ImageGear for C and C++ on Linux v20.0 - Updated
API Reference Guide > Core Component API Reference > Core Component Functions Reference > Thread Functions > IG_thread_image_lock

This function locks HIGEAR for a particular operation.


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        HIGEAR hIGear,
        AT_MODE nLockMode


Name Type Description
hIGear HIGEAR HIGEAR image handle
nLockMode AT_MODE The lock mode (IG_THREAD_LOCK_READ or IG_THREAD_LOCK_WRITE) indicator. Several threads can perform read lock concurrently, but only one thread is allowed to do write lock.

Return Value:

Returns the number of ImageGear errors that occurred during this function call.

Supported Raster Image Formats:

This function does not process image pixels.


Copy Code
hIGear = pDoc->hMainGear;
        nErrCnt = IG_thread_image_lock( pDoc->hMainGear, IG_THREAD_LOCK_WRITE ); 
        if (nErrCnt == 0)
                // locked successfully
                IG_IP_rotate_multiple_90( hIGear, IG_ROTATE_90 );
                IG_thread_image_unlock( pDoc->hMainGear, IG_THREAD_LOCK_WRITE ); 


Two APIs (IG_thread_image_lock(), IG_thread_image_unlock()) are required for those rare situations in which two or more threads-at least one of which is modifying or deleting an image-are simultaneously accessing the same HIGEAR. For example, one thread can save HIGEAR to a JPEG file (read access to a HIGEAR), while another is performing rotation in the asynchronous mode (write access to a HIGEAR). Thus, the "saving" thread would be required to call lock/unlock with the read mode as a parameter, and the "rotation" thread would be required to call lock/unlock with the write mode as a parameter.

Please note that all auxiliary HIGEARs associated with the main HIGEAR (such as Alpha channel, NRA mask, and transparency mask) need to be locked separately.

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