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https://issues.apache.org/jira/browse/GUACAMOLE-2124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18016558#comment-18016558
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Nick Couchman commented on GUACAMOLE-2124:
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[~orangeguo]: Please feel free to create a pull request for these changes!
> Replace pthread_key_t with scalable thread-local storage to overcome 1024 key
> limitation
> ----------------------------------------------------------------------------------------
>
> Key: GUACAMOLE-2124
> URL: https://issues.apache.org/jira/browse/GUACAMOLE-2124
> Project: Guacamole
> Issue Type: Improvement
> Affects Versions: 1.6.0
> Reporter: orange-guo
> Priority: Major
>
> h2. Problem Statement
> During production testing, we discovered that guacd fails when handling more
> than approximately 60 concurrent SSH connections with the error message
> indicating pthread key exhaustion (exceeding 1024 limit).
> This is a critical scalability limitation that prevents Guacamole from
> supporting high-concurrency deployments.
> *Error observed:*
> pthread_key_create failed: Resource temporarily unavailable
> h2. *Root Cause Analysis*
> The issue stems from the pthread implementation's hard limit of 1024
> thread-specific storage keys per process (PTHREAD_KEYS_MAX).
> Each connection appears to consume multiple pthread keys through:
> 1. Error handling system (src/libguac/error.c): Uses pthread_key_t for
> thread-local error state
> 2. Reentrant rwlock implementation (src/libguac/rwlock.c): Uses pthread_key_t
> to track per-thread lock ownership
> With multiple connections, the cumulative pthread key usage quickly exceeds
> the system limit.
> h2. *Proposed Solution*
> Replace pthread_key_t usage with a custom thread-local storage
> implementation that:
> 1. Eliminates the 1024 key limit by using hash-table based storage
> 2. Maintains API compatibility with existing pthread_key_t usage patterns
> 3. Improves performance by using direct __thread storage where possible
> 4. Preserves thread safety and cleanup semantics
> h2. Expected benefit:
> This change should allow guacd to handle hundreds of concurrent connections
> instead of being limited to ~60 SSH connections.
> h2. Request
> We would like to contribute this enhancement to improve Guacamole's
> scalability for high-concurrency deployments. The implementation is ready for
> review and testing.
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