -1 +1 @@
-eb1202b5e43f1f029ad2bdf845509e7f31361e4dc189943e5e2bd4462e2ef3f3
+3075cfa07489eaf13cb9a2760e2391e79dd73181fe1730fae7bdcd6ad66d2a1f

src/os_unix.c

@@ -210,7 +210,7 @@ struct unixFile {
   unsigned short int ctrlFlags;       /* Behavioral bits.  UNIXFILE_* flags */
   int lastErrno;                      /* The unix errno from last I/O error */
   void *lockingContext;               /* Locking style specific state */
-  UnixUnusedFd *pUnused;              /* Pre-allocated UnixUnusedFd */
+  UnixUnusedFd *pPreallocatedUnused;  /* Pre-allocated UnixUnusedFd */
   const char *zPath;                  /* Name of the file */
   unixShm *pShm;                      /* Shared memory segment information */
   int szChunk;                        /* Configured by FCNTL_CHUNK_SIZE */
@@ -1120,7 +1120,8 @@ struct unixInodeInfo {
 /*
 ** A lists of all unixInodeInfo objects.
 */
-static unixInodeInfo *inodeList = 0;
+static unixInodeInfo *inodeList = 0;  /* All unixInodeInfo objects */
+static unsigned int nUnusedFd = 0;    /* Total unused file descriptors */
 
 /*
 **
@@ -1230,6 +1231,7 @@ static void closePendingFds(unixFile *pFile){
     pNext = p->pNext;
     robust_close(pFile, p->fd, __LINE__);
     sqlite3_free(p);
+    nUnusedFd--;
   }
   pInode->pUnused = 0;
 }
@@ -1262,6 +1264,7 @@ static void releaseInodeInfo(unixFile *pFile){
       sqlite3_free(pInode);
     }
   }
+  assert( inodeList!=0 || nUnusedFd==0 );
 }
 
 /*
@@ -1331,6 +1334,7 @@ static int findInodeInfo(
 #else
   fileId.ino = (u64)statbuf.st_ino;
 #endif
+  assert( inodeList!=0 || nUnusedFd==0 );
   pInode = inodeList;
   while( pInode && memcmp(&fileId, &pInode->fileId, sizeof(fileId)) ){
     pInode = pInode->pNext;
@@ -1750,11 +1754,12 @@ end_lock:
 */
 static void setPendingFd(unixFile *pFile){
   unixInodeInfo *pInode = pFile->pInode;
-  UnixUnusedFd *p = pFile->pUnused;
+  UnixUnusedFd *p = pFile->pPreallocatedUnused;
   p->pNext = pInode->pUnused;
   pInode->pUnused = p;
   pFile->h = -1;
-  pFile->pUnused = 0;
+  pFile->pPreallocatedUnused = 0;
+  nUnusedFd++;
 }
 
 /*
@@ -1979,7 +1984,7 @@ static int closeUnixFile(sqlite3_file *id){
 #endif
   OSTRACE(("CLOSE   %-3d\n", pFile->h));
   OpenCounter(-1);
-  sqlite3_free(pFile->pUnused);
+  sqlite3_free(pFile->pPreallocatedUnused);
   memset(pFile, 0, sizeof(unixFile));
   return SQLITE_OK;
 }
@@ -3200,7 +3205,7 @@ static int unixRead(
   /* If this is a database file (not a journal, master-journal or temp
   ** file), the bytes in the locking range should never be read or written. */
 #if 0
-  assert( pFile->pUnused==0
+  assert( pFile->pPreallocatedUnused==0
        || offset>=PENDING_BYTE+512
        || offset+amt<=PENDING_BYTE 
   );
@@ -3313,7 +3318,7 @@ static int unixWrite(
   /* If this is a database file (not a journal, master-journal or temp
   ** file), the bytes in the locking range should never be read or written. */
 #if 0
-  assert( pFile->pUnused==0
+  assert( pFile->pPreallocatedUnused==0
        || offset>=PENDING_BYTE+512
        || offset+amt<=PENDING_BYTE 
   );
@@ -5564,6 +5569,8 @@ static UnixUnusedFd *findReusableFd(const char *zPath, int flags){
 #if !OS_VXWORKS
   struct stat sStat;                   /* Results of stat() call */
 
+  unixEnterMutex();
+
   /* A stat() call may fail for various reasons. If this happens, it is
   ** almost certain that an open() call on the same path will also fail.
   ** For this reason, if an error occurs in the stat() call here, it is
@@ -5572,10 +5579,9 @@ static UnixUnusedFd *findReusableFd(const char *zPath, int flags){
   **
   ** Even if a subsequent open() call does succeed, the consequences of
   ** not searching for a reusable file descriptor are not dire.  */
-  if( 0==osStat(zPath, &sStat) ){
+  if( nUnusedFd>0 && 0==osStat(zPath, &sStat) ){
     unixInodeInfo *pInode;
 
-    unixEnterMutex();
     pInode = inodeList;
     while( pInode && (pInode->fileId.dev!=sStat.st_dev
                      || pInode->fileId.ino!=(u64)sStat.st_ino) ){
@@ -5586,11 +5592,12 @@ static UnixUnusedFd *findReusableFd(const char *zPath, int flags){
       for(pp=&pInode->pUnused; *pp && (*pp)->flags!=flags; pp=&((*pp)->pNext));
       pUnused = *pp;
       if( pUnused ){
+        nUnusedFd--;
         *pp = pUnused->pNext;
       }
     }
-    unixLeaveMutex();
   }
+  unixLeaveMutex();
 #endif    /* if !OS_VXWORKS */
   return pUnused;
 }
@@ -5811,7 +5818,7 @@ static int unixOpen(
         return SQLITE_NOMEM_BKPT;
       }
     }
-    p->pUnused = pUnused;
+    p->pPreallocatedUnused = pUnused;
 
     /* Database filenames are double-zero terminated if they are not
     ** URIs with parameters.  Hence, they can always be passed into
@@ -5848,7 +5855,7 @@ static int unixOpen(
     gid_t gid;                    /* Groupid for the file */
     rc = findCreateFileMode(zName, flags, &openMode, &uid, &gid);
     if( rc!=SQLITE_OK ){
-      assert( !p->pUnused );
+      assert( !p->pPreallocatedUnused );
       assert( eType==SQLITE_OPEN_WAL || eType==SQLITE_OPEN_MAIN_JOURNAL );
       return rc;
     }
@@ -5882,9 +5889,9 @@ static int unixOpen(
     *pOutFlags = flags;
   }
 
-  if( p->pUnused ){
+  if( p->pPreallocatedUnused ){
-    p->pUnused->fd = fd;
+    p->pPreallocatedUnused->fd = fd;
-    p->pUnused->flags = flags;
+    p->pPreallocatedUnused->flags = flags;
   }
 
   if( isDelete ){
@@ -5965,7 +5972,7 @@ static int unixOpen(
 
 open_finished:
   if( rc!=SQLITE_OK ){
-    sqlite3_free(p->pUnused);
+    sqlite3_free(p->pPreallocatedUnused);
   }
   return rc;
 }
@@ -6706,7 +6713,7 @@ static int proxyCreateUnixFile(
   dummyVfs.zName = "dummy";
   pUnused->fd = fd;
   pUnused->flags = openFlags;
-  pNew->pUnused = pUnused;
+  pNew->pPreallocatedUnused = pUnused;
   
   rc = fillInUnixFile(&dummyVfs, fd, (sqlite3_file*)pNew, path, 0);
   if( rc==SQLITE_OK ){