The X Libraries should be built thread-safe.
The behaviour of the interfaces in this library is specified by the following Standards.
| X11R6.4 Xlib - C library[1] |
Table 12-2. libX11 - X Windows Interface Function Interfaces
| XActivateScreenSaver[1] | XEmptyRegion[1] | XOpenDisplay[1] | XTextWidth16[1] | XkbFreeCompatMap[1] |
| XAddConnectionWatch[1] | XEnableAccessControl[1] | XOpenIM[1] | XTranslateCoordinates[1] | XkbFreeComponentList[1] |
| XAddExtension[1] | XEqualRegion[1] | XOpenOM[1] | XUndefineCursor[1] | XkbFreeControls[1] |
| XAddHost[1] | XEventMaskOfScreen[1] | XParseColor[1] | XUngrabButton[1] | XkbFreeGeomColors[1] |
| XAddHosts[1] | XEventsQueued[1] | XParseGeometry[1] | XUngrabKey[1] | XkbFreeGeomDoodads[1] |
| XAddPixel[1] | XExtendedMaxRequestSize[1] | XPeekEvent[1] | XUngrabKeyboard[1] | XkbFreeGeomKeyAliases[1] |
| XAddToExtensionList[1] | XExtentsOfFontSet[1] | XPeekIfEvent[1] | XUngrabPointer[1] | XkbFreeGeomKeys[1] |
| XAddToSaveSet[1] | XFetchBuffer[1] | XPending[1] | XUngrabServer[1] | XkbFreeGeomOutlines[1] |
| XAllPlanes[1] | XFetchBytes[1] | XPlanesOfScreen[1] | XUninstallColormap[1] | XkbFreeGeomOverlayKeys[1] |
| XAllocClassHint[1] | XFetchName[1] | XPointInRegion[1] | XUnionRectWithRegion[1] | XkbFreeGeomOverlayRows[1] |
| XAllocColor[1] | XFillArc[1] | XPolygonRegion[1] | XUnionRegion[1] | XkbFreeGeomOverlays[1] |
| XAllocColorCells[1] | XFillArcs[1] | XProcessInternalConnection[1] | XUnloadFont[1] | XkbFreeGeomPoints[1] |
| XAllocColorPlanes[1] | XFillPolygon[1] | XProtocolRevision[1] | XUnlockDisplay[1] | XkbFreeGeomProperties[1] |
| XAllocIconSize[1] | XFillRectangle[1] | XProtocolVersion[1] | XUnmapSubwindows[1] | XkbFreeGeomRows[1] |
| XAllocNamedColor[1] | XFillRectangles[1] | XPutBackEvent[1] | XUnmapWindow[1] | XkbFreeGeomSections[1] |
| XAllocSizeHints[1] | XFilterEvent[1] | XPutImage[1] | XUnregisterIMInstantiateCallback[1] | XkbFreeGeomShapes[1] |
| XAllocStandardColormap[1] | XFindContext[1] | XPutPixel[1] | XUnsetICFocus[1] | XkbFreeGeometry[1] |
| XAllocWMHints[1] | XFindOnExtensionList[1] | XQLength[1] | XVaCreateNestedList[1] | XkbFreeIndicatorMaps[1] |
| XAllowEvents[1] | XFlush[1] | XQueryBestCursor[1] | XVendorRelease[1] | XkbFreeKeyboard[1] |
| XAutoRepeatOff[1] | XFlushGC[1] | XQueryBestSize[1] | XVisualIDFromVisual[1] | XkbFreeNames[1] |
| XAutoRepeatOn[1] | XFontsOfFontSet[1] | XQueryBestStipple[1] | XWMGeometry[1] | XkbFreeServerMap[1] |
| XBaseFontNameListOfFontSet[1] | XForceScreenSaver[1] | XQueryBestTile[1] | XWarpPointer[1] | XkbGetAutoRepeatRate[1] |
| XBell[1] | XFree[1] | XQueryColor[1] | XWhitePixel[1] | XkbGetCompatMap[1] |
| XBitmapBitOrder[1] | XFreeColormap[1] | XQueryColors[1] | XWhitePixelOfScreen[1] | XkbGetControls[1] |
| XBitmapPad[1] | XFreeColors[1] | XQueryExtension[1] | XWidthMMOfScreen[1] | XkbGetGeometry[1] |
| XBitmapUnit[1] | XFreeCursor[1] | XQueryFont[1] | XWidthOfScreen[1] | XkbGetIndicatorMap[1] |
| XBlackPixel[1] | XFreeExtensionList[1] | XQueryKeymap[1] | XWindowEvent[1] | XkbGetIndicatorState[1] |
| XBlackPixelOfScreen[1] | XFreeFont[1] | XQueryPointer[1] | XWithdrawWindow[1] | XkbGetKeyActions[1] |
| XCellsOfScreen[1] | XFreeFontInfo[1] | XQueryTextExtents[1] | XWriteBitmapFile[1] | XkbGetKeyBehaviors[1] |
| XChangeActivePointerGrab[1] | XFreeFontNames[1] | XQueryTextExtents16[1] | XXorRegion[1] | XkbGetKeyExplicitComponents[1] |
| XChangeGC[1] | XFreeFontPath[1] | XQueryTree[1] | XauDisposeAuth[1] | XkbGetKeyModifierMap[1] |
| XChangeKeyboardControl[1] | XFreeFontSet[1] | XRaiseWindow[1] | XauFileName[1] | XkbGetKeySyms[1] |
| XChangeKeyboardMapping[1] | XFreeGC[1] | XReadBitmapFile[1] | XauGetBestAuthByAddr[1] | XkbGetKeyTypes[1] |
| XChangePointerControl[1] | XFreeModifiermap[1] | XReadBitmapFileData[1] | XauReadAuth[1] | XkbGetKeyVirtualModMap[1] |
| XChangeProperty[1] | XFreePixmap[1] | XRebindKeysym[1] | XcmsAddColorSpace[1] | XkbGetKeyboard[1] |
| XChangeSaveSet[1] | XFreeStringList[1] | XRecolorCursor[1] | XcmsAddFunctionSet[1] | XkbGetKeyboardByName[1] |
| XChangeWindowAttributes[1] | XGContextFromGC[1] | XReconfigureWMWindow[1] | XcmsAllocColor[1] | XkbGetMap[1] |
| XCheckIfEvent[1] | XGeometry[1] | XRectInRegion[1] | XcmsAllocNamedColor[1] | XkbGetMapChanges[1] |
| XCheckMaskEvent[1] | XGetAtomName[1] | XRefreshKeyboardMapping[1] | XcmsCCCOfColormap[1] | XkbGetNamedGeometry[1] |
| XCheckTypedEvent[1] | XGetAtomNames[1] | XRegisterIMInstantiateCallback[1] | XcmsCIELabClipL[1] | XkbGetNamedIndicator[1] |
| XCheckTypedWindowEvent[1] | XGetClassHint[1] | XRemoveConnectionWatch[1] | XcmsCIELabClipLab[1] | XkbGetNames[1] |
| XCheckWindowEvent[1] | XGetCommand[1] | XRemoveFromSaveSet[1] | XcmsCIELabClipab[1] | XkbGetState[1] |
| XCirculateSubwindows[1] | XGetDefault[1] | XRemoveHost[1] | XcmsCIELabQueryMaxC[1] | XkbGetUpdatedMap[1] |
| XCirculateSubwindowsDown[1] | XGetErrorDatabaseText[1] | XRemoveHosts[1] | XcmsCIELabQueryMaxL[1] | XkbGetVirtualMods[1] |
| XCirculateSubwindowsUp[1] | XGetErrorText[1] | XReparentWindow[1] | XcmsCIELabQueryMaxLC[1] | XkbGetXlibControls[1] |
| XClearArea[1] | XGetFontPath[1] | XResetScreenSaver[1] | XcmsCIELabQueryMinL[1] | XkbIgnoreExtension[1] |
| XClearWindow[1] | XGetFontProperty[1] | XResizeWindow[1] | XcmsCIELabToCIEXYZ[1] | XkbInitCanonicalKeyTypes[1] |
| XClipBox[1] | XGetGCValues[1] | XResourceManagerString[1] | XcmsCIELabWhiteShiftColors[1] | XkbKeyTypesForCoreSymbols[1] |
| XCloseDisplay[1] | XGetGeometry[1] | XRestackWindows[1] | XcmsCIELuvClipL[1] | XkbKeycodeToKeysym[1] |
| XCloseIM[1] | XGetICValues[1] | XRootWindow[1] | XcmsCIELuvClipLuv[1] | XkbKeysymToModifiers[1] |
| XCloseOM[1] | XGetIMValues[1] | XRootWindowOfScreen[1] | XcmsCIELuvClipuv[1] | XkbLatchGroup[1] |
| XConfigureWindow[1] | XGetIconName[1] | XRotateBuffers[1] | XcmsCIELuvQueryMaxC[1] | XkbLatchModifiers[1] |
| XConnectionNumber[1] | XGetIconSizes[1] | XRotateWindowProperties[1] | XcmsCIELuvQueryMaxL[1] | XkbLibraryVersion[1] |
| XContextDependentDrawing[1] | XGetImage[1] | XSaveContext[1] | XcmsCIELuvQueryMaxLC[1] | XkbListComponents[1] |
| XContextualDrawing[1] | XGetInputFocus[1] | XScreenCount[1] | XcmsCIELuvQueryMinL[1] | XkbLockGroup[1] |
| XConvertCase[1] | XGetKeyboardControl[1] | XScreenNumberOfScreen[1] | XcmsCIELuvToCIEuvY[1] | XkbLockModifiers[1] |
| XConvertSelection[1] | XGetKeyboardMapping[1] | XScreenOfDisplay[1] | XcmsCIELuvWhiteShiftColors[1] | XkbLookupKeyBinding[1] |
| XCopyArea[1] | XGetModifierMapping[1] | XScreenResourceString[1] | XcmsCIEXYZToCIELab[1] | XkbLookupKeySym[1] |
| XCopyColormapAndFree[1] | XGetMotionEvents[1] | XSelectInput[1] | XcmsCIEXYZToCIEuvY[1] | XkbNoteControlsChanges[1] |
| XCopyGC[1] | XGetNormalHints[1] | XSendEvent[1] | XcmsCIEXYZToCIExyY[1] | XkbNoteMapChanges[1] |
| XCopyPlane[1] | XGetOCValues[1] | XServerVendor[1] | XcmsCIEXYZToRGBi[1] | XkbNoteNameChanges[1] |
| XCreateBitmapFromData[1] | XGetOMValues[1] | XSetAccessControl[1] | XcmsCIEuvYToCIELuv[1] | XkbOpenDisplay[1] |
| XCreateColormap[1] | XGetPixel[1] | XSetAfterFunction[1] | XcmsCIEuvYToCIEXYZ[1] | XkbQueryExtension[1] |
| XCreateFontCursor[1] | XGetPointerControl[1] | XSetArcMode[1] | XcmsCIEuvYToTekHVC[1] | XkbRefreshKeyboardMapping[1] |
| XCreateFontSet[1] | XGetPointerMapping[1] | XSetAuthorization[1] | XcmsCIExyYToCIEXYZ[1] | XkbResizeKeyActions[1] |
| XCreateGC[1] | XGetRGBColormaps[1] | XSetBackground[1] | XcmsClientWhitePointOfCCC[1] | XkbResizeKeySyms[1] |
| XCreateGlyphCursor[1] | XGetScreenSaver[1] | XSetClassHint[1] | XcmsConvertColors[1] | XkbResizeKeyType[1] |
| XCreateIC[1] | XGetSelectionOwner[1] | XSetClipMask[1] | XcmsCreateCCC[1] | XkbSelectEventDetails[1] |
| XCreateImage[1] | XGetSizeHints[1] | XSetClipOrigin[1] | XcmsDefaultCCC[1] | XkbSelectEvents[1] |
| XCreateOC[1] | XGetStandardColormap[1] | XSetClipRectangles[1] | XcmsDisplayOfCCC[1] | XkbSetAtomFuncs[1] |
| XCreatePixmap[1] | XGetSubImage[1] | XSetCloseDownMode[1] | XcmsFormatOfPrefix[1] | XkbSetAutoRepeatRate[1] |
| XCreatePixmapCursor[1] | XGetTextProperty[1] | XSetCommand[1] | XcmsFreeCCC[1] | XkbSetAutoResetControls[1] |
| XCreatePixmapFromBitmapData[1] | XGetTransientForHint[1] | XSetDashes[1] | XcmsLookupColor[1] | XkbSetCompatMap[1] |
| XCreateRegion[1] | XGetVisualInfo[1] | XSetErrorHandler[1] | XcmsPrefixOfFormat[1] | XkbSetControls[1] |
| XCreateSimpleWindow[1] | XGetWMClientMachine[1] | XSetFillRule[1] | XcmsQueryBlack[1] | XkbSetDebuggingFlags[1] |
| XCreateWindow[1] | XGetWMColormapWindows[1] | XSetFillStyle[1] | XcmsQueryBlue[1] | XkbSetDetectableAutoRepeat[1] |
| XDefaultColormap[1] | XGetWMHints[1] | XSetFont[1] | XcmsQueryColor[1] | XkbSetGeometry[1] |
| XDefaultColormapOfScreen[1] | XGetWMIconName[1] | XSetFontPath[1] | XcmsQueryColors[1] | XkbSetIgnoreLockMods[1] |
| XDefaultDepth[1] | XGetWMName[1] | XSetForeground[1] | XcmsQueryGreen[1] | XkbSetIndicatorMap[1] |
| XDefaultDepthOfScreen[1] | XGetWMNormalHints[1] | XSetFunction[1] | XcmsQueryRed[1] | XkbSetMap[1] |
| XDefaultGC[1] | XGetWMProtocols[1] | XSetGraphicsExposures[1] | XcmsQueryWhite[1] | XkbSetNamedIndicator[1] |
| XDefaultGCOfScreen[1] | XGetWMSizeHints[1] | XSetICFocus[1] | XcmsRGBToRGBi[1] | XkbSetNames[1] |
| XDefaultRootWindow[1] | XGetWindowAttributes[1] | XSetICValues[1] | XcmsRGBiToCIEXYZ[1] | XkbSetServerInternalMods[1] |
| XDefaultScreen[1] | XGetWindowProperty[1] | XSetIMValues[1] | XcmsRGBiToRGB[1] | XkbSetXlibControls[1] |
| XDefaultScreenOfDisplay[1] | XGetZoomHints[1] | XSetIOErrorHandler[1] | XcmsScreenNumberOfCCC[1] | XkbToControl[1] |
| XDefaultString[1] | XGrabButton[1] | XSetIconName[1] | XcmsScreenWhitePointOfCCC[1] | XkbTranslateKey[1] |
| XDefaultVisual[1] | XGrabKey[1] | XSetIconSizes[1] | XcmsSetCCCOfColormap[1] | XkbTranslateKeyCode[1] |
| XDefaultVisualOfScreen[1] | XGrabKeyboard[1] | XSetInputFocus[1] | XcmsSetCompressionProc[1] | XkbTranslateKeySym[1] |
| XDefineCursor[1] | XGrabPointer[1] | XSetLineAttributes[1] | XcmsSetWhiteAdjustProc[1] | XkbUpdateActionVirtualMods[1] |
| XDeleteContext[1] | XGrabServer[1] | XSetLocaleModifiers[1] | XcmsSetWhitePoint[1] | XkbUpdateKeyTypeVirtualMods[1] |
| XDeleteModifiermapEntry[1] | XHeightMMOfScreen[1] | XSetModifierMapping[1] | XcmsStoreColor[1] | XkbUpdateMapFromCore[1] |
| XDeleteProperty[1] | XHeightOfScreen[1] | XSetNormalHints[1] | XcmsStoreColors[1] | XkbUseExtension[1] |
| XDestroyIC[1] | XIMOfIC[1] | XSetOCValues[1] | XcmsTekHVCClipC[1] | XkbVirtualModsToReal[1] |
| XDestroyImage[1] | XIconifyWindow[1] | XSetOMValues[1] | XcmsTekHVCClipV[1] | XkbXlibControlsImplemented[1] |
| XDestroyOC[1] | XIfEvent[1] | XSetPlaneMask[1] | XcmsTekHVCClipVC[1] | XmbDrawImageString[1] |
| XDestroyRegion[1] | XImageByteOrder[1] | XSetPointerMapping[1] | XcmsTekHVCQueryMaxC[1] | XmbDrawString[1] |
| XDestroySubwindows[1] | XInitExtension[1] | XSetRGBColormaps[1] | XcmsTekHVCQueryMaxV[1] | XmbDrawText[1] |
| XDestroyWindow[1] | XInitImage[1] | XSetRegion[1] | XcmsTekHVCQueryMaxVC[1] | XmbLookupString[1] |
| XDirectionalDependentDrawing[1] | XInitThreads[1] | XSetScreenSaver[1] | XcmsTekHVCQueryMaxVSamples[1] | XmbResetIC[1] |
| XDisableAccessControl[1] | XInsertModifiermapEntry[1] | XSetSelectionOwner[1] | XcmsTekHVCQueryMinV[1] | XmbSetWMProperties[1] |
| XDisplayCells[1] | XInstallColormap[1] | XSetSizeHints[1] | XcmsTekHVCToCIEuvY[1] | XmbTextEscapement[1] |
| XDisplayHeight[1] | XInternAtom[1] | XSetStandardColormap[1] | XcmsTekHVCWhiteShiftColors[1] | XmbTextExtents[1] |
| XDisplayHeightMM[1] | XInternAtoms[1] | XSetStandardProperties[1] | XcmsVisualOfCCC[1] | XmbTextListToTextProperty[1] |
| XDisplayKeycodes[1] | XInternalConnectionNumbers[1] | XSetState[1] | XkbAllocClientMap[1] | XmbTextPerCharExtents[1] |
| XDisplayMotionBufferSize[1] | XIntersectRegion[1] | XSetStipple[1] | XkbAllocCompatMap[1] | XmbTextPropertyToTextList[1] |
| XDisplayName[1] | XKeycodeToKeysym[1] | XSetSubwindowMode[1] | XkbAllocControls[1] | XrmCombineDatabase[1] |
| XDisplayOfIM[1] | XKeysymToKeycode[1] | XSetTSOrigin[1] | XkbAllocGeomColors[1] | XrmCombineFileDatabase[1] |
| XDisplayOfOM[1] | XKeysymToString[1] | XSetTextProperty[1] | XkbAllocGeomDoodads[1] | XrmDestroyDatabase[1] |
| XDisplayOfScreen[1] | XKillClient[1] | XSetTile[1] | XkbAllocGeomKeyAliases[1] | XrmEnumerateDatabase[1] |
| XDisplayPlanes[1] | XLastKnownRequestProcessed[1] | XSetTransientForHint[1] | XkbAllocGeomKeys[1] | XrmGetDatabase[1] |
| XDisplayString[1] | XListDepths[1] | XSetWMClientMachine[1] | XkbAllocGeomOutlines[1] | XrmGetFileDatabase[1] |
| XDisplayWidth[1] | XListExtensions[1] | XSetWMColormapWindows[1] | XkbAllocGeomOverlayKeys[1] | XrmGetResource[1] |
| XDisplayWidthMM[1] | XListFonts[1] | XSetWMHints[1] | XkbAllocGeomOverlayRows[1] | XrmGetStringDatabase[1] |
| XDoesBackingStore[1] | XListFontsWithInfo[1] | XSetWMIconName[1] | XkbAllocGeomOverlays[1] | XrmInitialize[1] |
| XDoesSaveUnders[1] | XListHosts[1] | XSetWMName[1] | XkbAllocGeomPoints[1] | XrmLocaleOfDatabase[1] |
| XDrawArc[1] | XListInstalledColormaps[1] | XSetWMNormalHints[1] | XkbAllocGeomProps[1] | XrmMergeDatabases[1] |
| XDrawArcs[1] | XListPixmapFormats[1] | XSetWMProperties[1] | XkbAllocGeomRows[1] | XrmParseCommand[1] |
| XDrawImageString[1] | XListProperties[1] | XSetWMProtocols[1] | XkbAllocGeomSectionDoodads[1] | XrmPermStringToQuark[1] |
| XDrawImageString16[1] | XLoadFont[1] | XSetWMSizeHints[1] | XkbAllocGeomSections[1] | XrmPutFileDatabase[1] |
| XDrawLine[1] | XLoadQueryFont[1] | XSetWindowBackground[1] | XkbAllocGeomShapes[1] | XrmPutLineResource[1] |
| XDrawLines[1] | XLocaleOfFontSet[1] | XSetWindowBackgroundPixmap[1] | XkbAllocGeometry[1] | XrmPutResource[1] |
| XDrawPoint[1] | XLocaleOfIM[1] | XSetWindowBorder[1] | XkbAllocIndicatorMaps[1] | XrmPutStringResource[1] |
| XDrawPoints[1] | XLocaleOfOM[1] | XSetWindowBorderPixmap[1] | XkbAllocKeyboard[1] | XrmQGetResource[1] |
| XDrawRectangle[1] | XLockDisplay[1] | XSetWindowBorderWidth[1] | XkbAllocNames[1] | XrmQGetSearchList[1] |
| XDrawRectangles[1] | XLookupColor[1] | XSetWindowColormap[1] | XkbAllocServerMap[1] | XrmQGetSearchResource[1] |
| XDrawSegments[1] | XLookupKeysym[1] | XSetZoomHints[1] | XkbApplyCompatMapToKey[1] | XrmQPutResource[1] |
| XDrawString[1] | XLookupString[1] | XShrinkRegion[1] | XkbApplyVirtualModChanges[1] | XrmQPutStringResource[1] |
| XDrawString16[1] | XLowerWindow[1] | XStoreBuffer[1] | XkbBell[1] | XrmQuarkToString[1] |
| XDrawText[1] | XMapRaised[1] | XStoreBytes[1] | XkbBellEvent[1] | XrmSetDatabase[1] |
| XDrawText16[1] | XMapSubwindows[1] | XStoreColor[1] | XkbChangeEnabledControls[1] | XrmStringToBindingQuarkList[1] |
| XEHeadOfExtensionList[1] | XMapWindow[1] | XStoreColors[1] | XkbChangeKeycodeRange[1] | XrmStringToQuark[1] |
| XESetBeforeFlush[1] | XMaskEvent[1] | XStoreName[1] | XkbChangeMap[1] | XrmStringToQuarkList[1] |
| XESetCloseDisplay[1] | XMatchVisualInfo[1] | XStoreNamedColor[1] | XkbChangeNames[1] | XrmUniqueQuark[1] |
| XESetCopyGC[1] | XMaxCmapsOfScreen[1] | XStringListToTextProperty[1] | XkbChangeTypesOfKey[1] | XwcDrawImageString[1] |
| XESetCreateFont[1] | XMaxRequestSize[1] | XStringToKeysym[1] | XkbComputeEffectiveMap[1] | XwcDrawString[1] |
| XESetCreateGC[1] | XMinCmapsOfScreen[1] | XSubImage[1] | XkbComputeRowBounds[1] | XwcDrawText[1] |
| XESetError[1] | XMoveResizeWindow[1] | XSubtractRegion[1] | XkbComputeSectionBounds[1] | XwcFreeStringList[1] |
| XESetErrorString[1] | XMoveWindow[1] | XSupportsLocale[1] | XkbComputeShapeBounds[1] | XwcLookupString[1] |
| XESetEventToWire[1] | XNewModifiermap[1] | XSync[1] | XkbComputeShapeTop[1] | XwcResetIC[1] |
| XESetFreeFont[1] | XNextEvent[1] | XSynchronize[1] | XkbCopyKeyType[1] | XwcTextEscapement[1] |
| XESetFreeGC[1] | XNextRequest[1] | XTextExtents[1] | XkbCopyKeyTypes[1] | XwcTextExtents[1] |
| XESetPrintErrorValues[1] | XNoOp[1] | XTextExtents16[1] | XkbFindOverlayForKey[1] | XwcTextListToTextProperty[1] |
| XESetWireToError[1] | XOMOfOC[1] | XTextPropertyToStringList[1] | XkbForceBell[1] | XwcTextPerCharExtents[1] |
| XESetWireToEvent[1] | XOffsetRegion[1] | XTextWidth[1] | XkbFreeClientMap[1] | XwcTextPropertyToTextList[1] |
| [1] | X11R6.4 Xlib - C library |