Annotation of embedaddon/sqlite3/ext/async/sqlite3async.h, revision 1.1.1.1
1.1 misho 1:
2: #ifndef __SQLITEASYNC_H_
3: #define __SQLITEASYNC_H_ 1
4:
5: /*
6: ** Make sure we can call this stuff from C++.
7: */
8: #ifdef __cplusplus
9: extern "C" {
10: #endif
11:
12: #define SQLITEASYNC_VFSNAME "sqlite3async"
13:
14: /*
15: ** THREAD SAFETY NOTES:
16: **
17: ** Of the four API functions in this file, the following are not threadsafe:
18: **
19: ** sqlite3async_initialize()
20: ** sqlite3async_shutdown()
21: **
22: ** Care must be taken that neither of these functions is called while
23: ** another thread may be calling either any sqlite3async_XXX() function
24: ** or an sqlite3_XXX() API function related to a database handle that
25: ** is using the asynchronous IO VFS.
26: **
27: ** These functions:
28: **
29: ** sqlite3async_run()
30: ** sqlite3async_control()
31: **
32: ** are threadsafe. It is quite safe to call either of these functions even
33: ** if another thread may also be calling one of them or an sqlite3_XXX()
34: ** function related to a database handle that uses the asynchronous IO VFS.
35: */
36:
37: /*
38: ** Initialize the asynchronous IO VFS and register it with SQLite using
39: ** sqlite3_vfs_register(). If the asynchronous VFS is already initialized
40: ** and registered, this function is a no-op. The asynchronous IO VFS
41: ** is registered as "sqlite3async".
42: **
43: ** The asynchronous IO VFS does not make operating system IO requests
44: ** directly. Instead, it uses an existing VFS implementation for all
45: ** required file-system operations. If the first parameter to this function
46: ** is NULL, then the current default VFS is used for IO. If it is not
47: ** NULL, then it must be the name of an existing VFS. In other words, the
48: ** first argument to this function is passed to sqlite3_vfs_find() to
49: ** locate the VFS to use for all real IO operations. This VFS is known
50: ** as the "parent VFS".
51: **
52: ** If the second parameter to this function is non-zero, then the
53: ** asynchronous IO VFS is registered as the default VFS for all SQLite
54: ** database connections within the process. Otherwise, the asynchronous IO
55: ** VFS is only used by connections opened using sqlite3_open_v2() that
56: ** specifically request VFS "sqlite3async".
57: **
58: ** If a parent VFS cannot be located, then SQLITE_ERROR is returned.
59: ** In the unlikely event that operating system specific initialization
60: ** fails (win32 systems create the required critical section and event
61: ** objects within this function), then SQLITE_ERROR is also returned.
62: ** Finally, if the call to sqlite3_vfs_register() returns an error, then
63: ** the error code is returned to the user by this function. In all three
64: ** of these cases, intialization has failed and the asynchronous IO VFS
65: ** is not registered with SQLite.
66: **
67: ** Otherwise, if no error occurs, SQLITE_OK is returned.
68: */
69: int sqlite3async_initialize(const char *zParent, int isDefault);
70:
71: /*
72: ** This function unregisters the asynchronous IO VFS using
73: ** sqlite3_vfs_unregister().
74: **
75: ** On win32 platforms, this function also releases the small number of
76: ** critical section and event objects created by sqlite3async_initialize().
77: */
78: void sqlite3async_shutdown();
79:
80: /*
81: ** This function may only be called when the asynchronous IO VFS is
82: ** installed (after a call to sqlite3async_initialize()). It processes
83: ** zero or more queued write operations before returning. It is expected
84: ** (but not required) that this function will be called by a different
85: ** thread than those threads that use SQLite. The "background thread"
86: ** that performs IO.
87: **
88: ** How many queued write operations are performed before returning
89: ** depends on the global setting configured by passing the SQLITEASYNC_HALT
90: ** verb to sqlite3async_control() (see below for details). By default
91: ** this function never returns - it processes all pending operations and
92: ** then blocks waiting for new ones.
93: **
94: ** If multiple simultaneous calls are made to sqlite3async_run() from two
95: ** or more threads, then the calls are serialized internally.
96: */
97: void sqlite3async_run();
98:
99: /*
100: ** This function may only be called when the asynchronous IO VFS is
101: ** installed (after a call to sqlite3async_initialize()). It is used
102: ** to query or configure various parameters that affect the operation
103: ** of the asynchronous IO VFS. At present there are three parameters
104: ** supported:
105: **
106: ** * The "halt" parameter, which configures the circumstances under
107: ** which the sqlite3async_run() parameter is configured.
108: **
109: ** * The "delay" parameter. Setting the delay parameter to a non-zero
110: ** value causes the sqlite3async_run() function to sleep for the
111: ** configured number of milliseconds between each queued write
112: ** operation.
113: **
114: ** * The "lockfiles" parameter. This parameter determines whether or
115: ** not the asynchronous IO VFS locks the database files it operates
116: ** on. Disabling file locking can improve throughput.
117: **
118: ** This function is always passed two arguments. When setting the value
119: ** of a parameter, the first argument must be one of SQLITEASYNC_HALT,
120: ** SQLITEASYNC_DELAY or SQLITEASYNC_LOCKFILES. The second argument must
121: ** be passed the new value for the parameter as type "int".
122: **
123: ** When querying the current value of a paramter, the first argument must
124: ** be one of SQLITEASYNC_GET_HALT, GET_DELAY or GET_LOCKFILES. The second
125: ** argument to this function must be of type (int *). The current value
126: ** of the queried parameter is copied to the memory pointed to by the
127: ** second argument. For example:
128: **
129: ** int eCurrentHalt;
130: ** int eNewHalt = SQLITEASYNC_HALT_IDLE;
131: **
132: ** sqlite3async_control(SQLITEASYNC_HALT, eNewHalt);
133: ** sqlite3async_control(SQLITEASYNC_GET_HALT, &eCurrentHalt);
134: ** assert( eNewHalt==eCurrentHalt );
135: **
136: ** See below for more detail on each configuration parameter.
137: **
138: ** SQLITEASYNC_HALT:
139: **
140: ** This is used to set the value of the "halt" parameter. The second
141: ** argument must be one of the SQLITEASYNC_HALT_XXX symbols defined
142: ** below (either NEVER, IDLE and NOW).
143: **
144: ** If the parameter is set to NEVER, then calls to sqlite3async_run()
145: ** never return. This is the default setting. If the parameter is set
146: ** to IDLE, then calls to sqlite3async_run() return as soon as the
147: ** queue of pending write operations is empty. If the parameter is set
148: ** to NOW, then calls to sqlite3async_run() return as quickly as
149: ** possible, without processing any pending write requests.
150: **
151: ** If an attempt is made to set this parameter to an integer value other
152: ** than SQLITEASYNC_HALT_NEVER, IDLE or NOW, then sqlite3async_control()
153: ** returns SQLITE_MISUSE and the current value of the parameter is not
154: ** modified.
155: **
156: ** Modifying the "halt" parameter affects calls to sqlite3async_run()
157: ** made by other threads that are currently in progress.
158: **
159: ** SQLITEASYNC_DELAY:
160: **
161: ** This is used to set the value of the "delay" parameter. If set to
162: ** a non-zero value, then after completing a pending write request, the
163: ** sqlite3async_run() function sleeps for the configured number of
164: ** milliseconds.
165: **
166: ** If an attempt is made to set this parameter to a negative value,
167: ** sqlite3async_control() returns SQLITE_MISUSE and the current value
168: ** of the parameter is not modified.
169: **
170: ** Modifying the "delay" parameter affects calls to sqlite3async_run()
171: ** made by other threads that are currently in progress.
172: **
173: ** SQLITEASYNC_LOCKFILES:
174: **
175: ** This is used to set the value of the "lockfiles" parameter. This
176: ** parameter must be set to either 0 or 1. If set to 1, then the
177: ** asynchronous IO VFS uses the xLock() and xUnlock() methods of the
178: ** parent VFS to lock database files being read and/or written. If
179: ** the parameter is set to 0, then these locks are omitted.
180: **
181: ** This parameter may only be set when there are no open database
182: ** connections using the VFS and the queue of pending write requests
183: ** is empty. Attempting to set it when this is not true, or to set it
184: ** to a value other than 0 or 1 causes sqlite3async_control() to return
185: ** SQLITE_MISUSE and the value of the parameter to remain unchanged.
186: **
187: ** If this parameter is set to zero, then it is only safe to access the
188: ** database via the asynchronous IO VFS from within a single process. If
189: ** while writing to the database via the asynchronous IO VFS the database
190: ** is also read or written from within another process, or via another
191: ** connection that does not use the asynchronous IO VFS within the same
192: ** process, the results are undefined (and may include crashes or database
193: ** corruption).
194: **
195: ** Alternatively, if this parameter is set to 1, then it is safe to access
196: ** the database from multiple connections within multiple processes using
197: ** either the asynchronous IO VFS or the parent VFS directly.
198: */
199: int sqlite3async_control(int op, ...);
200:
201: /*
202: ** Values that can be used as the first argument to sqlite3async_control().
203: */
204: #define SQLITEASYNC_HALT 1
205: #define SQLITEASYNC_GET_HALT 2
206: #define SQLITEASYNC_DELAY 3
207: #define SQLITEASYNC_GET_DELAY 4
208: #define SQLITEASYNC_LOCKFILES 5
209: #define SQLITEASYNC_GET_LOCKFILES 6
210:
211: /*
212: ** If the first argument to sqlite3async_control() is SQLITEASYNC_HALT,
213: ** the second argument should be one of the following.
214: */
215: #define SQLITEASYNC_HALT_NEVER 0 /* Never halt (default value) */
216: #define SQLITEASYNC_HALT_NOW 1 /* Halt as soon as possible */
217: #define SQLITEASYNC_HALT_IDLE 2 /* Halt when write-queue is empty */
218:
219: #ifdef __cplusplus
220: } /* End of the 'extern "C"' block */
221: #endif
222: #endif /* ifndef __SQLITEASYNC_H_ */
223:
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