# US 2008/0313656 A1 · User mode stack disassociation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0313656 A1 - Document ID: US20080313656A1 - Status: Published application - Kind: A1 - Application number: 11/820,164 - Filed: 2007-06-18 - Published: 2008-12-18 - Earliest claimed: 2007-06-18 - Assignees: Microsoft Corporation - Inventors: Matthew D. Klein; Paul England - Web page: https://patentgrep.com/patent/US20080313656A1 ## CPC - G06F 9/545: {where tasks reside in different layers, e.g. user- and kernel-space} - G06F 9/544: {Buffers; Shared memory; Pipes} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract Various technologies and techniques are disclosed for allowing a user mode stack to be shared by multiple contexts. A user mode stack can be shared between execution contexts that are guaranteed to not need the user mode stack at the same time. For example, each user mode portion of a kernel thread is provided with a dedicated backing thread. When a respective dedicated backing thread is sleeping and not using a respective user mode stack, the user mode stack is allowed to float with a respective user mode portion to other kernel threads. The user mode stack is disassociated from the kernel portion of the thread. The kernel is notified of an address of a user mode thread context. The kernel mode portion of the converted thread becomes a backing thread that waits. The user mode portion of the converted thread can be switched without entering the kernel. ## Claims ### Claim 1 A computer-readable medium having computer-executable instructions for causing a computer to perform steps comprising: share a user mode stack between at least two execution contexts that are guaranteed to not need the user mode stack at a same time. ### Claim 2 (depends on 1) The computer-readable medium of claim 1, wherein one of the at least two execution contexts is a kernel thread other than an initial kernel thread that is initially associated with the user mode stack. ### Claim 3 (depends on 1) The computer-readable medium of claim 1, wherein one of the at least two execution contexts is a dedicated backing thread. ### Claim 4 (depends on 1) The computer-readable medium of claim 1, further having computer-executable instructions for causing a computer to perform steps comprising: provide a user mode portion of a kernel thread with a dedicated backing thread, with the user mode stack being assigned to the user mode portion. ### Claim 5 (depends on 4) The computer-readable medium of claim 4, wherein the user mode stack floats with the user mode portion to other kernel threads when the dedicated backing thread is sleeping. ### Claim 6 (depends on 5) The computer-readable medium of claim 5, wherein the user mode stack is correctly re-associated with the dedicated backing thread when the dedicated backing thread wakes up. ### Claim 7 A method for sharing a user mode stack between multiple contexts comprising the steps of: providing each user mode portion of a kernel thread with a dedicated backing thread; and when a respective dedicated backing thread is sleeping and not using a respective user mode stack, allowing the user mode stack to float with a respective user mode portion to other kernel threads. ### Claim 8 (depends on 7) The method of claim 7, further comprising: re-associating the respective user mode stack with the respective backing thread when the respective backing thread wakes up. ### Claim 9 (depends on 7) The method of claim 7, wherein the respective backing thread is woken up when the user mode portion needs to perform work on the respective backing thread. ### Claim 10 (depends on 9) The method of claim 9, wherein execution is resumed in a user mode procedure that restores correct values before continuing execution. ### Claim 11 (depends on 10) The method of claim 10, wherein the correct values include an instruction pointer. ### Claim 12 (depends on 10) The method of claim 10, wherein the correct values include a stack pointer. ### Claim 13 (depends on 10) The method of claim 10, wherein the correct values include non-volatile register values. ### Claim 14 (depends on 7) The method of claim 7, wherein the respective user mode stack is not dedicated to the backing thread. ### Claim 15 (depends on 7) A computer-readable medium having computer-executable instructions for causing a computer to perform the steps recited in claim 7. ### Claim 16 A method for disassociating a user mode stack from a kernel portion of a thread comprising the steps of: when a particular thread is converted to a converted thread that can be switched in user mode, notifying a kernel of an address of a user mode thread context; a kernel mode portion of the converted thread becomes a backing thread that waits using a kernel mode wait primitive; and allowing a user mode runtime to switch a user mode portion of the converted thread without entering the kernel. ### Claim 17 (depends on 16) The method of claim 16, wherein during process initialization, a context restoration procedure is registered with the kernel. ### Claim 18 (depends on 16) The method of claim 16, wherein the address remains constant for a life of the user mode portion. ### Claim 19 (depends on 16) The method of claim 16, wherein the address is stored in a kernel mode thread control structure for later retrieval. ### Claim 20 (depends on 16) A computer-readable medium having computer-executable instructions for causing a computer to perform the steps recited in claim 16.