Chapter 7
Memory

This chapter describes the Plug-in API functions that allocate and free memory as needed by the plug-in.

Because plug-ins share memory space with Communicator, they can take advantage of any customized memory-allocation scheme the browser has. Browser memory schemes may be more efficient than standard OS memory functions, and can give the browser flexibility in the way it manages memory. In addition, the plug-in usually has the option of using its own memory functions.

The methods that handle memory belong to the Netscape group of methods.

• NPN_MemAlloc allocates memory from Communicator's memory space. Use this function to allocate memory dynamically.
• NPN_MemFree requests that Communicator free a specified block of memory. Use this function to free memory allocated with NPN_MemAlloc.
• NPN_MemFlush requests Communicator to free up a specified amount of memory if not enough is currently available for the plug-in's requirements.

• Allocating and Freeing Memory
• Flushing Memory (Mac OS only)

• NPN_MemAlloc allocates a specified amount of memory in Communicator's memory space.
• NPN_MemFree deallocates a block of memory allocated using NPN_MemAlloc.

• A call to NPN_MemAlloc is more likely to succeed. Communicator may be able to deallocate nonessential memory structures in response to a request.
• NPN_MemAlloc uses the Communicator's customized memory-allocation scheme, which is typically faster and causes less fragmentation than the standard OS memory functions.
• If the plug-in uses NPN_MemAlloc, Communicator is able to manage memory more efficiently because it knows how much memory the plug-in is using at any given time.

void *NPN_MemAlloc (uint32 size);

The NPN_MemFree method deallocates a block of memory that was allocated using NPN_MemAlloc only. NPN_MemFree does not free memory allocated by other means.

void NPN_MemFree (void *ptr);

[Top] [Allocating and Freeing Memory]

For example, suppose that the plug-in calls NewGWorld, and that the call fails because of insufficient memory. The plug-in should try calling NPN_MemFlush to free enough memory. If NPN_MemFlush returns a value indicating that enough memory was freed, the plug-in can call NewGWorld again. Calling NPN_MemFlush is particularly important to systems with small amounts of RAM and with virtual memory turned off.

To request that Communicator free as much memory as possible, call NPN_MemFlush repeatedly until it returns 0.

uint32 NPN_MemFlush(uint32 size);

[Top] [Flushing Memory (Mac OS only)]

Last Updated: 01/15/97 16:36:57