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Each client connection is handled in its own thread (_handle_client), and that thread calls the GIMP API directly via execute_command. If a command runs longer than the MCP server's socket timeout, the server gives up, and the next tool call opens a new connection while the first command is still running. Two threads then drive the libgimp wire protocol concurrently, and GIMP shows:
Plug-in crashed: "gimp-mcp-plugin.py"
The dying plug-in may have messed up GIMP's internal state.
The 10 s socket timeout makes this easy to hit with ordinary work. Merging and exporting a 2000×2000 image with 16 layers takes about 8 s. A full render of a 16-bit image takes about 30 s, and convert_precision to 16-bit took more than 60 s.
Changes
Plugin: a threading.Lock around execute_command. Commands now run one at a time, so a retry waits for the running command instead of racing it.
Server: the socket timeout goes from 10 s to 300 s, so long operations return their result instead of failing.
Testing
Tested manually on Windows 11 with GIMP 3.2.6:
Before: an exec call that timed out, followed by another call, crashed the plugin. This happened twice.
After: a long session with repeated 20–30 s renders and filter edits on a 16-bit 2000×2000 image ran without a crash.
Each client connection is handled in its own thread, which calls the
GIMP API directly. When a long-running command exceeds the client-side
socket timeout, the MCP server reconnects and sends the next request
while the first one is still running. Two threads then drive the libgimp
wire protocol concurrently and GIMP reports "Plug-in crashed:
gimp-mcp-plugin.py".
Guard execute_command with a lock so commands run one at a time.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Merging and exporting a 2000x2000 multi-layer image takes ~8 s, a
16-bit render ~30 s and a precision conversion over 60 s, so
get_state_snapshot, get_image_bitmap and longer exec calls ran into the
10 s timeout.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The plugin now serializes command execution across client-handler threads. The server connection socket timeout changes from 10 seconds to 300 seconds.
Changes
Command execution serialization
Layer / File(s)
Summary
Lock command execution gimp-mcp-plugin.py
The plugin initializes a shared lock and acquires it before each execute_command call. This serializes command execution across client handlers.
Socket timeout
Layer / File(s)
Summary
Set connection timeout gimp_mcp_server.py
GimpConnection.connect sets the socket timeout to 300 seconds instead of 10 seconds. The connection and error-handling flow is unchanged.
Issue 81 asks for a lock around execute_command to prevent commands from separate client connections from running in parallel. This PR adds that lock, but the issue describes wrong-image interleaving, while this PR targets a timeout followed by a new request.
Possibly related PRs
gimp-mcp/gimp-mcp#63: Both PRs change the socket timeout and command concurrency behavior. PR 63 uses a configurable timeout and GLib main-thread execution; this PR sets a 300-second timeout and uses a threading.Lock.
Suggested labels: bug
Suggested reviewers: vicarc
Merge Risk: Moderate · up to d723f
Serializing commands should stop the reported crash, but a single hung or very long command now blocks every later request until GIMP is restarted. Stalled connections can also leave MCP calls waiting up to five minutes. Bound the wait and the lock-held time before merging, or explicitly accept this behavior.
Security architecture risk: Moderate · up to d723f
Serializing commands addresses the concurrency crash, but one nonterminating command can now block every later plugin command. A client timeout does not cancel execution or release that blockage. The default endpoint remains local, and callers already had Python-execution authority, which limits the incremental security exposure.
Retained concerns
Medium · security · observed: The new plugin-wide lock remains owned for the full duration of client-controlled execution. A nonterminating command blocks all later commands, including in-band status and restart requests; client timeout or socket restart does not restore command processing. This is a new failure-containment behavior, although the same callers already possessed unrestricted Python-execution authority.
Security review details
Security Blast Radius
inferred — The newly shared availability dependency covers every command handled by one MCPPlugin instance, including commands concerning different images and in-band health or restart requests. Exploitation requires command access to that instance. Default localhost binding limits direct network reachability; broader deployment or cross-tenant exposure is not established.
Security Findings and Attack Paths
observed — The retained denial-of-service finding follows a concrete path: a connected caller submits Python code, the handler acquires the shared lock, and nonterminating execution retains it indefinitely while later handlers wait. A client timeout only closes the client socket. This introduces a lock-based blocking mechanism, not a new maximum process-disruption capability, because unrestricted code execution already existed.
Trust Boundaries and Controls
observed — The new lock enforces mutual exclusion, not caller authentication, code isolation, or an execution budget. Normal completion and exception unwinding release it, and ordinary command exceptions become error responses. These controls contain concurrent protocol use but do not terminate a command that never returns.
Resilience and Maintainability Implications
inferred — In-band recovery shares the blocked execution path, while listener-only recovery does not reclaim active command ownership. Safely restoring availability after nontermination therefore requires more than reconnecting or rebinding the socket; releasing the lock while the original command continues would undermine the serialization guarantee.
Hardening Proposals
proposed — Define bounded admission and explicit request-lifecycle states so abandoned queued work can be rejected before execution. For nonterminating active work, provide an out-of-band recovery procedure that stops the owning execution context before accepting new commands; do not treat socket timeout or forced lock release as safe cancellation.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
Status
Explanation
Resolution
Docstring Coverage
Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
Check name
Status
Explanation
Description Check
Check skipped - CodeRabbit’s high-level summary is enabled.
Title check
The title clearly describes the main change: preventing a plugin crash after a client-side timeout. It is concise and related to both the command serialization and increased socket timeout.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Full details: Docstring Coverage
Explanation
Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 2 functions across 2 files.
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
Finishing Touches
Generate unit tests (beta)
Create a new PR
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Actionable comments posted: 2
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @gimp_mcp_server.py:
- Line 32: Separate connection and command-read timeouts in the socket setup:
set a 10-second timeout before `connect()` and switch to 300 seconds after the
connection succeeds, before command reads begin. Preserve the existing
`send_command()` behavior; do not add a total-wait deadline unless the
implementation or review scope requires one.
Review comments at @gimp-mcp-plugin.py:
- Line 61: Update the command execution path in _handle_client so
client-supplied j["cmds"] cannot hold self.command_lock indefinitely: use an
execution model that can actually cancel a running command, or reject commands
that cannot be bounded. A lock-acquisition timeout alone does not bound the
command already holding the lock.
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Reviewing files that changed from the base of the PR and between 7325865 and d723f40.
Files selected for processing: 2
gimp-mcp-plugin.py
gimp_mcp_server.py
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Problem
Each client connection is handled in its own thread (
_handle_client), and that thread calls the GIMP API directly viaexecute_command. If a command runs longer than the MCP server's socket timeout, the server gives up, and the next tool call opens a new connection while the first command is still running. Two threads then drive the libgimp wire protocol concurrently, and GIMP shows:The 10 s socket timeout makes this easy to hit with ordinary work. Merging and exporting a 2000×2000 image with 16 layers takes about 8 s. A full render of a 16-bit image takes about 30 s, and
convert_precisionto 16-bit took more than 60 s.Changes
threading.Lockaroundexecute_command. Commands now run one at a time, so a retry waits for the running command instead of racing it.Testing
Tested manually on Windows 11 with GIMP 3.2.6:
execcall that timed out, followed by another call, crashed the plugin. This happened twice.🤖 Generated with Claude Code
Summary by CodeRabbit