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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 the browser, 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 browser group of methods.
- allocates memory from the browser's memory space. Use this function to allocate memory dynamically.
- requests that the browser free a specified block of memory. Use this function to free memory allocated with
- requests the browser to free up a specified amount of memory if not enough is currently available for the plug-in's requirements.
Allocating and freeing memory
To allocate memory and free memory, use these paired functions:
NPN_MemAllocallocates a specified amount of memory in the browser's memory space.
NPN_MemFreedeallocates a block of memory allocated using
The plug-in can call the Plug-in API
NPN_MemAlloc function instead of the standard malloc function to allocate dynamic memory. Using
NPN_MemAlloc offers several advantages to the plug-in.
- A call to
NPN_MemAllocis more likely to succeed. The browser may be able to deallocate nonessential memory structures in response to a request.
NPN_MemAllocuses the browser'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, the browser is able to manage memory more efficiently because it knows how much memory the plug-in is using at any given time.
The Mac OS browser frequently fills its memory partition with cached data that is purged only as necessary. Since
NPN_MemAlloc automatically frees cached information if necessary to fulfill a request for memory, calls to
NPN_MemAlloc may succeed where direct calls to
NPN_MemAlloc method has the following syntax:
void *NPN_MemAlloc (uint32 size);
size parameter is an unsigned long integer that represents the amount of memory, in bytes, to allocate in the browser's memory space. This function returns a pointer to the allocated memory or null if not enough memory is available.
NPN_MemFree method deallocates a block of memory that was allocated using
NPN_MemFree does not free memory allocated by other means.
void NPN_MemFree (void *ptr);
ptr parameter represents a block of memory previously allocated using
Flushing memory (Mac OS only)
NPN_MemFlush method frees a specified amount of memory. Normally, plug-ins should use
NPN_MemAlloc, which automatically frees nonessential memory if necessary to fulfill the request. For Communicator 4.0 and later versions, this function is not necessary for the Mac OS platform;
NPN_MemAlloc now performs memory flushing internally. You need to use
NPN_MemFlush only when it is not possible to call
NPN_MemAlloc, for example, when calling system methods that allocate memory indirectly. If
NPN_MemAlloc is called, calls to
NPN_MemFlush have no effect.
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 the browser free as much memory as possible, call
NPN_MemFlush repeatedly until it returns 0.
uint32 NPN_MemFlush (uint32 size);
The size parameter is an unsigned long integer that represents the amount of memory, in bytes, to free in the browser's memory space. This function returns the amount of freed memory, in bytes, or 0 if no memory could be freed.